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https://twitter.com/elonmusk/status/1336808486022258688 https://twitter.com/elonmusk/status/1336808486022258688 Successful ascent, switchover to header tanks &
by guardiangod 6y ago
https://twitter.com/elonmusk/status/1336808486022258688 https://twitter.com/elonmusk/status/1336808486022258688
Successful ascent, switchover to header tanks & precise flap control to landing point!
Fuel header tank pressure was low during landing burn, causing touchdown velocity to be high & RUD, but we got all the data we needed! Congrats SpaceX team hell yeah!!
It seems that the Raptor engines didn't failed due to defects at the end of the landing. The fuel pressure from the header tank wasn't high enough and the engines became fuel starved. It is obvious in the video as the engine exhaust became bright green at the end, a sign that the engine was restarting by TEB.
Edit:
https://twitter.com/elonmusk/status/1336810077555019779 https://twitter.com/elonmusk/status/1336810077555019779
Mars, here we come!!
Indeed
- nikolay 6y agoA nice try to make an explosion sound like a success - reminds me of the Soviet times when the Party was never wrong!
- jessriedel 6y agoIt's a test flight. Musk gave only a 1/3 chance of mission success before the flight.
- nikolay 6y agoYes, but a 1/3 success chance doesn't not mean a 2/3 one of an explosion.
- robotresearcher 6y agoAfter engine ignition, isn't it pretty much that success or massive explosion are the only outcomes?
- NikolaeVarius 6y agoNah engines are able to turn off after ignition. Thats what the Raptor safety is. Usually the blow or moment is when it lifts off the tower with one notable exception that I know of. https://en.wikipedia.org/wiki/Mercury-Redstone_1 https://en.wikipedia.org/wiki/Mercury-Redstone_1 Technically the Shuttle go or blow moment is when the SRBs are turned on. But yes, otherwise in the spirit, it will either blow up or be generally sucessful.
- aardvarkr 6y agoSo you’re saying that if the engines had been off the starship wouldn’t have exploded? Try again bud. That’s still an object full of compressed methane and liquid oxygen falling at terminal velocity.
- NikolaeVarius 6y agoThis is such a straw man that I don't even know where to begin to answer.
- valuearb 6y agoSo you are admitting that what Musk meant was they had a 2/3s chance of an explosion.
- pertymcpert 6y agoWas it a complete failure?
- nikolay 6y agoWell, nothing is a complete failure ever from your point then - you always learn from mistakes.
- sirk390 6y agoYes, but if it explodes during launch you learn only a little(you don't have any data for flight and landing) Here it went almost perfect because they have the data for everything to be able to fix issues
- mlyle 6y agoWe have launch, controlled flight through the desired test regime, and a botched landing. And as others have said, it's either complete success-or-explosion that's expected in this area.
- deleted 6y ago[deleted]
- pertymcpert 6y agoWhat point was that? I just asked you a question.
- ChrisFoster 6y agoNo, I'd say it was an almost-complete success. The point of this was to test several things which they've never tested before and gather data to drive design improvements. They successfully tested: ascent under three engines, flap-controlled aerodynamic descent to the landing site, the landing flip maneuver - including drawing propellant from the header tanks - and final landing burn. They didn't stick the landing, but it looks like they got test data from all the planned test activities. The explosion will prevent gathering some data from post-flight inspection, but other than that I doubt it has much affect on future development. To look back on SN5/SN6 testing, they stuck the landings with those prototypes, but the prototypes themselves are now obsoleted by the new prototypes in production (up to SN16?!)
- elihu 6y agoThey had to get a lot of things right on the first try for a successful landing. They got a lot of them right, but had trouble with fuel pressure at the end and landed too hard because there wasn't enough thrust. As problems go, that's a relatively simple one that they ought to be able to address. The ascent appears to have been successful (though for a few moments it looked like something caught on fire and I'm not sure if that was planned or expected). The glide worked. The rocket was able to navigate to the landing pad. Next time they'll be working with a lot more information. This seems like overall it was a success, even though they're down one rocket and three engines. A failure would have been the rocket blowing up on the pad during launch or other similar mishap from which they wouldn't have learned much aside from "make sure that doesn't happen again".
- fastball 6y agoThe fire after first engine cutoff was just extra gases from the cutoff engine getting trapped and burning off.
- jryle70 6y agoSince you're are such impressively unimpressed, maybe you could tell us what the objectives of this test were and how SpaceX failed to achieve them?
- nikolay 6y agoNo, I'm commenting on Elon Musk's comment. I would have taken a humble: "Sorry, we blew up this (literally), but we're gonna get better after learning from our mistake." You blow things up, you fail. No excuses, sorry! Don't start a test knowing it most certainly will fail! Start a test when you're a lot more confident!
- sitharus 6y agoBut it didn’t fail, landing wasn’t a test objective.
- restalis 6y agoLanding may not have been one of the primary objectives, but it clearly was an objective, since they didn't just let it crash at will after having completed the flight maneuvers.
- DarmokJalad1701 6y ago> Don't start a test knowing it most certainly will fail! Start a test when you're a lot more confident! Good thing you aren't the one designing these things.
- mkl 6y agoThe purpose of a test is to gather the data you need to improve. Scientists and engineers constantly start tests knowing it will most likely "fail". Actual failure would be a test that didn't produce any data.
- nikolay 6y agoNo, an explosion and destruction of equipment is a failure. Why do you keep dancing around this truth? It is a failure everywhere else in the world! You should've listened to the commentary of foreign anchors! They don't look at it as a success!
- restalis 6y agoYou're right that the destruction of equipment and loss of material resources in general is a failure that could have been prevented with a more cautious approach, but that's not the entire picture. Another resource, one that Mr. Musk cares more about, is time. He both affords to and is willing to throw material resources at the technology development problem, even at a loss (i.e. the stated "1/3 chance of success"), just so he could "move fast and break things" (from time to time, if it comes to that). In this context, even with that prodigious blow at the end, having at least some of the testing goals met can be a genuine success in Musk's own eyes, not just a sell for the rest of us. The political actors, on the other hand, had to play the perception image game because that's the world they reside in. The politicians' primary objective in that space program has always been the prestige that comes attached from bearing it to fruits. Sure, in a race they went on in a similar fashion and threw copious amounts of material resources, but for them the cost of technical failures were not so much about loosing material as were about loosing face, hence the propaganda that had to handle/mitigate that. Same rocket science development game, different rules for the actors involved.
- jonplackett 6y agoJust amazing to watch. The flip down to gliding just looked so bizarre and futuristic. It's the big WTF I got from first seeing Grasshopper stop and hover in mid air and land again. That's not what rockets are meant to do! Except of course they are meant to do it!
- jvzr 6y agoI've been following SpaceX for years, and this is exactly my reaction today! Watching the belly flop and the (relatively) slow descent, it felt completely alien, surreal. I'm in utter awe. Congrats to the teams involved, can't wait for SN9 and the rest of Starship!
- fnord77 6y agothe apollo lunar lander did pretty much the same thing.
- galacticaactual 6y agoThe Apollo lunar lander objectively did not belly flop through atmosphere at 1G while having to deal with aerodynamic control surfaces.
- NikolaeVarius 6y agoAre you seriously comparing the Lunar Lander to this? The Lunar Lander was piloted since the computers couldn't do everything, but at the same time a human was good enough at piloting to be able to take over for what the computer couldn't do. This is the result of modern day CFD that that would take humans millions of years to do by hand
- serf 6y ago>This is the result of modern day CFD that that would take humans millions of years to do by hand the package as a whole, yes. belly reorientation for flight has been a thing since the early American arms' race. It's a useful missile trait. Gimbaled vector rockets have existed since the 1940s.[0] Yes, restart is very important -- it's not a requirement for atmospheric belly flight, though. [0]: https://en.wikipedia.org/wiki/RTV-A-2_Hiroc https://en.wikipedia.org/wiki/RTV-A-2_Hiroc
- augusto-moura 6y agoRUD = Rapid Unscheduled Disassemble For the people not familiarized
- diimdeep 6y ago> With liquid propellants (but not gaseous), failure to ignite within milliseconds usually causes too much liquid propellant to be inside the chamber, and if/when ignition occurs the amount of hot gas created can exceed the maximum design pressure of the chamber, causing a catastrophic failure of the pressure vessel. This is sometimes called a hard start or a rapid unscheduled disassembly (RUD). https://en.wikipedia.org/wiki/Rocket_engine#Ignition https://en.wikipedia.org/wiki/Rocket_engine#Ignition
- NikolaeVarius 6y agoRaptor doesnt use TEB. It uses spark ignition
- guardiangod 6y agoIt must be the engine burning its internal alloys then. Probably the turbopumps' due to the fuel running rich?
- NikolaeVarius 6y agoProbably oxygen, since the fuel tank had low pressure
- guardiangod 6y agoThat's my suspicion as well. If it's methane rich then the exhaust would have a lot of soot due to incomplete combustion. If it's oxygen rich then the burn temperature would be much higher than designed, and every internal metal surface would get oxidize in a hurry.
- xcskier56 6y agoThis line of thought is very reasonable for normal engines, but I wonder if it’s not quite right for the raptor. I’m not 100% on this, but I think the raptor actually runs really oxygen rich. According to Elon’s tweet and Wikipedia, it runs 3.5-1 O2-CH4. It runs so lean that the unburnt o2 cools things. If it were running closer to 1-1 (low ch4) then it would run much hotter and burn things like we saw. Edit: reading more I’m not positive they run O2 rich anymore
- kortex 6y agoMinor correction: 4.0 lox/methane is stoichiometric. 3.8 is rich. 3.55 is very rich. It runs fuel rich to keep cool and possibly increase specific impulse.
- 6y ago
- sitharus 6y ago> It is obvious in the video as the engine exhaust became bright green at the end, a sign that the engine was restarting by TEB. They wouldn't carry enough TEA/TEB to make that much flame - it's likely the engine itself burning. Also I don't think Raptor uses TEA/TEB as that would put a cap on the number of restarts - not something you want for an interplanetary mission!
- potiuper 6y agoThis test of lossless convexification showed good results with the stochastic control problem, but the fluid dynamics model could use some work before: > Mars, here we come!!
- mlindner 6y agohttps://www.youtube.com/watch?v=RXJKdh1KZ0w https://www.youtube.com/watch?v=RXJKdh1KZ0w
- pbreit 6y agoWere all the engine outages planned?
- TrueDuality 6y agoI believe some were. The plan was to switch over to two engines on ascent, and use two engines during the rapid deceleration. The full shut down was intentional. It looks like they might have briefly went to one engine during ascent but it wasn't entirely clear. The flame out of the first shut off was probably not intentional as well. It's really hard to tell. None of that information was official though so take it with a grain of salt, it's all come from personal knowledge and analysis by some people watching.
- deleted 6y ago[deleted]
- dpifke 6y agoAccording to Musk, yes: https://twitter.com/elonmusk/status/1336818987389181952 https://twitter.com/elonmusk/status/1336818987389181952 The orientation change just prior to shutoff is also a clue: https://twitter.com/joebarnard/status/1336820348071849986 https://twitter.com/joebarnard/status/1336820348071849986
- TigeriusKirk 6y agoWhat would cause the fuel pressure to be too low?
- LeSaucy 6y agoCentrifugal forces of doing the belly flop maneuver. Ever try to flip a spinning object sepaofrom the axis it’s spinning on? Imagine a fuel pump or turbine full of liquid oxygen. The engineering to get this to work is astounding.
- aardvarkr 6y agoCan you explain this more? I’m intrigued to learn about it
- deleted 6y ago[deleted]
- bigyikes 6y agoNot sure, but they might be talking about this: fill a bucket with water and swing it upside down over your head. The water stays in the bucket because centrifugal forces apparently push the water outwards. The same may have happened for the fuel, I guess lowering the pressure? I know nothing about rockets.
- sq_ 6y agoAside from what a sibling comment mentioned about fuel sloshing from the flip maneuver, Raptor/Starship use autogenous pressurization (i.e. some of the gas produced by the engines is tapped off to pressurize the tanks), so there could have been an issue with that, too.
- nickik 6y ago> It is obvious in the video as the engine exhaust became bright green at the end, a sign that the engine was restarting by TEB. The Raptor doesn't use TEB. It uses spark ignition. The green is most likely 'engine rich' exhaust. Meaning the cooper cladding of the engine bell started to burn away.
- strangemonad 6y agoRaptors don’t use teb or hypergols. This is some other fuel mix reaction
- ChuckMcM 6y agoWow, thanks for that link, clarifies what happened. I never thought I'd see a "flash gordon" shaped space ship actually fly, and no here we are.
- Gravityloss 6y agoI think once the aerodynamics are tried a little bit more, it can be refined to a lifting body. Strakes and deltaish wing, something a bit like the space shuttle or X-37. Having completely cylindrical body and two sets wings now for the prototype phase makes control authority good and iterating changes very easy (you can change either wing shape easily), even if it's not optimal mass wise.
- CodeGlitch 6y ago"Fail fast, fail often" Seems to be working for SpaceX. Makes for impressive videos too. Congratulations to all involved.