20 ms·
Can SpaceX land a rocket with 1/2 cm accuracy?
- sebzim4500 2y agoThe 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.
- magicalhippo 2y agoWhen 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 https://www.youtube.com/watch?v=pAPt5vbr-YU (don't recall timestamp, sorry)
- beerandt 2y agoRtk 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.
- scottshambaugh 2y agoI'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.
- londons_explore 2y agoIf 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.
- michaelt 2y agoIn 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/S0263224118300873 https://www.sciencedirect.com/science/article/abs/pii/S02632...
- stavros 2y agoWhat's absolute position? Isn't all position relative?
- westmeal 2y agohttps://www.youtube.com/watch?v=bZe5J8SVCYQ https://www.youtube.com/watch?v=bZe5J8SVCYQ
- adastra22 2y agoAbsolute position is global lat/long coordinates. Relative position is “I’m 0.5cm from the middle of the peg.”
- willglynn 2y agoGlobal 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.
- adastra22 2y agoThere 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.
- bmicraft 2y agoMy 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.
- snypher 2y agoI'd love to hear about 2cm accuracy uncorrected. Does it have dual GPS units?
- bmicraft 2y agoWell, 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.
- cubefox 2y agoIt'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.
- tocs3 2y agoI 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.
- mbell 2y agoArmchair 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.
- echoangle 2y agoNot 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.
- candiddevmike 2y agoDoes SpaceX even use traditional GPS? I'd assume with something like Starlink they would be able to employ something more precise/fit for purpose.
- andrewmcwatters 2y agoGNSS 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.
- ortusdux 2y agoI wonder if they will paint pin alignment marks on the grabber arms?
- chasd00 2y agoIf 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.
- lostdog 2y agoYou 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.
- aeyes 2y agoIs this really viable given all the electromagnetic interference the rocket motor exhaust plumes are generating?
- AlgorithmicTime 2y ago[dead]
- generuso 2y agoFalcon-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.)
- gibsonf1 2y agoUm, what about using starlink to measure position as option 3!
- tonyarkles 2y agoStarlink as GNSS is definitely a thought that intrigues me and clearly other people too: https://www.technologyreview.com/2022/10/21/1062001/spacex-starlink-signals-reverse-engineered-gps/ 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.
- perihelions 2y agoAlso—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.
- generuso 2y agoStarlink 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.
- mclau156 2y agoCould use more simulation data with NVIDIA Omniverse and thrust vector control
- varispeed 2y agoAnd 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.
- fxtentacle 2y agoMost hackerspaces have a laser cutter strong enough for a few mm of steel sheet. So chances are, you could make it yourself.
- Spunkie 2y agoI 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.
- mclau156 2y agoA lot of people think it landed on the large grid fins, this is not true it actually landed on much smaller landing pegs
- nordsieck 2y agoThis 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 https://www.youtube.com/watch?v=ExV6PHRM8eI
- stronglikedan 2y agoI was impressed before. Now I'm doubly impressed after having watched that. Thanks.
- mdrzn 2y agoThis is even more mindblowing than landing on the fins. Amazing.
- Culonavirus 2y agoLanding 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_fin_damage_during_hot_staging/ https://www.reddit.com/r/SpaceXLounge/comments/1g3bi7s/grid_...
- krisoft 2y ago> 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.)
- meindnoch 2y agoThe 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.
- mucle6 2y agoReference: https://www.youtube.com/watch?v=bZe5J8SVCYQ https://www.youtube.com/watch?v=bZe5J8SVCYQ
- killjoywashere 2y agoThis 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?
- rcxdude 2y agoIt'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.
- kabdib 2y agoI wonder how much of a problem crosswinds are. Not a lot of mass, and that big can has a lot of sail area.
- weard_beard 2y agoFrom 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."
- therealfiona 2y agoMaybe 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.
- deleted 2y ago[deleted]
- blackoil 2y agoRocket alone need not be this accurate as grabber arms should also do some maneuvering to get the final accuracy.
- LooseMarmoset 2y agoYou 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.
- slashdave 2y ago0.5cm 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.
- varjag 2y agoYup it's surface amplitude with the engines running is probably more than that.
- chasd00 2y agois "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.
- slashdave 2y agoThe larger size makes control much easier.
- cryptonector 2y agoIt'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".
- slashdave 2y agoThat's worse, considering that the control points are a huge distance away. Just flex alone has to be huge.
- 2y ago
- burningChrome 2y agoJust 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?
- stagger87 2y agoWell, 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.
- golemotron 2y agoThe fact that someone tried is significant. We've had 50+ years of not trying.
- jerf 2y agoAs 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.
- ars 2y agoI 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.
- lysace 2y agoYes, 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.
- generuso 2y agoAs 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.
- cubefox 2y agoThere is also an interesting analysis about the control engineering perspective: https://youtube.com/watch?v=QHikx6kVvAo 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.
- generuso 2y agoIt 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/eda2b96bddf945629be2c9d2e3bc87231d 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.
- cubefox 2y agoIt'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) https://en.wikipedia.org/wiki/Sky_crane_(landing_system)
- mensetmanusman 2y agoThe designers of the raptor engine should get a Nobel prize in chemistry for combustion physics.
- paulsutter 2y agoThe 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 https://www.youtube.com/watch?v=vYA0f6R5KAI title: "GPUs To Mars: Full Scale Simulation of SpaceX's Mars Rocket Engine"
- thot_experiment 2y agoThis talk is FANTASTIC and has been an inspiration for me for years as well. Highly HIGHLY recommend it.
- paulsutter 2y agoThe 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.
- cryptonector 2y ago> 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.
- HarHarVeryFunny 2y agoThe 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.
- cryptonector 2y agoRight, 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.
- thot_experiment 2y agoMost 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.
- cubefox 2y agoBill 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.
- asadotzler 2y agoThe buoys were not trivial devices. See https://x.com/CosmicalChief/status/1626333723514834944 https://x.com/CosmicalChief/status/1626333723514834944
- mikewarot 2y agoIf 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?
- pedrocr 2y agoThis 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.
- rkagerer 2y agoI found this video from the perspective of a landing pin interesting, especially when played back at low speed: https://youtu.be/ExV6PHRM8eI?t=17 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 https://youtu.be/JlcrNakUGVs?t=3
- HarHarVeryFunny 2y agoWorth 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/Screen-Shot-2023-12-17-at-8.47.50-AM-768x505.jpg https://nextbigfuture.s3.amazonaws.com/uploads/2023/12/Scree...
- nurettin 2y agoNot 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.
- sfblah 2y agoTake 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.
- cubefox 2y ago> 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?
- sfblah 2y agoIt'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.
- thamer 2y ago> 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 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 https://www.sparkfun.com/products/16481.
- simgt 2y agoI 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_positioning https://en.wikipedia.org/wiki/Real-time_kinematic_positionin...
- simgt 2y agoI 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.
- coconoconut 2y ago[flagged]
- louwhopley 2y agoGiven 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.
- scottshambaugh 2y agoIt’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.
- justinclift 2y ago> 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.
- Zeetah 2y agoAn 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.