Can SpaceX land a rocket with 1/2 cm accuracy?(theshamblog.com) |
Can SpaceX land a rocket with 1/2 cm accuracy?(theshamblog.com) |
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.
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.
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.
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?
I know several space startups that's currently limited by launch prices
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.
Eg if you space sensors 20m’s apart.
Love the analysis.
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.
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.
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.
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.
> 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.
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.
> 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...
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.
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.
>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.
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.
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.
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.
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.
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.
> 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.
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.
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.
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.
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.
Anybody else thinking this quite the time to be alive?
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
https://nextbigfuture.s3.amazonaws.com/uploads/2023/12/Scree...
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.
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.
/raptor 3 pumps look like you could hold them in your hands but iirc they deliver over 100k horsepower each.
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.
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.
[0] https://en.wikipedia.org/wiki/Real-time_kinematic_positionin...
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.)
Good article. It is nice how it goes through all the points systematically.
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 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.
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 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.
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.
There are so many other methods that the lander can use to know where the tower is.
> 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.
> 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.
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?
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.
Impossible apparently.
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."
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.
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 always stuck out in an otherwise excellent bit, because you should definitely _not_ be taking the absolute value of your control error.
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.
[1]: https://www.youtube.com/watch?v=pAPt5vbr-YU (don't recall timestamp, sorry)
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...
Or in fact, you need even better than that, since you don't want your whole error budget used up by the GNSS system.
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.
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."
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.
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.
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.
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.
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.
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.
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.
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.
There have been many airplane crashes because of sudden unexpected wind changes while landing.
It's definitely floated around for a while, but it grew in popularity in the past few years.
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.
This is the part I question though. Seems like an org as well motivated as SpaceX could easily solve that if it was necessary.
But in realtime? (single-digit second latency, at least)
