Most of this article feels like it's discussing irrelevant methods, you only need GPS to get it close (well for what they're doing they don't need GPS at all, though I'm sure it's used), we have much much more accurate ways of measuring the positions of things from a fixed reference point, 0.5cm deviation on your positional measurement is trivially achievable with optical systems. Why is the author spending paragraphs discussing IMU accuracy when we're trying to line up a rocket with a tower. You care about the rocket's relative position to the tower, you can put your measurement equipment on the tower, you don't need to worry about how accurate your accelerometers are.
I assume they are doing something much more clever/hardened, but you can trivially achieve much greater spatial accuracy with a Vive Tracking Puck for like $100.
Certainly lab equipment can measure distances well below 1 um fairly easily, I could manage 1 um in my garage. The issue is that the conditions at time of catch are VERY dynamic and not at all lab-like.
Your positioning system needs to acquire a fix at least 100m out in variable atmospheric conditions on a rocket undergoing heavy acceleration and dumping all kinds of heat, smoke and vibrations into itself, the atmosphere, and everything around it.
In addition having a fix on your tracking device is only half the game, not you have to figure out where the rest of the rocket is in relation to your tracking device. Which again, vibrations, temperature and manufacturing all have an effect.
So while yet, a vive tracking puck isn't entirely unlike the workable solution it is also entirely unsuitable as a solution and should not be used as a baseline to measure off of.
So? Yeah it's a challenging environment, we know that. My point is that the default way to solve this problem is to track your object from your reference point.
Bill Gerstenmaier was talking about the flight test 4 landing accuracy, which landed on the open sea in the Gulf of Mexico, not on the tower like the recent test flight 5. The only thing nearby was a buoy. I'm pretty certain it didn't have advanced laser systems.
There’s a big cross in the middle of the landing pad that you’re trying to aim for - you don’t need advanced laser systems to get an accurate fix on where the landing pad is from the rocket - or where the rocket is form the landing pad for that matter.
> Bill likely misspoke or was talking about control error.
Mixing up control errors with absolute errors is a very common form of miscommunication in robotics.
I work with relatively big robots and often my colleagues would say something like this "During the test we had 0.5m cross track error, so we did X, Y, Z ...".
And I always ask them for clarification. Were they looking at the robot and seeing that it is half a meter off where it should be, or were they looking at a screen and seeing that the robot thinks it is half a meter off from where it wants to be? Because those are two very different situations. And both can be described with the same words. (And sometimes it can be both, or just one of them.)
Control error is defined as the difference between desired value and measured value. So this is pretty good?
Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.
Not sure what you are talking about. If you are asking if 0.5cm is good controller error for an orbital class launcher on landing? Yes, it is extremely good. Without doubt.
If you are asking about my tangential story where there is confusion between total error vs controller error then no, it is not good. Confusion is never good. Especially if the system is not within the total error budget. Because to improve it you need to know if you are dealing with measurement error or controller error.
> Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.
Sure. I doubt that their total error is within 0.5cm, but both of their landings were extremely succesfull.
The robot knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation.
This voice sounds like something that Mark Farina should be dubbing into his next album. But it's the first time I've heard this bit. Where did it come from? Is this a classic in engineering circles of some shit Rockwell actually sold to the military?
It's from an old air force training video. Best guess I'be heard it that it's an unsuccessful attempt to explain Kalman filters (or something similar) in layman's terms.
It's definitely floated around for a while, but it grew in popularity in the past few years.
The article discusses the absolute error coming from RTK systems and claims that it won't be as low as 0.5cm, but surely the relevant metric is relative error, and I can see commercial systems advertising that level of precision.
i.e. the booster doesn't know it's actual position to within 0.5cm but it knows it's position relative to a buoy or the catch arms to that precision.
Rtk already is 'relative' error- it requires one or more base stations (with either known absolute location or assumed one for relative positioning).
But survey grade gnss is a web of rabbit holes, if you want to get into it.
And there are ways to get sub mm accuracy both relative and absolute, but idk of one that would be quick enough for the required reaction time of dynamic landing via 'catching'.
But multi-centimeter (4-5) that's really easily doable is probably good enough for other systems to take over from.
When Tim of EverydayAstronaut quoted this[1], as I recall the quote was within 0.5cm of the target landing site. So I assumed that to be relative accuracy and not absolute.
My lawnmower (openmower) can do <2cm accuracy over GNSS. It is absolutely believable they could achieve 0.5cm on GNSS (plus rtk correction data from a fixed base station nearby) alone without measuring any relative distance using other systems.
Well, it isn't "uncorrected". It's just that you don't need any additional hardware other than a second gnss receiver on the base station and some kind of link between them.
GNSS is more than accurate enough once you know all slight errors in satellite orbits and the atmospheric distortions currently affecting the area near the base station and can correct for them.
It's significantly more difficult to actually land a jumbo jet sized rocket booster with that precision than to measure its own relative position. Gerstenmaier was talking about landing accuracy. My guess is that measurement accuracy is a red herring. More likely it was a slip of the tongue (the good man is 70 years old) and he meant to say it landed with a 0.5 meter, not centimeter, accuracy relative to the buoy.
I'd be very interested in the systems advertising that! I have not seen that even for stationary surveying equipment. I think it's also important to distinguish between RMS error which is often the better topline spec that companies give you, vs the 95% confidence error which is the more relevant one for flight reliability.
In the specific case of a docking-type manoeuvre presumably you only need the highest accuracy when you're getting very close to the target.
No reason you couldn't use RTK GPS for <10cm accuracy for most of the flight, then in the last few meters of landing switch over to to high-precision, short-range tracking - like optically tracking a marker on the grabbing arm.
For other specific cases - like bridge monitoring - there are reports of 2–3 mm precision [1]. Of course, bridge monitoring has quite distinctive requirements; a 5Hz vibration component and a 0.0001 Hz thermal expansion component. So there's a lot of potential to average over lots of readings to reduce noise.
Global lat/long coordinates are defined in terms of coordinate systems like WGS84 or ITRF2020, which are themselves the result of relative measurements between reference stations.
The earth's crust floats on top of liquid rock. This matters at relevant length and time scales; in most places, these effects alone are on the order of millimeters per year. One reason why it's better to use NAD83 over WGS84 in North America is that NAD83 latitudes and longitudes move with the North American plate.
Positions _are_ relative, and the closer you can put your datum, the less drift you'll accumulate.
There is a literal, autistic sense in which you are correct. But there is a practical, pragmatic distinction between measurements that we call absolute versus those we call relative, and pedantic correctness misses the point.
I found this video from the perspective of a landing pin interesting, especially when played back at low speed: https://youtu.be/ExV6PHRM8eI?t=17
You can see the arm comes in, then there's some side-to-side bounce (not sure how much is the rocket bouncing off vs. the arm fine-tuning its position). Just after contact seems to be made, and before the shock absorbing (or yaw-correcting) pistons drop much, there's a large flash from the engine. Is that a characteristic of engine shutoff, or was there a last-second "hover" push just before shutoff and drop? I wonder how much force the arms felt.
Another perspective showing both arms, and (as mentioned in the article) how the left one adjusted more significantly at first: https://youtu.be/JlcrNakUGVs?t=3
Well, to be fair, the engineers working on this system have been thinking about the accuracy this whole time even if you haven't. Even on the first go, it still had to land on a relatively small pad floating in the ocean.
As impressive as the space efforts in the 60s and 70s were, I've often thought that they were a false start created by a war-like impetus to show off. Tech-wise, we really weren't ready for a space age. The sort of control systems that make this sort of outcome possible haven't been around for all that long, really, especially if you mark them from being economical and not just "it technically existed in a lab somewhere". Plus if you really dig into how these rockets are built and maintained, you see a lot of other technologies that have not been around for that many decades, like, practical and reliable 3D printing, and computing simulations that have more computational power per second than the entire computing world could scrape together in a year in the 1960s, and those are just the highlights, not the exhaustive list.
A lot of people are like "we got to the moon in the 1960s, where's the progress we should have had since then?" but I see the 1960s as the bizarre exception rather than the thing that should be used to set the rule. There was no way the space age was going to happen then, in an era where you're almost sitting there counting each bit of RAM you can afford to send into space. The true Space Age is just dawning now, and it's still early in the dawn; we still have to have massive international cooperation to put a single space station up, we can't do something as basic as refuel in orbit, we just barely started having people in space for commercial rather than governmental reasons... it's just the beginning.
I think it's not so much that we weren't ready for a space age tech-wise, but that the the reason we have so much of our technology today is because of investments made in the 1960s. NASA had basically unlimited money to throw at every technical challenge in the way of landing a human on the moon.
The apollo program drove the need for more computational power, more memory, better guidance and navigation and control systems, better materials, experiments to better understand many phenomena, etc. And after the apollo program ended, the contractors that developed those technologies on NASA contracts could just commercialize them. And the data from experiments, on materials, aerodynamics, combustion, and so on, that is publicly available has made engineering so much cheaper and easier.
I think the 60’s showed how much humans can achieve in terms of innovating with very little (in terms of tech). Now, we’re seeing how much can be achieved with a whole lot more. And, I agree, the space age really does feel like it’s only just heating up. Very exciting time!
> There was no way the space age was going to happen then, in an era where you're almost sitting there counting each bit of RAM you can afford to send into space.
And yet, they got to space. Better computers are not the solution to every problem. And it wasn't a false start. We are already in a space age, we have been for quite a while. It didn't stop at Apollo. We have satellites for the military, TV, weather, various forms of communication, navigation (GPS...), telescopes, space stations, probes and rovers. We do science, commercial and government operations. Starlink is great, but it is just the continuity of all the space communication abilities we developed over the years.
I think computers are not what will enable the "true space age". Sure, they help, and SpaceX, if successful with their Starship will certainly be a big advance, but I think that we are missing a key ingredient to reach the "true space age" and it is nuclear power. Starship maybe could get us a settlement on Mars with hundreds if not thousands of launches and refueling missions. Project Orion was to launch an entire colony in one go, return trip included. Even Saturn was considered feasible. Project Orion is mad, but it goes to show how limiting chemical rockets are compared to nuclear.
And it is something we probably could have done already, without modern computers and 3D printing, if we wanted to. It is maybe a good thing that we didn't though. Spreading radioactive material in the atmosphere and mass producing thermonuclear bombs is kind of scary.
Armchair aerospaceing here, but it feels like he's a whole class of positioning sensors in this analysis. It seems to be you only need GPS and related absolute positioning systems to get you close to the tower. At that point, what you care about is the relative positioning of the tower and the booster. I would think this can be done very accurately with a host of options: cameras, radar, lasers, ILS style systems, etc, etc.
Right? They land fighter jets on carriers with a light signal that projects out from the ship at a particular angle. It seems very easy to do something like this with some form of electromagnetic radiation. Or have some way for the tower to detect the exact position and communicate with the rocket.
I understand engineering is complicated but this honestly seems like the easiest part of the problem to solve.
It's more likely that SpaceX determined they didn't need super tight tolerances and called it a day.
Carrier landings are accomplished using a combination of indications, and the meatball is only one of three primary tools. If you are not flying an on-speed angle of attack AND lined up on the centerline of the landing area, the meatball position is invalid to a degree proportional to the degree to which those other inputs are off.
The meatball Fresnel lens is canted slightly side-to-side, and only places the hook in the right spot at a given angle of attack. Which is a design compromise necessitated by having to allow multiple types of aircraft with multiple hook-to-eye distances to land on the same aircraft carrier while using a visual input in one location (the cockpit) to properly place a device in another location (the hook point) with high precision.
Source: I've done it.
So just as it is not "very easy" to trap on board the boat with "just" a light signal, I would assume landing a building-sized booster has a similar if not bigger list of potential "gotchas."
> SpaceX determined they didn't need super tight tolerances and called it a day
Yup! This is my conclusion in the article - the landing box for the Super Heavy booster is 5x13x18 meters on each side, with 5-15 degrees of angular tolerance in each of the vehicle axes. So the margins are big enough that you don't need millimeter level precision for the rocket position.
My take is that it would probably be possible with enough effort, but there isn't an easy solution. And if you don't need it then the best part is no part. :)
GNSS RTK is incredibly accurate these days. By the time that you're close enough to the landing zone, you're close enough to get positioning down to centimeters on consumer grade hardware, which the article points out.
The actual question is literal: Can SpaceX land a rocket with sub 1 cm (1/2 cm) accuracy? GNSS RTK can get you down to a couple of centimeters, but getting more granular resolution than this isn't reliably possible with current professional grade technologies.
I'm personally unsure if the military has greater resolution than what's possible with RTK or w.r.t. military use GPS, but I would not be surprised if they did. If that's the case, NASA would most likely have access to it, I would assume. But the article specifically calls this out saying that it's not accurate enough to surpass the resolution of using RTK.
What's really cool about these questions is that the same problem space is applicable to self-driving cars and SLAM, if you're into that sort of thing. Lane detection, etc.
Yes, for the purposes of landing speeds. In fact, at vertical aircraft landing speeds, your time-step to position Δ is more accurate than automotive SLAM.
Depends on what you define as 'traditional': basically if you want positioning information via GNSS, the techniques for getting a better reading a fairly well understood, and it doesn't really matter how good your satellites are, the atmospheric distortion is the issue and you need to model and compensate for it by measuring it with a near-enough base station, using multiple frequencies and constellations, and if you're moving, an IMU to constrain your motion over as long a period as you can to effectively average out the other noise sources. Half a centimeter, given all of the above, is better than what I've seen quoted in the space, but not utterly crazily so.
Not really, the Gyros described in the post are also essential. If you don’t know the attitude of the vehicle, you can’t point the engines in the direction your control algorithm says you should to hit the target.
Edit: I think I misunderstood the comment. Yes, you can use the absolute methods for rough guidance and then use relative positioning for the final approach. The article has a line about why the author doesn’t think that’s likely though.
0.5cm isn't even well defined, considering that the rocket itself is probably out of round by larger tolerances, not to mention issues of thermal expansion.
I would suspect it's some average of many points that the control systems try to track, because the rocket is not a point, and the press wants to quote a single easy number.
I'd expect that the rocket has a ton of sensors, and a ton of passive and semi-active tracking devices all over the body.
E.g. I'd put a bunch of NFC-type responders in a number of key positions, responding at different frequencies. Then a typical sweeping-frequency radar pulse would activate them all, and the response time and the Doppler shift would tell about positions and speeds of many points on the rocket. I'd do a similar thing with reflectors and IR/optical tracking.
All these points should follow some reasonable trajectory for some point the top of the rocket, near the chopsticks, would move towards some desired catch location point. Probably this motion is where "with precision of whatever cm" relates to.
is "surface amplitude" vibration? I could see vibration being graphed over time as a wave with an amplitude and frequency. I can't really comprehend the size of super heavy combined with the energy density of just one turbo pump on one raptor engine (let alone 33x2) and then the precision of control needed to catch the whole thing with chopsticks. Not many things do i admit are just beyond me period but this is for sure.
/raptor 3 pumps look like you could hold them in your hands but iirc they deliver over 100k horsepower each.
It's probably defined by the catch points as that's what matters: whether the catch points end up where they belong (good) or not (disaster). The catch points are not "out of round".
I should have mentioned that the catch points are on one long bar that goes atop the booster. They are not simply attached to the sides of the booster. Booster shell flexing does not affect the catch points at all.
Landing on the grid fins would be a really bad idea. Even though they're car-sized, they're not load bearing and "only" made of steel (not titanium etc. .. just yet). Starship's Raptors blast during hot staging is enough to bend them on the top. https://www.reddit.com/r/SpaceXLounge/comments/1g3bi7s/grid_...
I actually think there is some old Starbase tour interview where a SpaceX guy implied it was Musk's idea, though I could be misremembering. Catching the booster kind of makes sense, since they needed the tower arms anyway for stacking and unstacking.
Interesting, are there more than 4? because I was also amazed that the rocket was rotated at exactly the right angle to be caught by them. But maybe that is the 'easier' challenge when you are hovering with such accuracy.
I keep finding myself watching the catch every few days, and it does not tire to impress.
If you don't know how precise GPS receivers can get with dead reckoning techniques, this demo of someone "drawing" onto a map of their driveway using a GPS receiver is very impressive: https://youtu.be/3tQjIHFcJVg?t=245
It looks like they're getting measurements that are only a few inches away of the module's real position, although of course the conditions seem favorable with an unobstructed sky and consistent alignment.
The module they use is a ZED-F9P by u-blox. I've used ~$50 u-blox GPS modules in DIY electronic projects before since they're often the brand you'll get when buying GPS modules, but this particular type with dead reckoning is much more expensive. Sparkfun has it for $275 for example: https://www.sparkfun.com/products/16481.
I believe this is demonstrating the performance improvement of RTK [0] alone, not dead reckoning. GPS + dead reckoning is what phones and wearable do afaik, whereas RTK requires getting correction data associated to base stations nearby and seems mostly relevant for industrial applications (you need a subscription in the case of u-blox).
You can do even better with radar. If you place a set of radar reflectors around the tower at known locations, then you can detect them from the booster and triangulate the distances to a precise position. Plus, radar gives you relative velocities, so your speed and roll rate estimatimates get even more precise. I bet you could get down to millimeters with a setup like this.
Falcon-9 uses radar altimeters for determining vertical "distance to go" during landing.
While a sideways position error of even ten meters is not fatal, it is critical for the rocket to be quite close to zero altitude when deceleration brings the velocity to zero. (Any residual error must be dealt with by the shock absorbers, and their capability is modest.)
As the article explains, with a well designed procedure, the required navigation accuracy is quite modest. Even the latest consumer IMUs and GPS would do, and SpaceX is using even slightly more accurate "tactical grade" units, typical for all launch vehicles.
Good article. It is nice how it goes through all the points systematically.
It talks about how real time control system algorithms work with algorithms like like PID and MPC. I assume the SpaceX solution is likely one of the most advanced control systems in the world.
It is great that the author of the video helps to introduce the topic to the general audience. This is a vast and a fascinating subject with lots of material available for a further more systematic study.
It becomes more technical, if one is specifically interested in the methods used by SpaceX. But there are some overviews that describe the general idea. Here is one presentation by Behçet Açıkmese: https://nescacademy.nasa.gov/video/eda2b96bddf945629be2c9d2e...
Note that before joining SpaceX to lead their autonomous landing software development, Lars Blackmore worked at JPL, where together with Behçet Açıkmese they developed the autonomous precision landing algorithms based on real time optimization methods. So, even though SpaceX has undoubtedly developed additional nuances to match their needs and capabilities, they were building on this prior work at JPL.
It's interesting that NASA, despite working on control algorithms, apparently didn't consider using them for building a reusable rocket. (SLS isn't planned to do a propulsive landing, and neither was its predecessor Ares V.) Though they probably did use them to some extent for the "sky crane": https://en.wikipedia.org/wiki/Sky_crane_(landing_system)
Making any kind of a rocket that works is already nontrivial (once one goes beyond Estes models), but in terms of complexity of the challenge, making some kind of a hopper that goes up and down is a task that ambitious amateur groups with a few members and under $1M in funding were demonstrating even before SpaceX was founded. There is no need for a highly efficient engine, there is no need for lightweight structures. Many other concerns, such as low frequency structure oscillations, aerodynamics, etc are practically nonexistent.
Making a space launch vehicle is a task for a group with at least x100 more resources and experience. Reaching orbital velocity is pretty hard. Most startups do not succeed.
Making a space launch vehicle which does not spend the fuel entirely, while carrying extra hardware to also land after the launch is another step up in how hard this is. Very serious institutions worked on this problem since 1970s but lots and lots of people were skeptical. Shuttle was impressive, but also very expensive. Then SpaceX has shown that it was not only possible, but even practical to make ordinary rockets reusable. That was amazing. Even now, almost a decade later, nobody has shown anything like that -- though a number of Chinese startups are working on it.
> Half a centimeter landing accuracy is not possible, and Bill likely misspoke or was talking about control error.
Maybe the 1/2 cm accuracy refers to the final position of the booster's catch points on the arms after they've closed, after the booster's engines are off, and after the booster settled, and maybe they mean lateral accuracy. I would forgive them for that because that's the accuracy that actually matters here.
If the catch points were off then that might spell disaster, so the catch points' landing accuracy including the help of the catch arms is what matters.
The catch/lifting points may look small, but actually protrude from the side of the booster by 2-3 feet. Note that the booster is actually in a hover at the point the arms close in to touch it, so as long as it's vertical rotational axis is right (there are only 2 pins - one on either side), the positioning of the pins on the catching arms is basically guaranteed.
Right, so if SpaceX meant that they had an error of only .5cm maybe they meant that the error on the booster rotation angle was small enough to produce only a .5cm error at the catch points. Since they weren't specific, it's hard to know what they meant.
The booster rotation angle error and the catch point placement error were much too small to detect with the naked eye on the published videos. Every other measure of accuracy was clearly within tolerances -- and also hard to discern with the naked eye.
As amazing as .5cm accuracy sounds, if SpaceX meant catch point placement error, then it's quite as impressive because that only implies everything was within tolerance _and_ only the booster rotation angle error need have been impressively near-zero measure. That's... still amazing, honestly. If you can get the booster rotation angle error near zero then you can get the other errors way down too.
You can see the landing arms adjusting in the video as well.
His choice of stainless steel is panning out well here - I doubt if aluminum or composite body structure would hold up as well to the "grab" forces from even minor misalignment. A composite structure would likely be entirely compromised by a big scrape.
It would be interesting to see a test where the landing speeds were deliberately too high - how much deceleration can the arms handle safely?
I think the chopstick mechanism is probably the best possible catch mechanism for such a tall object. The booster will be suspended from the top, which means the booster isn't subject to tipover as it would be if landing legs were involved. We've already seen this many times in the Falcon 9 booster series.
I can't see chopsticks ever working from a droneship, though - too much induced rotation for chopsticks to compensate.
As an alternative to chopsticks, a catch 'sleeve' might be possible, though it would magnify alignment errors considerably.
I would have thought the vibration from the engines would produce error of greater that 1/2 cm. Still, it seamed to have worked well. So, there you go.
Yes, that seems like a very big hand-wavy assumption. This paragraph is quite...something:
> Could you use other real-time distance measurements like laser rangefinding or visual processing? I don’t think so – the surface of the vehicle is too irregular to get a reliable fix point, especially while it is moving, and these are vulnerable to smoke/fog/gas/ambient lighting. Technologies like Ultra Wideband are vulnerable to multipath reflections and attenuation by the booster’s steel walls, and aren’t more accurate than RTK anyway.
That is not exactly an exhaustive list of methods to locate an object.
I have no idea whether 0.5 cm precision is feasible or even needed, but this part felt a bit off.
I vaguely remember Musk talking about reflective paint for some band on the landing pad of Falcon, a long time ago.
> At the most precise, an RTK positioning system could lower position accuracy all the way down to 2.5 cm (+1cm per km of distance). If SpaceX put a receiver on the launch tower or the ocean buoys, then the landing position could be incredibly accurate. But even the most advance positioning tech won’t guarantee it down to 0.5 cm. And RTK does rely on being able to acquire and maintain a link between the booster and ground for this precision.
I don't understand this last sentence. Afaik RTK correction only requires receiving correction frames on the booster's side, which can be distributed via l-band just like GPS. I suspect the latency constraints are also quite low as the conditions aren't going to change quickly near the tower with the kind of good weather they choose for launch.
If it's positioning relative to the chopsticks, I'm sure it's possible to know where you are within a centimeter, even with all the rocket exhaust flying around. That's what DGPS is all about.
It's still wildly un-nerving to me that there's no publicly stated option other than the chopsticks for landing(edit: some future passenger craft). Imagine if you've got enough fuel to avoid slamming into the ground, and a nice big ocean, or a lake sufficiently deep... couldn't a water landing happen and let future passengers survive?
This is not the passenger vehicle. That's the second stage, this is the first stage booster. They've also landed the second stage but that did a water landing from orbit which in many ways is even more impressive.
I think they were simply speaking of the final pads the rocket rests on top of the chopsticks have 5cm of error either direction.
But judging from the bouncing the rocket did when in the chopsticks the error for positioning into the initial catch position is much larger in all directions. The chopsticks coming closed around the rocket do the heavy lifting for final alignment to that 5cm I imagine.
From what I understand this is the primary difference and problem with Falcon 9 vs. Super Heavy.
From the Article:
"Why can't SpaceX do a catch with a Falcon 9?
-It does not have separate landing propellant tanks, so propellant slosh will disturb its trajectory. The Super Heavy booster has dedicated central header tanks for landing propellant, so there should be minimal propellant slosh to disturb the vehicle attitude.
-It lands with a single engine which cannot throttle low enough to hover the vehicle, and as such must perform a “hoverslam” maneuver to bring the vehicle to a stop right on the ground. While the Super Heavy booster must perform most of a hoverslam maneuver to slow down just before coming in to the tower, it can hover for the final fine positioning.
-Because it lands with a single engine, roll control is minimal close to touchdown when the airspeed is low and the grid fins can impart minimal torque, and is limited to its weaker cold-gas thrusters. The Super Heavy booster can control roll with its 3 engines all the way to the ground.
-Falcon 9 has no engine-out capability for landing. SpaceX has not confirmed it for the Super Heavy booster, but I believe one engine out is likely possible (more on this later).
-It is smaller with a lower moment of inertia. Rockets get more stable and easier to control the larger they are, much like it’s easier to balance a broom on your finger than a pencil.
-It is smaller, and so thanks to the cubed-square law has a higher area:mass ratio. This means that it will be more affected by wind gusts that might blow it off course."
The accuracy that counts is for the gap between the arms and the booster, which could well be 1cm since they can measure that with sensors as the booster descends between the arms, and the arms can be controlled accurately.
If they did that and hit them consistently.. talk about rubbing salt in the wounds of the rest of the industry. It would be like a sports team running up the scoreboard on an obviously beaten opponent. Super heavy hitting X's painted on the chopsticks right in the middle would be border line unsportsman-like heh.
It’s a really good idea! Unfortunately not too much, since the error is largely from atmospheric distortion of the signal and so the error for two receivers close by would be correlated. You’d need the error to be uncorrelated to gain accuracy with multiple receivers.
NASA own estimation is that is only funding about 50%. They mentioned that SpaceX is matching their contribution.
But of course this ignores that before the contract, SpaceX had already been working on this for many years. Raptor development began in 2014ish.
I would estimate SpaceX pays more then 50%. By reports they are currently investing like 1.5 billion $ a year. And the government contract can't finance half of that.
Also, of course in all of NASA history, this is the first time that anybody ever expected to invest themselves. The idea that a company would spend so much to build a moon lander for NASA is not something that was even an option a few years ago.
So why should tax payers be angry even if NASA paid 100%. Unless of course people are just angry that the space program exists at all.
Take a look at videos on YouTube by ThunderF00t. SpaceX is pretty problematic. Currently, around 80% of SpaceX's rockets are dedicated to launching Starlink satellites. This is because they've already soaked up all the demand for satellite launches, and things like starship don't really have a reason for existing. Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
My view is that Tesla, SpaceX, etc. are just cults of personality. Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
Thunderf00t has basically 0 credibility when it comes to SpaceX. He predicted that starlink couldn't ever work, for example. In fact, he even thought that this landing would fail.
Like he might have good point hidden somewhere, the issue is that we know that he will reflexively "debunk" anything SpaceX does, and predict failure every time. Meaning that his takes on SpaceX are beyond useless.
Edit: Just out of curiosity, I looked up his video about Starlink, and his point was it's a bad business, not that it's physically impossible to do it:
I'd actually love it if you could find a single thing he says in that video that's provably false. I'm quite confident history will judge Elon Musk properly, as the "Too Big To Fail" version of Theranos and Elizabeth Holmes.
Talking about someone's track record of predictions is not an ad hominem, in the context of evaluating their credibility with respect to the subject of those predictions.
An ad hominem attack occurs when someone attacks the person making the argument rather than addressing the argument itself. For example, saying "You're always wrong, so you're wrong about this too" without addressing the current claim would be ad hominem.
That's exactly what the person I responded to was doing.
> Take a look at videos on YouTube by ThunderF00t. SpaceX is pretty problematic.
Response:
> Thunderf00t has basically 0 credibility when it comes to SpaceX. He predicted that starlink couldn't ever work, for example. In fact, he even thought that this landing would fail.
You’re claiming Thunderf00t is a good resource on SpaceX. The response gave examples of how he’s been consistently wrong.
>They claim they're going to get these laser communications between the satellites which will make things faster for a long distance... [this is because light travels faster in a vacuum than through fiber optic cable you up to London a very important one for the Global Financial system Starlink latency is under 50 milliseconds while the current Internet is around 70 milliseconds] yeah Starlink can't do any of that at the moment.
>Probably something to do with the fact that the satellites are hundreds of miles or kilometers apart and you're trying to hit a tiny moving Target from another moving target with a laser and then and chaining those together that doesn't sound very easy but they're promising to launch some satellites that can do it in the next generation [getting close to launching satellite 1.5 which has laser interest satellite links]
>Now where have I heard that before... Let's just call me skeptical on this one
This entire video is just the same thing over and over. As is usual with him, he doesn't actually make any strong enough claim and just goes on endless sneering. But in the context of the video, it is absolutely clear that he's saying it is just another lie and that it's basically impossible. Remember, this was mere months before the laser network went up. He also claimed that the bandwidth is never going to be usable, but it absolutely is.
Also, that's just the fallacy fallacy. This isn't some sort of debate club, it makes perfect sense to discredit someone based on past record. For example I would absolutely take with a grain of salt anything Musk promises. It would be very dumb to just erase any priors everytime someone claims something. And no one does that expect when it's to play fallacy semantics online. I never attacked thunderf00t as a person, I'm attacking his completely bogus track record on SpaceX.
This basically he does every single SpaceX event. I'm not even exaggerating, I'm pretty sure the exact same happened in the latest stream. Just making up stuff about holes, "guaranteed" failures, it's super weird.
The entire video is not the same thing over and over. He lodges specific, credible criticisms of all manner of Musk claims. I think any reasonable person looking at the history of Musks' businesses would come away viewing Musk as a pathological liar, not Musk's critics.
As for the specific quote about laser communications and latency, Thunderf00t's criticism was specifically talking about the latency claims. I actually thought you might be right, but some research indicates that the laser links do not currently provide improved latency, and they are only used when no ground station is available.
I very much appreciate that Thunderf00t does it for every SpaceX event. Someone needs to tell people the truth. I've known Musk was a con artist for decades (since he was fired from Paypal for gross incompetence), but it seems America just woke up to it when he bought Twitter.
I mean, if you ignore the fact that he displays blatant ignorance in the streams he does. And what reports are you referring to exactly?
It has nothing to do with musk, and that's the entire issue. The dude is obsessed with him, clouding anything he says about SpaceX. SpaceX isn't just musk. It's actually super cringe how he seems genuinely mad whenever SpaceX staff celebrates or when a success happens. Or when he literally makes up stuff as he goes while the stream happens ("wow this is super bad, this shouldn't look like this" or even simple stuff like thinking that the water release before launch is for cooling the engines (???))
It's not the first time thunderfoot has obsessed over someone, he used to do the same with Anita sarkeesian. And the same thing happened, it got to the point where it was so weird and obsessive that it made him lose any credibility.
I googled for about 15 minutes for reports about starlink’s lasers and latency and found several articles saying what I wrote above. Feel free to look it up for yourself.
As for his focus on Musk, I feel the same way about that as I did about Carreyrou’s “obsession” with Elizabeth Holmes. Good! I’m glad people are debunking our generation’s greatest fraud (which is Musk. Holmes doesn’t even make the top 10).
I’ve never personally paid a dime for a Musk product, but unfortunately my government has financed his frauds to the tune of tens of billions of dollars. So, I’m glad someone is pointing it out
Edit: I just asked GPT about water sprayed on rockets before launch. It specifically mentioned cooling the engines. I’m not sure what your game is here, but i suggest, like, learning some stuff. I’m tired of fact checking you only to find out instantly that you’re lying. Here’s the text:
Water is sprayed on a rocket before launch as part of a sound suppression system to protect the rocket and the launch pad. The intense noise generated during a rocket launch creates powerful sound waves that can damage the rocket or surrounding structures. Water absorbs and dampens these sound waves, reducing their intensity. Additionally, the water helps to cool the launch pad and the rocket’s exhaust, preventing overheating or damage from the extreme heat generated by the rocket engines during liftoff.
If you’re claiming the guy who started companies that revolutionized two industries is “our generation’s greatest fraud” then you’re a lost cause.
He is prone to very unrealistic timelines and some hype, but at the end of the day he delivers so much that normal people (those without Elon Derangement Syndrome) are happy to look past that.
Some things not working out is inevitable if you have extreme ambitions.
Who fucking cares if the latency isn’t better than fiber, Starlink is providing broadband globally that is orders of magnitude better than previous satellite.
He was confidently dismissive of the entire laser link idea, not just the latency claim:
“Starlink can’t do any of that at the moment. Probably something to with the fact that the satellites are hundreds of kilometers apart and you’re trying to hit a tiny moving target from another moving target and then chaining those together”
That’s in fact exactly what they’re doing now. They just haven’t optimized it enough yet to reduce the total latency.
First of all, no, absolutely no article I've read portray a picture that is even a bit similar to what thunderf00t claimed in that video (especially with regards to bandwidth). It is such a weird argument to fall back on "well ground stations are still needed", as if that was his original claim. The laser interconnects work, and his arguments about alignement/bandwidth/cost were just wrong.
And yes. Even chatgpt says that it is used to prevent vibrations. It could also help cooling the launch pad I guess. But not the engines! That's a completely different thing, the engines get absolutely 0 cooling from the water. The entire point is to allow them to get as hot and powerful as possible without damaging everything around! It's almost entirely for vibration control btw, so any cooling to the launchpad isn't the point. You don't even need chatgpt to know that, it's literally something that a lot of launch platforms have done for decades.
As for frauds, how exactly is SpaceX a fraud? Again, I don't care about musk. I'm specifically talking about SpaceX. And in any case, there is so much legitimate reasons to dislike Musk that it is actually super unhelpful to have personalities like thunderf00t obsessing on something as visibly successful as spacex.
I mean, chatgpt is just wrong. You could've just watched the second link I posted. He says it's to cool the engine. Not sure why you think chatgpt would be good at this, especially when I'm referring to a specific link that you could have just watched?
You could just watch the stream too. How exactly do you think chatgpt would know about a stream that happened 2 weeks ago?
And what was even your prompt?
Look, just because you find some tiny clip in a stream where someone misspeaks (if he even did), that's not all that interesting. As ChatGPT pointed out, in general the guy knows this piece of minutia. You're acting like a conspiracy theorist here.
I get it. You think space "exploration" is super important. I think it's not. You think SpaceX is generating revolutionary progress. I think it's very evolutionary, and that the real reason so little space progress was made for 40 years is because space just isn't a fertile area for doing useful things. You don't appear to want to defend Musk, so there (I guess) we agree: He's a terrible person.
> Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
The SpaceX budget is several orders of magnitude smaller than the Apollo budget. Also, the Apollo era rockets were entirely unable to launch a large constellation like Starlink at reasonable cost like Falcon and Starship.
> Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
Not sure whether you are serious. Assuming you are, what would be the better alternative then?
It's not several orders of magnitude smaller. According to ChatGPT, SpaceX has spent $20-30B as of 2023, compared to $160-170B in 2023 dollars. That's less than one order of magnitude, and consider that SpaceX is starting with all the knowledge gained from Apollo, plus 50 years of technological progress.
To your second question, the better alternative is not to send a bunch of junk into space. Aside from low-orbit satellites, space is a waste of time and a distraction, and increasingly appears just to be a way to trick people into ignoring disastrous fiscal and monetary policies while enriching one person.
Don't cite ChatGPT, it's prone to confabulation. According to Wikipedia:
> At its peak, the Apollo program employed 400,000 people and required the support of over 20,000 industrial firms and universities.
That's far more than the roughly 13,000 SpaceX employees. Moreover, that's just Apollo, there were also related programs like Gemini. (The SpaceX employee number also includes people not working on the Starship program.)
> To your second question, the better alternative is not to send a bunch of junk into space. Aside from low-orbit satellites, space is a waste of time and a distraction, and increasingly appears just to be a way to trick people into ignoring disastrous fiscal and monetary policies while enriching one person.
Even if thats true, who else can launch satellites at SpaceX price and regularity? This is an actual question, when Falcon 9 stage 2 exploded several months ago, my cubesats got delayed
I know several space startups that's currently limited by launch prices
Who cares? Since the 1960s, space launching has never been limited by supply. It's limited by demand. That's why 80% of SpaceX's cargo is for satellites to support their marginally useful Starlink business. Like Hyperloop, "space startups" are just dressed up snake oil.
Imagine if there were hundreds of "startups" aiming to sink stuff for some reason to the bottom of the Mariana Trench. Sure, doing that is difficult and fun to think about from a science fiction perspective, but the bar to show how such a thing could be useful is and should be quite high.
I asked GPT to give me the 5 most compelling space startups created since 2020. Here's what it gave me:
* Space refueling
* Getting things back from space more cheaply
* Removing space debris
* Getting things to space more cheaply
* Microgravity life sciences
Of these, only the last one is an actual product. The others are just picks and shovels for nonexistent products. And, I don't see why microgravity life sciences requires the ability to deploy unlimited quantities of crap to low-Earth orbit.
Oh my good you have really gone deep into the rabbit hole. Sad to see.
> Since the 1960s, space launching has never been limited by supply.
It has been limited by price. Tons of business that now exists could have existed before. There is a whole history of sat companies that went bust, and big reason they did go bust is because the capital requirements were to high.
And even if your statement was true, the only reason it was even remotely true is because things like the Space Shuttle were subsidized by the government at billions and billions of $ ever year.
Now the government doesn't have to subsidize launch anymore.
> That's why 80% of SpaceX's cargo is for satellites to support their marginally useful Starlink business.
4 million subscribers 'marginally useful' ...
> Like Hyperloop, "space startups" are just dressed up snake oil.
Hyperloop was literally just a idea blue paper. Starlink has 400 million subscribers and has had a literal influence in the larges European war in 7 decades. But sure those are comparable. Totally.
> I asked GPT
That you resort to that because you clearly don't know any of the industry yourself is very telling.
Please for the love of god don't look at ThunderF00t. He is literally just a guy who made a job out of farming money from uniformed people who dislikes Musk.
He has no credibility at all, like literally 0. Nobody that follows this topics, even if they don't like Musk or SpaceX consider him reputable.
He is literally a professional hater. He just continually moves the goal-posts to always present himself as 'the reasonable skeptic'.
> Currently, around 80% of SpaceX's rockets are dedicated to launching Starlink satellites.
And the other 20% are still more launches then the whole of the Western world would have had before SpaceX.
SpaceX is simply so fucking successful that you have to totally reconsider how you look at the numbers.
> and things like starship don't really have a reason for existing
And if Starship is cheaper, then Falcon 9, and that's literally the whole reason it exists, then making Starlink and other launches cheaper still makes sense. Stopping innovating because of market share is an idiotic thing to do. Its what people argue who don't understand the difference between absolutes and %.
The market for space launch and space economy will be much bigger in 10-30 years. Now we can argue how much bigger, but its defiantly gone be bigger.
And also, Starship literally needs to exists because the government want's to land on the moon. And using Starship and sharing lots of technology with a launch vehicle that is needed for Starlink anyway just makes a whole lot of sense.
> Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
What an absurd criticism is this? In the 1960 they basically had no regulation, 100% political support and literally unlimited money.
SpaceX had barley any money at all until like 2020 for this project and even then they could only invest a fraction of that into Starship.
If you compare Apollo, the NASA budget was around 20-40 billion $ per year compare to SpaceX who only crossed the 1 billion $ per year in like 2022.
So this is exactly what I mean when I say ThunderF00t has 0 credibiltiy. Nobody should talk arguments like this seriously. Its just arguments from bad faith. I suspect he knows that he is fully of shit, but he has makes a lot of money from continually telling everybody what they want to hear.
> My view is that Tesla, SpaceX, etc. are just cults of personality. Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
ThunderF00t is closer to a cult of personality. He has achieved absolutely nothing, he can't even edit videos as well as most 13 year old on tictac. He is a man in his 40 and his humor is even more childish then that of Elon Musk.
And your claim is simply bananas. Calling landing rockets and Starlink 'non-zero' is the understatement of the century. Starship has literally revolutionized space internet and global connectivity, and literally everybody, including all their competitors and every government in the world understands and reconizes that.
And literally some of the largest cooperations on earth, plus major nations are trying to replicate it. Amazon is investing 10+ billion $. Europe, China, Russia all will try to replicate even part of it, but they all know they can't match it.
Lower LEO internet will basically not go away for the rest of human history, unless civilization crashes or somebody comes up with something even better, but we have no idea what that would even be. But somehow you call it a 'dead end'. What are you even talking about.
I mean seriously, please break out of your bubble and look at the world with objective eyes.
Your claims about the dollar amounts the US government has paid to SpaceX are false. The numbers are much higher than that. Just do a quick search.
It’s completely nonobvious to me what value there will be in massively increased amounts of junk being launched into space in the next 10-30 years as you say.
Maybe Starlink is a good idea, maybe not. I don’t really have an opinion on that, and it’s hard for me to picture why and how they have 4 million subscribers.
But even if it is a good idea, what are the next 10 good ideas? And what use is there in sending stuff and people to the moon and mars? It’s all delusional nonsense.
> Your claims about the dollar amounts the US government has paid to SpaceX are false. The numbers are much higher than that. Just do a quick search.
Can you please be exact on what I am wrong about? I didn't even metion a praticular number, the numbers I mention have nothing to do with how much the US pays SpaceX. The numbers I mention was investment in to moon rocket program.
Total amount paid to SpaceX overall is anyway completely irrelevant. Typical Thunderf00t style obfuscation and confusing spreading.
The Apollo program also didn't include how much money was spent on military payloads, so its again, completely irrelevant in the comparison.
And in your typical fashion, you competently ignored the overall point. Appollo had a far, far, far larger budget then SpaceX ever had and it had if for far longer. Arguing with you is utterly frustrating.
> value there will be in massively increased amounts of junk
Ah the old Thunderf00t moving the goalpost move. I guess humans should never have invented ships, because it massive increases the amount of debris in the ocean.
Also please study orbital dynamics. Starlink itself will leave zero orbital debirs.
> Maybe Starlink is a good idea, maybe not. I don’t really have an opinion on that, and it’s hard for me to picture why and how they have 4 million subscribers.
So because you don't understand how the world works, its everybody else that is wrong. Great attitude to have.
> But even if it is a good idea, what are the next 10 good ideas?
Ah we are moving the goal posts again. I really don't want to have a discussion with you, because whatever I say, you will simply move the goal post again anyway.
There are tons of things humanity already does from space. And we can do those things more and better now. That is already good enough. If you personally don't see the value of any of the things humanity has done in space in the last 80 years, then I can't really help you at this point.
In addition there are literally 1000s of space startups we can have an argument about each one of them. Any that I bring up, you can come up with a bunch of reasons why they aren't actually go ideas and you might be right. But at least I'm not arrogant enough to claim to know if they will work or not.
I used the word "junk" not to suggest we're putting too much debris in orbit. It was to say that this stuff is borderline useless. I did some research on starlink, and it looks like most of their users live in the US and just signed up because our country is so dysfunctional it can't offer fiber to people living in places like downtown San Francisco (!). I guess I wish we'd solve the actual problems here instead of engaging in weird space fantasies.
The tricky parts (that we don't really know as non-SpaceX employees) are:
- how accurate is the clock onboard the satellites? Given that it's likely an OFDM signal the timing is probably pretty good, but given that they're launching zillions of them they probably don't all have atomic clocks onboard
- how accurately is SpaceX tracking their orbits? Kind of a similar answer here... they're doing beamforming to the ground terminals, so it has to be pretty good but we don't really know how good.
- how many SVs are actually visible at a time? We need a minimum of four but the more the better. If there's lots visible we can somewhat work around the first two issues statistically but if there's a limited number than the orbit and clocks need to be super accurate.
Also—how accurately do those satellites track their own position? Unlike the high-orbit GNSS constellations, LEO satellites would bounce around a bit from orbit to orbit, as they're relatively close to the earth and sensitive to uneven distributions of mass. I don't know the exact magnitudes, but I understand they're large by GNSS standards.
Starlink satellites use on-board GPS receivers for extremely accurate (centimeter level) measurements of their position. The orbits which SpaceX reports to the world (for collision avoidance) are based on these measurements.
Most of this article feels like it's discussing irrelevant methods, you only need GPS to get it close (well for what they're doing they don't need GPS at all, though I'm sure it's used), we have much much more accurate ways of measuring the positions of things from a fixed reference point, 0.5cm deviation on your positional measurement is trivially achievable with optical systems. Why is the author spending paragraphs discussing IMU accuracy when we're trying to line up a rocket with a tower. You care about the rocket's relative position to the tower, you can put your measurement equipment on the tower, you don't need to worry about how accurate your accelerometers are.
I assume they are doing something much more clever/hardened, but you can trivially achieve much greater spatial accuracy with a Vive Tracking Puck for like $100.
Certainly lab equipment can measure distances well below 1 um fairly easily, I could manage 1 um in my garage. The issue is that the conditions at time of catch are VERY dynamic and not at all lab-like.
Your positioning system needs to acquire a fix at least 100m out in variable atmospheric conditions on a rocket undergoing heavy acceleration and dumping all kinds of heat, smoke and vibrations into itself, the atmosphere, and everything around it.
In addition having a fix on your tracking device is only half the game, not you have to figure out where the rest of the rocket is in relation to your tracking device. Which again, vibrations, temperature and manufacturing all have an effect.
So while yet, a vive tracking puck isn't entirely unlike the workable solution it is also entirely unsuitable as a solution and should not be used as a baseline to measure off of.
So? Yeah it's a challenging environment, we know that. My point is that the default way to solve this problem is to track your object from your reference point.
Bill Gerstenmaier was talking about the flight test 4 landing accuracy, which landed on the open sea in the Gulf of Mexico, not on the tower like the recent test flight 5. The only thing nearby was a buoy. I'm pretty certain it didn't have advanced laser systems.
The buoys were not trivial devices. See https://x.com/CosmicalChief/status/1626333723514834944
Still, lasers on a buoy?
This is the part about landing a space rocket that you wonder is not technically possible?
Looking at the image I can see a dark device on top of a mast that could be anything electronic.
The buoy is shaking in the water, so it likely can't aim at ship.
There’s a big cross in the middle of the landing pad that you’re trying to aim for - you don’t need advanced laser systems to get an accurate fix on where the landing pad is from the rocket - or where the rocket is form the landing pad for that matter.
> Bill likely misspoke or was talking about control error.
Mixing up control errors with absolute errors is a very common form of miscommunication in robotics.
I work with relatively big robots and often my colleagues would say something like this "During the test we had 0.5m cross track error, so we did X, Y, Z ...".
And I always ask them for clarification. Were they looking at the robot and seeing that it is half a meter off where it should be, or were they looking at a screen and seeing that the robot thinks it is half a meter off from where it wants to be? Because those are two very different situations. And both can be described with the same words. (And sometimes it can be both, or just one of them.)
> or was talking about control error.
Control error is defined as the difference between desired value and measured value. So this is pretty good?
Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.
> So this is pretty good?
Not sure what you are talking about. If you are asking if 0.5cm is good controller error for an orbital class launcher on landing? Yes, it is extremely good. Without doubt.
If you are asking about my tangential story where there is confusion between total error vs controller error then no, it is not good. Confusion is never good. Especially if the system is not within the total error budget. Because to improve it you need to know if you are dealing with measurement error or controller error.
> Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.
Sure. I doubt that their total error is within 0.5cm, but both of their landings were extremely succesfull.
The robot knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation.
Reference: https://www.youtube.com/watch?v=bZe5J8SVCYQ
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...
This voice sounds like something that Mark Farina should be dubbing into his next album. But it's the first time I've heard this bit. Where did it come from? Is this a classic in engineering circles of some shit Rockwell actually sold to the military?
It was already dubbed into a song. https://www.youtube.com/watch?v=_LjN3UclYzU
It's from an old air force training video. Best guess I'be heard it that it's an unsuccessful attempt to explain Kalman filters (or something similar) in layman's terms.
It's definitely floated around for a while, but it grew in popularity in the past few years.
this sounds like it's read directly out of the inscrutable text book for the one control systems class i had to take.
I thought it was a Cave Johnson reference before seeing this.
I think this was called "error.wav" when I first saw it sneaking around a campus network.
> whichever is greater
This always stuck out in an otherwise excellent bit, because you should definitely _not_ be taking the absolute value of your control error.
By this point I automatically even read it by that voice. :P
How does the robot know where it isn't?
this only works if the retroencabulator is properly calibrated.
The article discusses the absolute error coming from RTK systems and claims that it won't be as low as 0.5cm, but surely the relevant metric is relative error, and I can see commercial systems advertising that level of precision.
i.e. the booster doesn't know it's actual position to within 0.5cm but it knows it's position relative to a buoy or the catch arms to that precision.
Rtk already is 'relative' error- it requires one or more base stations (with either known absolute location or assumed one for relative positioning).
But survey grade gnss is a web of rabbit holes, if you want to get into it.
And there are ways to get sub mm accuracy both relative and absolute, but idk of one that would be quick enough for the required reaction time of dynamic landing via 'catching'.
But multi-centimeter (4-5) that's really easily doable is probably good enough for other systems to take over from.
When Tim of EverydayAstronaut quoted this[1], as I recall the quote was within 0.5cm of the target landing site. So I assumed that to be relative accuracy and not absolute.
[1]: https://www.youtube.com/watch?v=pAPt5vbr-YU (don't recall timestamp, sorry)
My lawnmower (openmower) can do <2cm accuracy over GNSS. It is absolutely believable they could achieve 0.5cm on GNSS (plus rtk correction data from a fixed base station nearby) alone without measuring any relative distance using other systems.
I'd love to hear about 2cm accuracy uncorrected. Does it have dual GPS units?
Well, it isn't "uncorrected". It's just that you don't need any additional hardware other than a second gnss receiver on the base station and some kind of link between them.
GNSS is more than accurate enough once you know all slight errors in satellite orbits and the atmospheric distortions currently affecting the area near the base station and can correct for them.
It's significantly more difficult to actually land a jumbo jet sized rocket booster with that precision than to measure its own relative position. Gerstenmaier was talking about landing accuracy. My guess is that measurement accuracy is a red herring. More likely it was a slip of the tongue (the good man is 70 years old) and he meant to say it landed with a 0.5 meter, not centimeter, accuracy relative to the buoy.
I'd be very interested in the systems advertising that! I have not seen that even for stationary surveying equipment. I think it's also important to distinguish between RMS error which is often the better topline spec that companies give you, vs the 95% confidence error which is the more relevant one for flight reliability.
In the specific case of a docking-type manoeuvre presumably you only need the highest accuracy when you're getting very close to the target.
No reason you couldn't use RTK GPS for <10cm accuracy for most of the flight, then in the last few meters of landing switch over to to high-precision, short-range tracking - like optically tracking a marker on the grabbing arm.
For other specific cases - like bridge monitoring - there are reports of 2–3 mm precision [1]. Of course, bridge monitoring has quite distinctive requirements; a 5Hz vibration component and a 0.0001 Hz thermal expansion component. So there's a lot of potential to average over lots of readings to reduce noise.
[1] https://www.sciencedirect.com/science/article/abs/pii/S02632...
If you want to land 99.9% of the time, it really is te 99.9% circle you should be looking at...
Or in fact, you need even better than that, since you don't want your whole error budget used up by the GNSS system.
What's absolute position? Isn't all position relative?
https://www.youtube.com/watch?v=bZe5J8SVCYQ
Either I'm very stupid or that video is some kind of epic trolling.
Epic trolling, you're sane.
Absolute position is global lat/long coordinates. Relative position is “I’m 0.5cm from the middle of the peg.”
Global lat/long coordinates are defined in terms of coordinate systems like WGS84 or ITRF2020, which are themselves the result of relative measurements between reference stations.
The earth's crust floats on top of liquid rock. This matters at relevant length and time scales; in most places, these effects alone are on the order of millimeters per year. One reason why it's better to use NAD83 over WGS84 in North America is that NAD83 latitudes and longitudes move with the North American plate.
Positions _are_ relative, and the closer you can put your datum, the less drift you'll accumulate.
There is a literal, autistic sense in which you are correct. But there is a practical, pragmatic distinction between measurements that we call absolute versus those we call relative, and pedantic correctness misses the point.
I found this video from the perspective of a landing pin interesting, especially when played back at low speed: https://youtu.be/ExV6PHRM8eI?t=17
You can see the arm comes in, then there's some side-to-side bounce (not sure how much is the rocket bouncing off vs. the arm fine-tuning its position). Just after contact seems to be made, and before the shock absorbing (or yaw-correcting) pistons drop much, there's a large flash from the engine. Is that a characteristic of engine shutoff, or was there a last-second "hover" push just before shutoff and drop? I wonder how much force the arms felt.
Another perspective showing both arms, and (as mentioned in the article) how the left one adjusted more significantly at first: https://youtu.be/JlcrNakUGVs?t=3
Worth noting that the grid fins are about 15 feet long, and the landing pins probably 2-3 feet.
https://nextbigfuture.s3.amazonaws.com/uploads/2023/12/Scree...
Just a few years ago, it was a huge leap just have a rocket return and land, now we're pushing the actual accuracy of how well it can land?
Anybody else thinking this quite the time to be alive?
Well, to be fair, the engineers working on this system have been thinking about the accuracy this whole time even if you haven't. Even on the first go, it still had to land on a relatively small pad floating in the ocean.
The fact that someone tried is significant. We've had 50+ years of not trying.
As impressive as the space efforts in the 60s and 70s were, I've often thought that they were a false start created by a war-like impetus to show off. Tech-wise, we really weren't ready for a space age. The sort of control systems that make this sort of outcome possible haven't been around for all that long, really, especially if you mark them from being economical and not just "it technically existed in a lab somewhere". Plus if you really dig into how these rockets are built and maintained, you see a lot of other technologies that have not been around for that many decades, like, practical and reliable 3D printing, and computing simulations that have more computational power per second than the entire computing world could scrape together in a year in the 1960s, and those are just the highlights, not the exhaustive list.
A lot of people are like "we got to the moon in the 1960s, where's the progress we should have had since then?" but I see the 1960s as the bizarre exception rather than the thing that should be used to set the rule. There was no way the space age was going to happen then, in an era where you're almost sitting there counting each bit of RAM you can afford to send into space. The true Space Age is just dawning now, and it's still early in the dawn; we still have to have massive international cooperation to put a single space station up, we can't do something as basic as refuel in orbit, we just barely started having people in space for commercial rather than governmental reasons... it's just the beginning.
I think it's not so much that we weren't ready for a space age tech-wise, but that the the reason we have so much of our technology today is because of investments made in the 1960s. NASA had basically unlimited money to throw at every technical challenge in the way of landing a human on the moon.
The apollo program drove the need for more computational power, more memory, better guidance and navigation and control systems, better materials, experiments to better understand many phenomena, etc. And after the apollo program ended, the contractors that developed those technologies on NASA contracts could just commercialize them. And the data from experiments, on materials, aerodynamics, combustion, and so on, that is publicly available has made engineering so much cheaper and easier.
I think the 60’s showed how much humans can achieve in terms of innovating with very little (in terms of tech). Now, we’re seeing how much can be achieved with a whole lot more. And, I agree, the space age really does feel like it’s only just heating up. Very exciting time!
> There was no way the space age was going to happen then, in an era where you're almost sitting there counting each bit of RAM you can afford to send into space.
And yet, they got to space. Better computers are not the solution to every problem. And it wasn't a false start. We are already in a space age, we have been for quite a while. It didn't stop at Apollo. We have satellites for the military, TV, weather, various forms of communication, navigation (GPS...), telescopes, space stations, probes and rovers. We do science, commercial and government operations. Starlink is great, but it is just the continuity of all the space communication abilities we developed over the years.
I think computers are not what will enable the "true space age". Sure, they help, and SpaceX, if successful with their Starship will certainly be a big advance, but I think that we are missing a key ingredient to reach the "true space age" and it is nuclear power. Starship maybe could get us a settlement on Mars with hundreds if not thousands of launches and refueling missions. Project Orion was to launch an entire colony in one go, return trip included. Even Saturn was considered feasible. Project Orion is mad, but it goes to show how limiting chemical rockets are compared to nuclear.
And it is something we probably could have done already, without modern computers and 3D printing, if we wanted to. It is maybe a good thing that we didn't though. Spreading radioactive material in the atmosphere and mass producing thermonuclear bombs is kind of scary.
Literally decades of missile / guided bomb development placing warheads within cms of their target.
Armchair aerospaceing here, but it feels like he's a whole class of positioning sensors in this analysis. It seems to be you only need GPS and related absolute positioning systems to get you close to the tower. At that point, what you care about is the relative positioning of the tower and the booster. I would think this can be done very accurately with a host of options: cameras, radar, lasers, ILS style systems, etc, etc.
Right? They land fighter jets on carriers with a light signal that projects out from the ship at a particular angle. It seems very easy to do something like this with some form of electromagnetic radiation. Or have some way for the tower to detect the exact position and communicate with the rocket.
I understand engineering is complicated but this honestly seems like the easiest part of the problem to solve.
It's more likely that SpaceX determined they didn't need super tight tolerances and called it a day.
Carrier landings are accomplished using a combination of indications, and the meatball is only one of three primary tools. If you are not flying an on-speed angle of attack AND lined up on the centerline of the landing area, the meatball position is invalid to a degree proportional to the degree to which those other inputs are off.
The meatball Fresnel lens is canted slightly side-to-side, and only places the hook in the right spot at a given angle of attack. Which is a design compromise necessitated by having to allow multiple types of aircraft with multiple hook-to-eye distances to land on the same aircraft carrier while using a visual input in one location (the cockpit) to properly place a device in another location (the hook point) with high precision.
Source: I've done it.
So just as it is not "very easy" to trap on board the boat with "just" a light signal, I would assume landing a building-sized booster has a similar if not bigger list of potential "gotchas."
Very easy compared to all the other hard problems SpaceX has to solve, yes.
> SpaceX determined they didn't need super tight tolerances and called it a day
Yup! This is my conclusion in the article - the landing box for the Super Heavy booster is 5x13x18 meters on each side, with 5-15 degrees of angular tolerance in each of the vehicle axes. So the margins are big enough that you don't need millimeter level precision for the rocket position.
> Could you use other real-time distance measurements like laser rangefinding or visual processing? I don’t think so
This is the part I question though. Seems like an org as well motivated as SpaceX could easily solve that if it was necessary.
My take is that it would probably be possible with enough effort, but there isn't an easy solution. And if you don't need it then the best part is no part. :)
I suspect the real problem is wind. A last moment gust could push the booster far enough away that it cannot recover.
This is fixable by setting wind and gust limits for recovery, just like every other aircraft on the face of the earth.
I'm sure they've done that. But the wind is a chaotic system, and once the booster has begun its descent it's committed regardless of wind changes.
There have been many airplane crashes because of sudden unexpected wind changes while landing.
Does SpaceX even use traditional GPS? I'd assume with something like Starlink they would be able to employ something more precise/fit for purpose.
GNSS RTK is incredibly accurate these days. By the time that you're close enough to the landing zone, you're close enough to get positioning down to centimeters on consumer grade hardware, which the article points out.
The actual question is literal: Can SpaceX land a rocket with sub 1 cm (1/2 cm) accuracy? GNSS RTK can get you down to a couple of centimeters, but getting more granular resolution than this isn't reliably possible with current professional grade technologies.
I'm personally unsure if the military has greater resolution than what's possible with RTK or w.r.t. military use GPS, but I would not be surprised if they did. If that's the case, NASA would most likely have access to it, I would assume. But the article specifically calls this out saying that it's not accurate enough to surpass the resolution of using RTK.
What's really cool about these questions is that the same problem space is applicable to self-driving cars and SLAM, if you're into that sort of thing. Lane detection, etc.
>you're close enough to get positioning down to centimeters on consumer grade hardware
But in realtime? (single-digit second latency, at least)
Yes, for the purposes of landing speeds. In fact, at vertical aircraft landing speeds, your time-step to position Δ is more accurate than automotive SLAM.
Nice, TIL. Thanks!
I mean rtk accuracy is considering rtk in isolation. You can get better accuracy if you combine rtk with other methods such as an IMU.
Depends on what you define as 'traditional': basically if you want positioning information via GNSS, the techniques for getting a better reading a fairly well understood, and it doesn't really matter how good your satellites are, the atmospheric distortion is the issue and you need to model and compensate for it by measuring it with a near-enough base station, using multiple frequencies and constellations, and if you're moving, an IMU to constrain your motion over as long a period as you can to effectively average out the other noise sources. Half a centimeter, given all of the above, is better than what I've seen quoted in the space, but not utterly crazily so.
Wow, I can’t believe I never realized that SpaceX could sell access to a positioning system far better than GPS…
Not really, the Gyros described in the post are also essential. If you don’t know the attitude of the vehicle, you can’t point the engines in the direction your control algorithm says you should to hit the target.
Edit: I think I misunderstood the comment. Yes, you can use the absolute methods for rough guidance and then use relative positioning for the final approach. The article has a line about why the author doesn’t think that’s likely though.
Maybe if the rocket knows where it is because it knows where it isn't.
That is what they told us in missile maintenance school.
And gyros have gotten a lot better. Especially if you're throwing money at the issue like you know those folks are.
0.5cm isn't even well defined, considering that the rocket itself is probably out of round by larger tolerances, not to mention issues of thermal expansion.
I would suspect it's some average of many points that the control systems try to track, because the rocket is not a point, and the press wants to quote a single easy number.
I'd expect that the rocket has a ton of sensors, and a ton of passive and semi-active tracking devices all over the body.
E.g. I'd put a bunch of NFC-type responders in a number of key positions, responding at different frequencies. Then a typical sweeping-frequency radar pulse would activate them all, and the response time and the Doppler shift would tell about positions and speeds of many points on the rocket. I'd do a similar thing with reflectors and IR/optical tracking.
All these points should follow some reasonable trajectory for some point the top of the rocket, near the chopsticks, would move towards some desired catch location point. Probably this motion is where "with precision of whatever cm" relates to.
Yup it's surface amplitude with the engines running is probably more than that.
is "surface amplitude" vibration? I could see vibration being graphed over time as a wave with an amplitude and frequency. I can't really comprehend the size of super heavy combined with the energy density of just one turbo pump on one raptor engine (let alone 33x2) and then the precision of control needed to catch the whole thing with chopsticks. Not many things do i admit are just beyond me period but this is for sure.
/raptor 3 pumps look like you could hold them in your hands but iirc they deliver over 100k horsepower each.
The larger size makes control much easier.
It's probably defined by the catch points as that's what matters: whether the catch points end up where they belong (good) or not (disaster). The catch points are not "out of round".
That's worse, considering that the control points are a huge distance away. Just flex alone has to be huge.
I should have mentioned that the catch points are on one long bar that goes atop the booster. They are not simply attached to the sides of the booster. Booster shell flexing does not affect the catch points at all.
A lot of people think it landed on the large grid fins, this is not true it actually landed on much smaller landing pegs
This is more or less easy to see depending on the video you watch. Here's a good one that demonstrates it very clearly.
https://www.youtube.com/watch?v=ExV6PHRM8eI
I was impressed before. Now I'm doubly impressed after having watched that. Thanks.
This is even more mindblowing than landing on the fins. Amazing.
Landing on the grid fins would be a really bad idea. Even though they're car-sized, they're not load bearing and "only" made of steel (not titanium etc. .. just yet). Starship's Raptors blast during hot staging is enough to bend them on the top. https://www.reddit.com/r/SpaceXLounge/comments/1g3bi7s/grid_...
Though the original plan was indeed to land it on the (reinforced?) grid fins: https://x.com/elonmusk/status/1344327757916868608
I actually think there is some old Starbase tour interview where a SpaceX guy implied it was Musk's idea, though I could be misremembering. Catching the booster kind of makes sense, since they needed the tower arms anyway for stacking and unstacking.
They need to be able to handle some forces but indeed likely not an equivalent of half or even quarter of the booster landing weight.
Interesting, are there more than 4? because I was also amazed that the rocket was rotated at exactly the right angle to be caught by them. But maybe that is the 'easier' challenge when you are hovering with such accuracy.
I keep finding myself watching the catch every few days, and it does not tire to impress.
> I think < 10 cm accuracy is achievable
If you don't know how precise GPS receivers can get with dead reckoning techniques, this demo of someone "drawing" onto a map of their driveway using a GPS receiver is very impressive: https://youtu.be/3tQjIHFcJVg?t=245
It looks like they're getting measurements that are only a few inches away of the module's real position, although of course the conditions seem favorable with an unobstructed sky and consistent alignment.
The module they use is a ZED-F9P by u-blox. I've used ~$50 u-blox GPS modules in DIY electronic projects before since they're often the brand you'll get when buying GPS modules, but this particular type with dead reckoning is much more expensive. Sparkfun has it for $275 for example: https://www.sparkfun.com/products/16481.
I believe this is demonstrating the performance improvement of RTK [0] alone, not dead reckoning. GPS + dead reckoning is what phones and wearable do afaik, whereas RTK requires getting correction data associated to base stations nearby and seems mostly relevant for industrial applications (you need a subscription in the case of u-blox).
[0] https://en.wikipedia.org/wiki/Real-time_kinematic_positionin...
You can do even better with radar. If you place a set of radar reflectors around the tower at known locations, then you can detect them from the booster and triangulate the distances to a precise position. Plus, radar gives you relative velocities, so your speed and roll rate estimatimates get even more precise. I bet you could get down to millimeters with a setup like this.
Is this really viable given all the electromagnetic interference the rocket motor exhaust plumes are generating?
Falcon-9 uses radar altimeters for determining vertical "distance to go" during landing.
While a sideways position error of even ten meters is not fatal, it is critical for the rocket to be quite close to zero altitude when deceleration brings the velocity to zero. (Any residual error must be dealt with by the shock absorbers, and their capability is modest.)
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As the article explains, with a well designed procedure, the required navigation accuracy is quite modest. Even the latest consumer IMUs and GPS would do, and SpaceX is using even slightly more accurate "tactical grade" units, typical for all launch vehicles.
Good article. It is nice how it goes through all the points systematically.
There is also an interesting analysis about the control engineering perspective:
https://youtube.com/watch?v=QHikx6kVvAo
It talks about how real time control system algorithms work with algorithms like like PID and MPC. I assume the SpaceX solution is likely one of the most advanced control systems in the world.
It is great that the author of the video helps to introduce the topic to the general audience. This is a vast and a fascinating subject with lots of material available for a further more systematic study.
It becomes more technical, if one is specifically interested in the methods used by SpaceX. But there are some overviews that describe the general idea. Here is one presentation by Behçet Açıkmese: https://nescacademy.nasa.gov/video/eda2b96bddf945629be2c9d2e...
Note that before joining SpaceX to lead their autonomous landing software development, Lars Blackmore worked at JPL, where together with Behçet Açıkmese they developed the autonomous precision landing algorithms based on real time optimization methods. So, even though SpaceX has undoubtedly developed additional nuances to match their needs and capabilities, they were building on this prior work at JPL.
It's interesting that NASA, despite working on control algorithms, apparently didn't consider using them for building a reusable rocket. (SLS isn't planned to do a propulsive landing, and neither was its predecessor Ares V.) Though they probably did use them to some extent for the "sky crane": https://en.wikipedia.org/wiki/Sky_crane_(landing_system)
Making any kind of a rocket that works is already nontrivial (once one goes beyond Estes models), but in terms of complexity of the challenge, making some kind of a hopper that goes up and down is a task that ambitious amateur groups with a few members and under $1M in funding were demonstrating even before SpaceX was founded. There is no need for a highly efficient engine, there is no need for lightweight structures. Many other concerns, such as low frequency structure oscillations, aerodynamics, etc are practically nonexistent.
Making a space launch vehicle is a task for a group with at least x100 more resources and experience. Reaching orbital velocity is pretty hard. Most startups do not succeed.
Making a space launch vehicle which does not spend the fuel entirely, while carrying extra hardware to also land after the launch is another step up in how hard this is. Very serious institutions worked on this problem since 1970s but lots and lots of people were skeptical. Shuttle was impressive, but also very expensive. Then SpaceX has shown that it was not only possible, but even practical to make ordinary rockets reusable. That was amazing. Even now, almost a decade later, nobody has shown anything like that -- though a number of Chinese startups are working on it.
> Half a centimeter landing accuracy is not possible, and Bill likely misspoke or was talking about control error.
Maybe the 1/2 cm accuracy refers to the final position of the booster's catch points on the arms after they've closed, after the booster's engines are off, and after the booster settled, and maybe they mean lateral accuracy. I would forgive them for that because that's the accuracy that actually matters here.
If the catch points were off then that might spell disaster, so the catch points' landing accuracy including the help of the catch arms is what matters.
The catch/lifting points may look small, but actually protrude from the side of the booster by 2-3 feet. Note that the booster is actually in a hover at the point the arms close in to touch it, so as long as it's vertical rotational axis is right (there are only 2 pins - one on either side), the positioning of the pins on the catching arms is basically guaranteed.
Right, so if SpaceX meant that they had an error of only .5cm maybe they meant that the error on the booster rotation angle was small enough to produce only a .5cm error at the catch points. Since they weren't specific, it's hard to know what they meant.
The booster rotation angle error and the catch point placement error were much too small to detect with the naked eye on the published videos. Every other measure of accuracy was clearly within tolerances -- and also hard to discern with the naked eye.
As amazing as .5cm accuracy sounds, if SpaceX meant catch point placement error, then it's quite as impressive because that only implies everything was within tolerance _and_ only the booster rotation angle error need have been impressively near-zero measure. That's... still amazing, honestly. If you can get the booster rotation angle error near zero then you can get the other errors way down too.
Rocket alone need not be this accurate as grabber arms should also do some maneuvering to get the final accuracy.
You can see the landing arms adjusting in the video as well.
His choice of stainless steel is panning out well here - I doubt if aluminum or composite body structure would hold up as well to the "grab" forces from even minor misalignment. A composite structure would likely be entirely compromised by a big scrape.
It would be interesting to see a test where the landing speeds were deliberately too high - how much deceleration can the arms handle safely?
I think the chopstick mechanism is probably the best possible catch mechanism for such a tall object. The booster will be suspended from the top, which means the booster isn't subject to tipover as it would be if landing legs were involved. We've already seen this many times in the Falcon 9 booster series.
I can't see chopsticks ever working from a droneship, though - too much induced rotation for chopsticks to compensate.
As an alternative to chopsticks, a catch 'sleeve' might be possible, though it would magnify alignment errors considerably.
I would have thought the vibration from the engines would produce error of greater that 1/2 cm. Still, it seamed to have worked well. So, there you go.
I feel like he's limiting himself to just 2 positioning methods.
There are so many other methods that the lander can use to know where the tower is.
Yes, that seems like a very big hand-wavy assumption. This paragraph is quite...something:
> Could you use other real-time distance measurements like laser rangefinding or visual processing? I don’t think so – the surface of the vehicle is too irregular to get a reliable fix point, especially while it is moving, and these are vulnerable to smoke/fog/gas/ambient lighting. Technologies like Ultra Wideband are vulnerable to multipath reflections and attenuation by the booster’s steel walls, and aren’t more accurate than RTK anyway.
That is not exactly an exhaustive list of methods to locate an object.
I have no idea whether 0.5 cm precision is feasible or even needed, but this part felt a bit off.
I vaguely remember Musk talking about reflective paint for some band on the landing pad of Falcon, a long time ago.
> At the most precise, an RTK positioning system could lower position accuracy all the way down to 2.5 cm (+1cm per km of distance). If SpaceX put a receiver on the launch tower or the ocean buoys, then the landing position could be incredibly accurate. But even the most advance positioning tech won’t guarantee it down to 0.5 cm. And RTK does rely on being able to acquire and maintain a link between the booster and ground for this precision.
I don't understand this last sentence. Afaik RTK correction only requires receiving correction frames on the booster's side, which can be distributed via l-band just like GPS. I suspect the latency constraints are also quite low as the conditions aren't going to change quickly near the tower with the kind of good weather they choose for launch.
If it's positioning relative to the chopsticks, I'm sure it's possible to know where you are within a centimeter, even with all the rocket exhaust flying around. That's what DGPS is all about.
It's still wildly un-nerving to me that there's no publicly stated option other than the chopsticks for landing(edit: some future passenger craft). Imagine if you've got enough fuel to avoid slamming into the ground, and a nice big ocean, or a lake sufficiently deep... couldn't a water landing happen and let future passengers survive?
This is not the passenger vehicle. That's the second stage, this is the first stage booster. They've also landed the second stage but that did a water landing from orbit which in many ways is even more impressive.
I think they were simply speaking of the final pads the rocket rests on top of the chopsticks have 5cm of error either direction.
But judging from the bouncing the rocket did when in the chopsticks the error for positioning into the initial catch position is much larger in all directions. The chopsticks coming closed around the rocket do the heavy lifting for final alignment to that 5cm I imagine.
And here is me trying to find sheet metal fab that could make a simple enclosure that matches the design and is not warped or scratched.
Impossible apparently.
Most hackerspaces have a laser cutter strong enough for a few mm of steel sheet. So chances are, you could make it yourself.
I suspect that finding a proximate hacker space, let alone one with such equipment, is even more of a challenge.
Cuts are not too much of a problem, but bends.
> And RTK does rely on being able to acquire and maintain a link between the booster and ground for this precision.
There are cameras and other electronics sending telemetry (via at least Starlink) on the things.
The "acquire and maintain a link" seems to be a very solved problem.
I wonder how much of a problem crosswinds are. Not a lot of mass, and that big can has a lot of sail area.
From what I understand this is the primary difference and problem with Falcon 9 vs. Super Heavy.
From the Article:
"Why can't SpaceX do a catch with a Falcon 9?
-It does not have separate landing propellant tanks, so propellant slosh will disturb its trajectory. The Super Heavy booster has dedicated central header tanks for landing propellant, so there should be minimal propellant slosh to disturb the vehicle attitude.
-It lands with a single engine which cannot throttle low enough to hover the vehicle, and as such must perform a “hoverslam” maneuver to bring the vehicle to a stop right on the ground. While the Super Heavy booster must perform most of a hoverslam maneuver to slow down just before coming in to the tower, it can hover for the final fine positioning.
-Because it lands with a single engine, roll control is minimal close to touchdown when the airspeed is low and the grid fins can impart minimal torque, and is limited to its weaker cold-gas thrusters. The Super Heavy booster can control roll with its 3 engines all the way to the ground.
-Falcon 9 has no engine-out capability for landing. SpaceX has not confirmed it for the Super Heavy booster, but I believe one engine out is likely possible (more on this later).
-It is smaller with a lower moment of inertia. Rockets get more stable and easier to control the larger they are, much like it’s easier to balance a broom on your finger than a pencil.
-It is smaller, and so thanks to the cubed-square law has a higher area:mass ratio. This means that it will be more affected by wind gusts that might blow it off course."
The designers of the raptor engine should get a Nobel prize in chemistry for combustion physics.
The key was the full scale combustion simulator software that SpaceX developed to design the Raptor.
This talk was given at NVIDIA GTC 2015 and inspired me to go into manufacturing
https://www.youtube.com/watch?v=vYA0f6R5KAI
title: "GPUs To Mars: Full Scale Simulation of SpaceX's Mars Rocket Engine"
This talk is FANTASTIC and has been an inspiration for me for years as well. Highly HIGHLY recommend it.
The accuracy that counts is for the gap between the arms and the booster, which could well be 1cm since they can measure that with sensors as the booster descends between the arms, and the arms can be controlled accurately.
I wonder if they will paint pin alignment marks on the grabber arms?
If they did that and hit them consistently.. talk about rubbing salt in the wounds of the rest of the industry. It would be like a sports team running up the scoreboard on an obviously beaten opponent. Super heavy hitting X's painted on the chopsticks right in the middle would be border line unsportsman-like heh.
Given the size of the booster, what corrections would placing GNSS sensors in multiple places provide to increase positional accuracy?
Eg if you space sensors 20m’s apart.
It’s a really good idea! Unfortunately not too much, since the error is largely from atmospheric distortion of the signal and so the error for two receivers close by would be correlated. You’d need the error to be uncorrelated to gain accuracy with multiple receivers.
Not a US taxpayer, so I don't really have a stake in this, but I'm curious as to where SpaceX spending is compared to their NASA contract milestones.
NASA own estimation is that is only funding about 50%. They mentioned that SpaceX is matching their contribution.
But of course this ignores that before the contract, SpaceX had already been working on this for many years. Raptor development began in 2014ish.
I would estimate SpaceX pays more then 50%. By reports they are currently investing like 1.5 billion $ a year. And the government contract can't finance half of that.
Also, of course in all of NASA history, this is the first time that anybody ever expected to invest themselves. The idea that a company would spend so much to build a moon lander for NASA is not something that was even an option a few years ago.
So why should tax payers be angry even if NASA paid 100%. Unless of course people are just angry that the space program exists at all.
Take a look at videos on YouTube by ThunderF00t. SpaceX is pretty problematic. Currently, around 80% of SpaceX's rockets are dedicated to launching Starlink satellites. This is because they've already soaked up all the demand for satellite launches, and things like starship don't really have a reason for existing. Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
My view is that Tesla, SpaceX, etc. are just cults of personality. Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
Thunderf00t has basically 0 credibility when it comes to SpaceX. He predicted that starlink couldn't ever work, for example. In fact, he even thought that this landing would fail.
Like he might have good point hidden somewhere, the issue is that we know that he will reflexively "debunk" anything SpaceX does, and predict failure every time. Meaning that his takes on SpaceX are beyond useless.
https://www.google.com/search?q=ad+hominem+attack
Edit: Just out of curiosity, I looked up his video about Starlink, and his point was it's a bad business, not that it's physically impossible to do it:
https://www.youtube.com/watch?v=zaUCDZ9d09Y
I'd actually love it if you could find a single thing he says in that video that's provably false. I'm quite confident history will judge Elon Musk properly, as the "Too Big To Fail" version of Theranos and Elizabeth Holmes.
Talking about someone's track record of predictions is not an ad hominem, in the context of evaluating their credibility with respect to the subject of those predictions.
Actually, it is. From the dictionary:
An ad hominem attack occurs when someone attacks the person making the argument rather than addressing the argument itself. For example, saying "You're always wrong, so you're wrong about this too" without addressing the current claim would be ad hominem.
That's exactly what the person I responded to was doing.
Claim:
> Take a look at videos on YouTube by ThunderF00t. SpaceX is pretty problematic.
Response:
> Thunderf00t has basically 0 credibility when it comes to SpaceX. He predicted that starlink couldn't ever work, for example. In fact, he even thought that this landing would fail.
You’re claiming Thunderf00t is a good resource on SpaceX. The response gave examples of how he’s been consistently wrong.
That is not an ad hominem attack.
Actually both the examples you cited are misrepresented. But whatever. You're in the cult. I get it.
And you’re in the other cult ¯\_(ツ)_/¯
>They claim they're going to get these laser communications between the satellites which will make things faster for a long distance... [this is because light travels faster in a vacuum than through fiber optic cable you up to London a very important one for the Global Financial system Starlink latency is under 50 milliseconds while the current Internet is around 70 milliseconds] yeah Starlink can't do any of that at the moment.
>Probably something to do with the fact that the satellites are hundreds of miles or kilometers apart and you're trying to hit a tiny moving Target from another moving target with a laser and then and chaining those together that doesn't sound very easy but they're promising to launch some satellites that can do it in the next generation [getting close to launching satellite 1.5 which has laser interest satellite links]
>Now where have I heard that before... Let's just call me skeptical on this one
https://youtu.be/zaUCDZ9d09Y?t=1688
This entire video is just the same thing over and over. As is usual with him, he doesn't actually make any strong enough claim and just goes on endless sneering. But in the context of the video, it is absolutely clear that he's saying it is just another lie and that it's basically impossible. Remember, this was mere months before the laser network went up. He also claimed that the bandwidth is never going to be usable, but it absolutely is.
Also, that's just the fallacy fallacy. This isn't some sort of debate club, it makes perfect sense to discredit someone based on past record. For example I would absolutely take with a grain of salt anything Musk promises. It would be very dumb to just erase any priors everytime someone claims something. And no one does that expect when it's to play fallacy semantics online. I never attacked thunderf00t as a person, I'm attacking his completely bogus track record on SpaceX.
This basically he does every single SpaceX event. I'm not even exaggerating, I'm pretty sure the exact same happened in the latest stream. Just making up stuff about holes, "guaranteed" failures, it's super weird.
https://youtu.be/OCUceQzCh-Q
The entire video is not the same thing over and over. He lodges specific, credible criticisms of all manner of Musk claims. I think any reasonable person looking at the history of Musks' businesses would come away viewing Musk as a pathological liar, not Musk's critics.
As for the specific quote about laser communications and latency, Thunderf00t's criticism was specifically talking about the latency claims. I actually thought you might be right, but some research indicates that the laser links do not currently provide improved latency, and they are only used when no ground station is available.
I very much appreciate that Thunderf00t does it for every SpaceX event. Someone needs to tell people the truth. I've known Musk was a con artist for decades (since he was fired from Paypal for gross incompetence), but it seems America just woke up to it when he bought Twitter.
I mean, if you ignore the fact that he displays blatant ignorance in the streams he does. And what reports are you referring to exactly?
It has nothing to do with musk, and that's the entire issue. The dude is obsessed with him, clouding anything he says about SpaceX. SpaceX isn't just musk. It's actually super cringe how he seems genuinely mad whenever SpaceX staff celebrates or when a success happens. Or when he literally makes up stuff as he goes while the stream happens ("wow this is super bad, this shouldn't look like this" or even simple stuff like thinking that the water release before launch is for cooling the engines (???))
It's not the first time thunderfoot has obsessed over someone, he used to do the same with Anita sarkeesian. And the same thing happened, it got to the point where it was so weird and obsessive that it made him lose any credibility.
I googled for about 15 minutes for reports about starlink’s lasers and latency and found several articles saying what I wrote above. Feel free to look it up for yourself.
As for his focus on Musk, I feel the same way about that as I did about Carreyrou’s “obsession” with Elizabeth Holmes. Good! I’m glad people are debunking our generation’s greatest fraud (which is Musk. Holmes doesn’t even make the top 10).
I’ve never personally paid a dime for a Musk product, but unfortunately my government has financed his frauds to the tune of tens of billions of dollars. So, I’m glad someone is pointing it out
Edit: I just asked GPT about water sprayed on rockets before launch. It specifically mentioned cooling the engines. I’m not sure what your game is here, but i suggest, like, learning some stuff. I’m tired of fact checking you only to find out instantly that you’re lying. Here’s the text:
Water is sprayed on a rocket before launch as part of a sound suppression system to protect the rocket and the launch pad. The intense noise generated during a rocket launch creates powerful sound waves that can damage the rocket or surrounding structures. Water absorbs and dampens these sound waves, reducing their intensity. Additionally, the water helps to cool the launch pad and the rocket’s exhaust, preventing overheating or damage from the extreme heat generated by the rocket engines during liftoff.
If you’re claiming the guy who started companies that revolutionized two industries is “our generation’s greatest fraud” then you’re a lost cause.
He is prone to very unrealistic timelines and some hype, but at the end of the day he delivers so much that normal people (those without Elon Derangement Syndrome) are happy to look past that.
Some things not working out is inevitable if you have extreme ambitions.
Who fucking cares if the latency isn’t better than fiber, Starlink is providing broadband globally that is orders of magnitude better than previous satellite.
He was confidently dismissive of the entire laser link idea, not just the latency claim:
“Starlink can’t do any of that at the moment. Probably something to with the fact that the satellites are hundreds of kilometers apart and you’re trying to hit a tiny moving target from another moving target and then chaining those together”
That’s in fact exactly what they’re doing now. They just haven’t optimized it enough yet to reduce the total latency.
First of all, no, absolutely no article I've read portray a picture that is even a bit similar to what thunderf00t claimed in that video (especially with regards to bandwidth). It is such a weird argument to fall back on "well ground stations are still needed", as if that was his original claim. The laser interconnects work, and his arguments about alignement/bandwidth/cost were just wrong.
And yes. Even chatgpt says that it is used to prevent vibrations. It could also help cooling the launch pad I guess. But not the engines! That's a completely different thing, the engines get absolutely 0 cooling from the water. The entire point is to allow them to get as hot and powerful as possible without damaging everything around! It's almost entirely for vibration control btw, so any cooling to the launchpad isn't the point. You don't even need chatgpt to know that, it's literally something that a lot of launch platforms have done for decades.
As for frauds, how exactly is SpaceX a fraud? Again, I don't care about musk. I'm specifically talking about SpaceX. And in any case, there is so much legitimate reasons to dislike Musk that it is actually super unhelpful to have personalities like thunderf00t obsessing on something as visibly successful as spacex.
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I mean, chatgpt is just wrong. You could've just watched the second link I posted. He says it's to cool the engine. Not sure why you think chatgpt would be good at this, especially when I'm referring to a specific link that you could have just watched?
I watched the second link you sent me. It cuts between clips ever 0.5 seconds or something. I have no idea what he actually said. I believe GPT.
You could just watch the stream too. How exactly do you think chatgpt would know about a stream that happened 2 weeks ago? And what was even your prompt?
Look, just because you find some tiny clip in a stream where someone misspeaks (if he even did), that's not all that interesting. As ChatGPT pointed out, in general the guy knows this piece of minutia. You're acting like a conspiracy theorist here.
I get it. You think space "exploration" is super important. I think it's not. You think SpaceX is generating revolutionary progress. I think it's very evolutionary, and that the real reason so little space progress was made for 40 years is because space just isn't a fertile area for doing useful things. You don't appear to want to defend Musk, so there (I guess) we agree: He's a terrible person.
> Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
The SpaceX budget is several orders of magnitude smaller than the Apollo budget. Also, the Apollo era rockets were entirely unable to launch a large constellation like Starlink at reasonable cost like Falcon and Starship.
> Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
Not sure whether you are serious. Assuming you are, what would be the better alternative then?
It's not several orders of magnitude smaller. According to ChatGPT, SpaceX has spent $20-30B as of 2023, compared to $160-170B in 2023 dollars. That's less than one order of magnitude, and consider that SpaceX is starting with all the knowledge gained from Apollo, plus 50 years of technological progress.
To your second question, the better alternative is not to send a bunch of junk into space. Aside from low-orbit satellites, space is a waste of time and a distraction, and increasingly appears just to be a way to trick people into ignoring disastrous fiscal and monetary policies while enriching one person.
Don't cite ChatGPT, it's prone to confabulation. According to Wikipedia:
> At its peak, the Apollo program employed 400,000 people and required the support of over 20,000 industrial firms and universities.
That's far more than the roughly 13,000 SpaceX employees. Moreover, that's just Apollo, there were also related programs like Gemini. (The SpaceX employee number also includes people not working on the Starship program.)
> To your second question, the better alternative is not to send a bunch of junk into space. Aside from low-orbit satellites, space is a waste of time and a distraction, and increasingly appears just to be a way to trick people into ignoring disastrous fiscal and monetary policies while enriching one person.
How do you know Musk gets rich from SpaceX? Do you think they make a large profit? Anyway, Starship could be used to launch giant telescopes, which must be useful for science: https://www.palladiummag.com/2024/10/18/its-time-to-build-th...
If you can't see that Musk's entire net worth is downstream of US government action and bubble idiots buying his lies, I can't help you.
Even if thats true, who else can launch satellites at SpaceX price and regularity? This is an actual question, when Falcon 9 stage 2 exploded several months ago, my cubesats got delayed
I know several space startups that's currently limited by launch prices
Who cares? Since the 1960s, space launching has never been limited by supply. It's limited by demand. That's why 80% of SpaceX's cargo is for satellites to support their marginally useful Starlink business. Like Hyperloop, "space startups" are just dressed up snake oil.
Imagine if there were hundreds of "startups" aiming to sink stuff for some reason to the bottom of the Mariana Trench. Sure, doing that is difficult and fun to think about from a science fiction perspective, but the bar to show how such a thing could be useful is and should be quite high.
I asked GPT to give me the 5 most compelling space startups created since 2020. Here's what it gave me:
* Space refueling
* Getting things back from space more cheaply
* Removing space debris
* Getting things to space more cheaply
* Microgravity life sciences
Of these, only the last one is an actual product. The others are just picks and shovels for nonexistent products. And, I don't see why microgravity life sciences requires the ability to deploy unlimited quantities of crap to low-Earth orbit.
Oh my good you have really gone deep into the rabbit hole. Sad to see.
> Since the 1960s, space launching has never been limited by supply.
It has been limited by price. Tons of business that now exists could have existed before. There is a whole history of sat companies that went bust, and big reason they did go bust is because the capital requirements were to high.
And even if your statement was true, the only reason it was even remotely true is because things like the Space Shuttle were subsidized by the government at billions and billions of $ ever year.
Now the government doesn't have to subsidize launch anymore.
> That's why 80% of SpaceX's cargo is for satellites to support their marginally useful Starlink business.
4 million subscribers 'marginally useful' ...
> Like Hyperloop, "space startups" are just dressed up snake oil.
Hyperloop was literally just a idea blue paper. Starlink has 400 million subscribers and has had a literal influence in the larges European war in 7 decades. But sure those are comparable. Totally.
> I asked GPT
That you resort to that because you clearly don't know any of the industry yourself is very telling.
They don’t have 400 million Starlink subscribers you moron.
Correct, its 4 million. I was thinking about 4 million at at 100$ per month initially. 4 million doesn't change my point however.
Please for the love of god don't look at ThunderF00t. He is literally just a guy who made a job out of farming money from uniformed people who dislikes Musk.
He has no credibility at all, like literally 0. Nobody that follows this topics, even if they don't like Musk or SpaceX consider him reputable.
He is literally a professional hater. He just continually moves the goal-posts to always present himself as 'the reasonable skeptic'.
> Currently, around 80% of SpaceX's rockets are dedicated to launching Starlink satellites.
And the other 20% are still more launches then the whole of the Western world would have had before SpaceX.
SpaceX is simply so fucking successful that you have to totally reconsider how you look at the numbers.
> and things like starship don't really have a reason for existing
And if Starship is cheaper, then Falcon 9, and that's literally the whole reason it exists, then making Starlink and other launches cheaper still makes sense. Stopping innovating because of market share is an idiotic thing to do. Its what people argue who don't understand the difference between absolutes and %.
The market for space launch and space economy will be much bigger in 10-30 years. Now we can argue how much bigger, but its defiantly gone be bigger.
And also, Starship literally needs to exists because the government want's to land on the moon. And using Starship and sharing lots of technology with a launch vehicle that is needed for Starlink anyway just makes a whole lot of sense.
> Also, in spite of massive improvements in technology since the 1960s, they're vastly underperforming the track record of the Apollo program.
What an absurd criticism is this? In the 1960 they basically had no regulation, 100% political support and literally unlimited money.
SpaceX had barley any money at all until like 2020 for this project and even then they could only invest a fraction of that into Starship.
If you compare Apollo, the NASA budget was around 20-40 billion $ per year compare to SpaceX who only crossed the 1 billion $ per year in like 2022.
So this is exactly what I mean when I say ThunderF00t has 0 credibiltiy. Nobody should talk arguments like this seriously. Its just arguments from bad faith. I suspect he knows that he is fully of shit, but he has makes a lot of money from continually telling everybody what they want to hear.
> My view is that Tesla, SpaceX, etc. are just cults of personality. Sure, they've produced a non-zero amount of technological progress, but for the most part they're leading us to dead ends.
ThunderF00t is closer to a cult of personality. He has achieved absolutely nothing, he can't even edit videos as well as most 13 year old on tictac. He is a man in his 40 and his humor is even more childish then that of Elon Musk.
And your claim is simply bananas. Calling landing rockets and Starlink 'non-zero' is the understatement of the century. Starship has literally revolutionized space internet and global connectivity, and literally everybody, including all their competitors and every government in the world understands and reconizes that.
And literally some of the largest cooperations on earth, plus major nations are trying to replicate it. Amazon is investing 10+ billion $. Europe, China, Russia all will try to replicate even part of it, but they all know they can't match it.
Lower LEO internet will basically not go away for the rest of human history, unless civilization crashes or somebody comes up with something even better, but we have no idea what that would even be. But somehow you call it a 'dead end'. What are you even talking about.
I mean seriously, please break out of your bubble and look at the world with objective eyes.
Your claims about the dollar amounts the US government has paid to SpaceX are false. The numbers are much higher than that. Just do a quick search.
It’s completely nonobvious to me what value there will be in massively increased amounts of junk being launched into space in the next 10-30 years as you say.
Maybe Starlink is a good idea, maybe not. I don’t really have an opinion on that, and it’s hard for me to picture why and how they have 4 million subscribers.
But even if it is a good idea, what are the next 10 good ideas? And what use is there in sending stuff and people to the moon and mars? It’s all delusional nonsense.
> Your claims about the dollar amounts the US government has paid to SpaceX are false. The numbers are much higher than that. Just do a quick search.
Can you please be exact on what I am wrong about? I didn't even metion a praticular number, the numbers I mention have nothing to do with how much the US pays SpaceX. The numbers I mention was investment in to moon rocket program.
Total amount paid to SpaceX overall is anyway completely irrelevant. Typical Thunderf00t style obfuscation and confusing spreading.
The Apollo program also didn't include how much money was spent on military payloads, so its again, completely irrelevant in the comparison.
And in your typical fashion, you competently ignored the overall point. Appollo had a far, far, far larger budget then SpaceX ever had and it had if for far longer. Arguing with you is utterly frustrating.
> value there will be in massively increased amounts of junk
Ah the old Thunderf00t moving the goalpost move. I guess humans should never have invented ships, because it massive increases the amount of debris in the ocean.
Also please study orbital dynamics. Starlink itself will leave zero orbital debirs.
> Maybe Starlink is a good idea, maybe not. I don’t really have an opinion on that, and it’s hard for me to picture why and how they have 4 million subscribers.
So because you don't understand how the world works, its everybody else that is wrong. Great attitude to have.
> But even if it is a good idea, what are the next 10 good ideas?
Ah we are moving the goal posts again. I really don't want to have a discussion with you, because whatever I say, you will simply move the goal post again anyway.
There are tons of things humanity already does from space. And we can do those things more and better now. That is already good enough. If you personally don't see the value of any of the things humanity has done in space in the last 80 years, then I can't really help you at this point.
In addition there are literally 1000s of space startups we can have an argument about each one of them. Any that I bring up, you can come up with a bunch of reasons why they aren't actually go ideas and you might be right. But at least I'm not arrogant enough to claim to know if they will work or not.
I used the word "junk" not to suggest we're putting too much debris in orbit. It was to say that this stuff is borderline useless. I did some research on starlink, and it looks like most of their users live in the US and just signed up because our country is so dysfunctional it can't offer fiber to people living in places like downtown San Francisco (!). I guess I wish we'd solve the actual problems here instead of engaging in weird space fantasies.
An item the analysis didn't include is using Starlink signals for location, posture, and rotation. I have no idea if they do...
Love the analysis.
Could use more simulation data with NVIDIA Omniverse and thrust vector control
Um, what about using starlink to measure position as option 3!
Starlink as GNSS is definitely a thought that intrigues me and clearly other people too: https://www.technologyreview.com/2022/10/21/1062001/spacex-s...
The tricky parts (that we don't really know as non-SpaceX employees) are:
- how accurate is the clock onboard the satellites? Given that it's likely an OFDM signal the timing is probably pretty good, but given that they're launching zillions of them they probably don't all have atomic clocks onboard
- how accurately is SpaceX tracking their orbits? Kind of a similar answer here... they're doing beamforming to the ground terminals, so it has to be pretty good but we don't really know how good.
- how many SVs are actually visible at a time? We need a minimum of four but the more the better. If there's lots visible we can somewhat work around the first two issues statistically but if there's a limited number than the orbit and clocks need to be super accurate.
Also—how accurately do those satellites track their own position? Unlike the high-orbit GNSS constellations, LEO satellites would bounce around a bit from orbit to orbit, as they're relatively close to the earth and sensitive to uneven distributions of mass. I don't know the exact magnitudes, but I understand they're large by GNSS standards.
Starlink satellites use on-board GPS receivers for extremely accurate (centimeter level) measurements of their position. The orbits which SpaceX reports to the world (for collision avoidance) are based on these measurements.
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