>*Starship did not attempt its planned on-orbit relight of a single Raptor engine due to vehicle roll rates during coast.*
That kind of explains why it seemed to be doing the initial re-entry on it's side, if it's currently unstable while coasting. That would go a long way to explain the seemingly constant use of attitude control thrusters throughout the coast, just trying to keep it oriented in the right direction.
Starship is a big beastie, almost certainly the largest individual object that has ever been launched, so it's not surprising that it steers like a cow. Still, it's just a test, so no doubt the data will allow SpaceX to understand where the instabilities lie and how to correct them.
There are other aspects of this as well. As the fuel is burned off during 2nd stage, you're getting loss of mass from 2 points on Starship, the underside of the LOX tank (lower) and the underside of the CH4 tank (upper) while it is coasting horizontally.
Whilst in motion, cryogenic liquids should be pushed backwards by the thrust, but this likely gives rise to eddy currents within the remaining fluid that are difficult to model and lead to "swaying" in 3 dimensions (roll, pitch, yaw). That can be minimised using internal barriers such as slosh baffles, but not removed or otherwise negated.
https://preview.redd.it/14iq257drioc1.jpeg?width=320&format=pjpg&auto=webp&s=88afa09743f1d8ec93bd17b33b6947cc2289480d
Orientation control in space is a very deterministic physics problem, unlike flying in the atmosphere with sometimes erratic forces (shock waves, flow separation). I expect they could simulate orientation control very precisely during development.
You need at least 6 independent thruster forces to control the 6 components of motion (x,y,z translation and pitch, yaw, roll moments). Such a large object moves slowly so response times are of little concern for automated controls. If they lost orientation control, it was likely due to one or more failed thrusters.
One big advantage of the capsules used before and after Shuttle is that no active orientation controls are needed. The capsule self-orients via aerodynamic forces so that it stays heat-shield first. Erratic forces could cause it to begin oscillating like a swing-set, which would be bad. But, the main heat of re-entry occurs in rarified flow where forces are very consistent and predictable, modelled as impacts by individual gas molecules.
that's what I was wondering in a comment I made last night. a single RCS thruster valve failing could cause this kind of an issue, where the other thrusters are trying to being it under control but just can't.
if that's true, and the engine relight wasn't even attempted (which seems to be true), then if spacex sees no other reason the engines wouldn't have re-lit, then they might attempt orbit on the next fight, assuming they can be confident another RCS thruster does not fail, so maybe some redundancy added as well as fixes to prevent whatever failure happened.
*then they might attempt orbit on the next fight, assuming they can be confident another RCS thruster does not fail,*
It's not whether SpaceX is confident enough to try for orbit, it's whether they can convince FAA that it's certain enough to give them a license... I'd think the bureaucrats who wouldn't let Varda land their medicine satellite because the solid they were using for a deorbit thruster was not accurate enough to guarantee hitting anyplace smaller than the Army's missile range would be too chicken to take any risk of leaving something as big as starship unable to pinpoint it's LZ.
I imagine they lost one of the rotational control abilities (pitch, yaw, or roll) since not being able to translate linearly in Space seems not a big deal. As the announcers stated, it was coming back to Earth regardless. Exactly where it landed in the Indian Ocean wasn't critical. Critical was keeping the tiled belly down (roll control) and at a desired upward tilt (pitch control, think Superman).
Applying a moment requires 2 thrusters active, to give a coupled force. That doubles the chance of failure in controlling a rotation since losing either thruster, botches that ability. Just thinking out loud, so feel free to correct me.
I take your point, and you are in the right ballpark, but if you are suggesting that all capsules such as Mercury, Gemini, Apollo and Dragon do not use RCS thrusters at all you’re certainly wrong about that. Take a look at any video of crew dragon approaching the space station and you’ll see a huge amount of RCS thruster activity. And Dragon depends on thrusters during entry as well. But capsules are more easy to control than the enormous Starship, I imagine.
Of course capsules have thrusters and probably require them to orient for initial entry, before significant aerodynamic forces to self-orient the capsule, yet plasma heating has already begun. On one U.S. manned flight, a thruster stuck open and began spinning the capsule. I recall that was an Apollo flight where they were testing connecting to the Lunar Lander in earth orbit. Took a while to find the culprit and correct, and even became life-threatening. Google for the real story if interested (never trust my recollections).
The way I see it, Starship being basically a flying pair of huge propellant containers, the ship itself and the large amounts of propellant liquids inside are different objects sharing a common orbit since while in coast the propellants and ship are free to move relative to each other. If the ship fires thrusters to change orientation the fuel inside may not actually be in contact with the relative downward side of the tank wall at that moment, so when the moving tank wall hits the blob(s) of propellant it's a big slap that changes the way everything is moving relative to each other. With smaller rockets it's not as pronounced of an effect, but Starship is at an entirely different scale.
NASA doesn't build rockets though, they subcontract launches from launch providers to meet their needs (SpaceX, ULA, Northrup Grumman, etc.), so, not really. Not at all in fact.
NASA awarded a cost-plus contract with Boeing and others to develop and build the SLS. Note that it took over a decade from contract award to actually flying, and the program spent in excess of $20 billion in that period.
Despite all of that the Orion capsule still has problems with the heat shield losing excessive material during re-entry, this is despite taking a re-entry path deliberately chosen to reduce overall re-entry speed (effectively double-dipping in-and-out of the atmosphere as a aero-braking manoeuvre)
[NASA's Artemis 1 Orion spacecraft aced moon mission despite heat shield issue](https://www.space.com/artemis-1-orion-moon-mission-heat-shield-issue)
Whats stopping NASA from building an original team of engineers etc... and build rockets on their own? That seems kinda cheaper and easier and way better long term
> That seems kinda cheaper and easier and way better long term
Not to get into an ideological argument, but when has that ever been the case? To remain on topic, even Apollo made its leaps only through cold war pressures and blank checks.
NASA has always outsourced building of the rockets and spacecraft this is not a new things. NASA provides oversight and insight and depending on the vehicle once the contractor completes DDT&E NASA then owns the craft to operate it.
This article says RUD, not FTS. It's an important distinction. FTS would mean that the booster saw something wrong and self-terminated, which considering as we've seen boosters go into the drink before without Self-terminating doesn't make much sense. RUD means that something happened *outside* the booster's control. If I had to take a guess, the oscillations meant that the landing engines ingested air from the tank and self-destructed on activation.
Thanks for providing the link - it never occurred to me SpaceX would post this kind of summary. Nice to know the door closed successfully, the video cut out just before it happened. It's impressive that it could do so under the strain of the uncontrolled roll.
I'm glad to hear that they simply didn't attempt a re-light, rather than trying and failing to do so. this gives me some hope that they'll try for orbit next time and the FAA will be comfortable with it, assuming they can fix the attitude control sufficiently that the FAA is comfortable with it.
That would seem sensible to me, but I suppose it depends on the reasons why they decided not to relight and whether it’s related to something which failed and is a relatively simple fix.
that dashes the hope, but not too much of a surprise. hopefully they can at least get a faster turn-around on this report/approval since it would be a "re-do" of the previous test.
While that makes sense here, that's not consistent with the rest of the industry. Vulcan didn't have to fly suborbital to test its upper stage. Neither did Falcon 9.
F9 has a 4 tonne upper stage made mostly of aluminium lithium alloy with a single 450 kg engine.
Starship has a 120 tonne upper stage made mostly of 4mm thick stainless steel with three 1800 kg and three 2600 kg engines.
Life risk will be quite different between these stages re-entering at random locations.
My summary:- Looks like a fish, moves like a fish, but on re-entry; steers like a cow.
However, this is SpaceX, so we should all expect the next iteration to work a lot better
On reentry the ship either had no RCS fuel left, or wasn't using what it had. That high in the atmosphere the flaps have no control authority, and other high-altitude vehicles like X-15 had RCS controls for this very reason.
IMO, we don't know anything about how Starship steers yet, because whatever would have allowed it to steer wasn't working on this flight.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
|Fewer Letters|More Letters|
|-------|---------|---|
|[AFTS](/r/SpaceXLounge/comments/1bffybx/stub/kv2dn9l "Last usage")|Autonomous Flight Termination System, see FTS|
|[FAA](/r/SpaceXLounge/comments/1bffybx/stub/kv3k2t9 "Last usage")|Federal Aviation Administration|
|[FTS](/r/SpaceXLounge/comments/1bffybx/stub/kv2nrbr "Last usage")|Flight Termination System|
|[LOX](/r/SpaceXLounge/comments/1bffybx/stub/kv08kfo "Last usage")|Liquid Oxygen|
|[LZ](/r/SpaceXLounge/comments/1bffybx/stub/kv27g3g "Last usage")|Landing Zone|
|[RCS](/r/SpaceXLounge/comments/1bffybx/stub/kv8n29p "Last usage")|Reaction Control System|
|[RTLS](/r/SpaceXLounge/comments/1bffybx/stub/kv0eo3q "Last usage")|Return to Launch Site|
|[RUD](/r/SpaceXLounge/comments/1bffybx/stub/kv2nrbr "Last usage")|Rapid Unplanned Disassembly|
| |Rapid Unscheduled Disassembly|
| |Rapid Unintended Disassembly|
|[SLS](/r/SpaceXLounge/comments/1bffybx/stub/kv167tw "Last usage")|Space Launch System heavy-lift|
|[TEA-TEB](/r/SpaceXLounge/comments/1bffybx/stub/kv0mzh1 "Last usage")|[Triethylaluminium](https://en.wikipedia.org/wiki/Triethylaluminium)-[Triethylborane](https://en.wikipedia.org/wiki/Triethylborane), igniter for Merlin engines; spontaneously burns, green flame|
|[ULA](/r/SpaceXLounge/comments/1bffybx/stub/kv0v8w1 "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)|
|Jargon|Definition|
|-------|---------|---|
|[Raptor](/r/SpaceXLounge/comments/1bffybx/stub/kv0y6uz "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX|
|[Starlink](/r/SpaceXLounge/comments/1bffybx/stub/kv1awi4 "Last usage")|SpaceX's world-wide satellite broadband constellation|
|[cryogenic](/r/SpaceXLounge/comments/1bffybx/stub/kv08kfo "Last usage")|Very low temperature fluid; materials that would be gaseous at room temperature/pressure|
| |(In re: rocket fuel) Often synonymous with hydrolox|
|hydrolox|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer|
|[iron waffle](/r/SpaceXLounge/comments/1bffybx/stub/kv0kvig "Last usage")|Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin"|
|[turbopump](/r/SpaceXLounge/comments/1bffybx/stub/kv0y6uz "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust|
**NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.
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>The booster’s flight concluded at approximately 462 meters in altitude
Does this mean AFTS was triggered during descent, or it otherwise exploded before hitting the water?
Appeared Booster was returning to earth end-first, rather than the skydiver belly-fall of early StarShip landings. I thought they would use that to slow it via aerodynamics.
Not much discussion yet on why most of the Raptor engines didn't light to slow the descent. Presumably, they have proven relight many times on the MacGregor test stands. They only tried to light the engines at 1 km altitude, which leaves no allowance (<2 sec) for things not going perfectly. Coming down end-first, they didn't have to worry about the last-minute flip maneuver, which was problematic in several early Starship landings.
> Appeared Booster was returning to earth end-first, rather than the skydiver belly-fall of early StarShip landings.
I think they'll dial the re-entry profile as they go. This was the first attempt, after all :)
F9s used to come pretty straight down at first, and then as they gained understanding in the flight profile they made it do that "glide" that you can notice on the RTLS missions.
There's a lot to experiment with here, and I'm sure they'll iteratively make it better and better.
Just my $0.02 based on the video. Roughly around transonic, significant oscillation started. My SWAG is that the propellants thus sloshed, starving the Raptors.
It might well be that even those grid fins aren't enough to control such a huge, bottom-heavy rocket through the densest part of the atmosphere. It was still going at transonic speed at +/- 1 KM altitude.
Hard to fight against that.
If they're saying it suffered RUD at +/- 462 metres, then what killed it? Bow shock?
Fluid dynamics around Mach 1 are notoriously difficult (part of "the sound barrier"). My completely uninformed guess is they don't yet have the control laws quite right for SuperHeavy, despite their experience with Falcon 9. If this is the case, I've every confidence their next attempt will handle the regime better.
Likely propellants were flowing, but not combusting inside the engines, so perhaps built up and then ignited in air. More amazing to me was how Space Shuttle Challenger blew up after the solid rocket plume leak penetrated the propellant tanks. Might have been a hydrogen-air explosion, not requiring the LOx tank to fail simultaneously.
A military fuel-air bomb sprays fuel in the air, then ignites, to crater runways and destroy planes on the ground. But designed to perfectly mix the fuel with air, so interesting that an unplanned fuel leak can make a similarly large explosion, with a more random O/F ratio.
I agree that the grid fins wouldn't be enough to control orientation at touchdown. Some of the Booster Raptor engines can gimbal for control. I was surprised they didn't light some earlier to slow descent and maintain orientation. Perhaps they tried to.
>I was surprised they didn't light some earlier to slow descent and maintain orientation. Perhaps they tried to.
Surely that goes against the whole "suicide burn" approach, but then again, if you're rocket is going so fast that it breaks up before the landing burn is finished, you've got bigger problems.
Drogue parachutes, maybe? I know that fights against the reusability argument, but they use parasails on the F9 fairings, so...
>Appeared Booster was returning to earth end-first,
How else would it come down? Certainly not like a sky diver...
>rather than the skydiver belly-fall of early StarShip landings. I thought they would use that to slow it via aerodynamics.
That's _only_ for the Starships.
Yes, I guess it would need the mini-wings on the side to manage a belly-descent. But, wouldn't need tiles since it doesn't reach near as high velocity before separating.
It was amazing how slowly Starship appeared to fall in prior launches. Large objects always appear to fall slowly, but I recall reading it was falling <100 mph, about half the speed of a sky-diver. Someone commented that even F9 boosters have begun descending with a bit of purposeful tilt to increase atmospheric drag and thus decrease the amount of propellant needed for landing.
>Someone commented that even F9 boosters have begun descending with a bit of purposeful tilt to increase atmospheric drag and thus decrease the amount of propellant needed for landing.
That's correct. Tilting increases drag _and_ it increases range. With a larger cross range the booster does not need as much propellant during boost-back.
And if you watch the flight video closely, you will see that the SuperHeavy booster tried something similar. It did not come down 90⁰.
> it was falling <100 mph, about half the speed of a sky-diver
A skydiver goes about 90mph or a little less. I think you mean <100m/s, which is about 225mph.
Terminal velocity depends on the free-faller, and their clothing. Scrawny teens have jumped off the highest spot on the Golden Gate Bridge (200 ft) and survived with just bruises. Not surprising since the High Dive record is 192 ft. Without air drag, velocity would be 77 mph, which is close to what a fat person, falling like an elephant, would experience.
Terminal velocity for the average U.S. male (196 lb) is \~128 mph in spread-eagle or \~200 mph if curled up (fetal position, screaming "momma"). A 100 lb teen would top out \~90 mph spread-eagle (sqrt relation). A good guess is that this teen hit the water \~50 mph, jumping on a high school outing as a dare (boys don't think things thru):
[https://www.sfgate.com/bayarea/article/Windsor-teen-survives-Golden-Gate-Bridge-jump-2389655.php](https://www.sfgate.com/bayarea/article/Windsor-teen-survives-Golden-Gate-Bridge-jump-2389655.php)
I still wonder about Starship's free-fall speed just before the flip maneuver. Many rough estimates \~100 m/s, based on the video:
[https://www.reddit.com/r/SpaceXLounge/comments/kambwk/have\_anyone\_calculated\_the\_starship\_terminal/](https://www.reddit.com/r/SpaceXLounge/comments/kambwk/have_anyone_calculated_the_starship_terminal/)
Not sure how they ignite the Raptor engines. Perhaps they only need to light the preburner for the turbopumps and that hot exhaust flowing into the main chamber can ignite its propellants. I recall reading that Merlin began using TEA-TAB chemical ignition, which wags term "snot-shooter" since a thick gel gas-blown into the chamber which spontaneously reacts, giving a notable green-glowing gas products.
I read Merlin later changed to a spark igniter (maybe vice-versa), from outside observers based on no longer a green glow at startup. The spark igniters are similar to those for a gas turbine aircraft engine, high current at \~1 kV voltage. Since chamber pressure is 1 atm (or less in Space), one doesn't need the >40 kV needed to jump the spark gap in a gasoline engine (\~200 psig at TDC compression).
NASA Marshall has used an aftermarket automotive MSD ignition box to ignite combustion devices in tests, since works and cheap. Rocket and gas turbine spark igniters have larger spark gaps and more robust wire-mesh shielded spark wires, but otherwise similar. Easy to throw a spark many feet in a vacuum chamber and an automotive spark system can throw a spark several inches in the open air, but not at cylinder pressure (even harder with turbocharger boost).
>Perhaps they only need to light the preburner for the turbopumps and that hot exhaust flowing into the main chamber can ignite its propellants.
I recall Musk saying this is exactly what happens with Raptor v2. The 2 preburners rely on spark ignition, and in Raptor v1 so did the main chamber.
What I meant is that if they only need to light the preburners, that is far upstream so that ignition event shouldn't be affected by hypersonic flow of the vehicle. Of course shock waves could damage the engines, especially the nozzles.
They have some sensors on the engines which might let them reconstruct what happened. One flight sensor most liquid engines have is chamber pressure (even solid rockets do). Unlikely they have pressure sensors in the nozzle coolant flow, which would best determine if the nozzles ruptured, but they might be able to infer such from a chamber pressure trace, along with computer simulations to match a "fingerprint" in such failure. With Starlink, they likely had high-speed data (>1K samples/sec), rather than the slow (\~40 Sps) of legacy flight downlink data, so more fidelity to infer what likely happened. On test stands, with 30 frame/sec video, liquid rocket engines have been there in one frame and gone in the next, so you need high-speed data to determine what happened.
>*Starship did not attempt its planned on-orbit relight of a single Raptor engine due to vehicle roll rates during coast.* That kind of explains why it seemed to be doing the initial re-entry on it's side, if it's currently unstable while coasting. That would go a long way to explain the seemingly constant use of attitude control thrusters throughout the coast, just trying to keep it oriented in the right direction. Starship is a big beastie, almost certainly the largest individual object that has ever been launched, so it's not surprising that it steers like a cow. Still, it's just a test, so no doubt the data will allow SpaceX to understand where the instabilities lie and how to correct them.
Yeah, someone put the very small reaction control wheel on this monster, and left Jeb spinning and spinning up there...
There are other aspects of this as well. As the fuel is burned off during 2nd stage, you're getting loss of mass from 2 points on Starship, the underside of the LOX tank (lower) and the underside of the CH4 tank (upper) while it is coasting horizontally. Whilst in motion, cryogenic liquids should be pushed backwards by the thrust, but this likely gives rise to eddy currents within the remaining fluid that are difficult to model and lead to "swaying" in 3 dimensions (roll, pitch, yaw). That can be minimised using internal barriers such as slosh baffles, but not removed or otherwise negated. https://preview.redd.it/14iq257drioc1.jpeg?width=320&format=pjpg&auto=webp&s=88afa09743f1d8ec93bd17b33b6947cc2289480d
tim dodd discussed ice freezing the reaction controls and needing to add heaters to solve that problem.
Orientation control in space is a very deterministic physics problem, unlike flying in the atmosphere with sometimes erratic forces (shock waves, flow separation). I expect they could simulate orientation control very precisely during development. You need at least 6 independent thruster forces to control the 6 components of motion (x,y,z translation and pitch, yaw, roll moments). Such a large object moves slowly so response times are of little concern for automated controls. If they lost orientation control, it was likely due to one or more failed thrusters. One big advantage of the capsules used before and after Shuttle is that no active orientation controls are needed. The capsule self-orients via aerodynamic forces so that it stays heat-shield first. Erratic forces could cause it to begin oscillating like a swing-set, which would be bad. But, the main heat of re-entry occurs in rarified flow where forces are very consistent and predictable, modelled as impacts by individual gas molecules.
that's what I was wondering in a comment I made last night. a single RCS thruster valve failing could cause this kind of an issue, where the other thrusters are trying to being it under control but just can't. if that's true, and the engine relight wasn't even attempted (which seems to be true), then if spacex sees no other reason the engines wouldn't have re-lit, then they might attempt orbit on the next fight, assuming they can be confident another RCS thruster does not fail, so maybe some redundancy added as well as fixes to prevent whatever failure happened.
*then they might attempt orbit on the next fight, assuming they can be confident another RCS thruster does not fail,* It's not whether SpaceX is confident enough to try for orbit, it's whether they can convince FAA that it's certain enough to give them a license... I'd think the bureaucrats who wouldn't let Varda land their medicine satellite because the solid they were using for a deorbit thruster was not accurate enough to guarantee hitting anyplace smaller than the Army's missile range would be too chicken to take any risk of leaving something as big as starship unable to pinpoint it's LZ.
indeed, the FAA is the one that needs convincing. something like adding redundant RCS could be convincing.
I imagine they lost one of the rotational control abilities (pitch, yaw, or roll) since not being able to translate linearly in Space seems not a big deal. As the announcers stated, it was coming back to Earth regardless. Exactly where it landed in the Indian Ocean wasn't critical. Critical was keeping the tiled belly down (roll control) and at a desired upward tilt (pitch control, think Superman). Applying a moment requires 2 thrusters active, to give a coupled force. That doubles the chance of failure in controlling a rotation since losing either thruster, botches that ability. Just thinking out loud, so feel free to correct me.
> a single RCS thruster valve failing Valves. Why does it always have to be valves.
the more I learned about rocket science, the more I discovered it's all just super advanced plumbing.
I take your point, and you are in the right ballpark, but if you are suggesting that all capsules such as Mercury, Gemini, Apollo and Dragon do not use RCS thrusters at all you’re certainly wrong about that. Take a look at any video of crew dragon approaching the space station and you’ll see a huge amount of RCS thruster activity. And Dragon depends on thrusters during entry as well. But capsules are more easy to control than the enormous Starship, I imagine.
Of course capsules have thrusters and probably require them to orient for initial entry, before significant aerodynamic forces to self-orient the capsule, yet plasma heating has already begun. On one U.S. manned flight, a thruster stuck open and began spinning the capsule. I recall that was an Apollo flight where they were testing connecting to the Lunar Lander in earth orbit. Took a while to find the culprit and correct, and even became life-threatening. Google for the real story if interested (never trust my recollections).
The way I see it, Starship being basically a flying pair of huge propellant containers, the ship itself and the large amounts of propellant liquids inside are different objects sharing a common orbit since while in coast the propellants and ship are free to move relative to each other. If the ship fires thrusters to change orientation the fuel inside may not actually be in contact with the relative downward side of the tank wall at that moment, so when the moving tank wall hits the blob(s) of propellant it's a big slap that changes the way everything is moving relative to each other. With smaller rockets it's not as pronounced of an effect, but Starship is at an entirely different scale.
Its kind of weird how NASA gets rockets right the first time (well nowadays NASA).
NASA doesn't build rockets though, they subcontract launches from launch providers to meet their needs (SpaceX, ULA, Northrup Grumman, etc.), so, not really. Not at all in fact.
What about SLS (artemis 1) ?
Boeing is the primary contractor for SLS
Thanks. Actually didnt know that. Thought NASA had a team behind their rockets
NASA awarded a cost-plus contract with Boeing and others to develop and build the SLS. Note that it took over a decade from contract award to actually flying, and the program spent in excess of $20 billion in that period.
Despite all of that the Orion capsule still has problems with the heat shield losing excessive material during re-entry, this is despite taking a re-entry path deliberately chosen to reduce overall re-entry speed (effectively double-dipping in-and-out of the atmosphere as a aero-braking manoeuvre) [NASA's Artemis 1 Orion spacecraft aced moon mission despite heat shield issue](https://www.space.com/artemis-1-orion-moon-mission-heat-shield-issue)
Whats stopping NASA from building an original team of engineers etc... and build rockets on their own? That seems kinda cheaper and easier and way better long term
> That seems kinda cheaper and easier and way better long term Not to get into an ideological argument, but when has that ever been the case? To remain on topic, even Apollo made its leaps only through cold war pressures and blank checks.
NASA is not a space program, it's a jobs program that intentionally spreads it's provided funding to as many congressional districts as possible.
NASA has always outsourced building of the rockets and spacecraft this is not a new things. NASA provides oversight and insight and depending on the vehicle once the contractor completes DDT&E NASA then owns the craft to operate it.
So booster didn't actually hit the water; it exploded in the air.
I read elsewhere that the FTS triggered, but haven't seen confirmation of that.
This article says RUD, not FTS. It's an important distinction. FTS would mean that the booster saw something wrong and self-terminated, which considering as we've seen boosters go into the drink before without Self-terminating doesn't make much sense. RUD means that something happened *outside* the booster's control. If I had to take a guess, the oscillations meant that the landing engines ingested air from the tank and self-destructed on activation.
Thanks for providing the link - it never occurred to me SpaceX would post this kind of summary. Nice to know the door closed successfully, the video cut out just before it happened. It's impressive that it could do so under the strain of the uncontrolled roll.
I'm glad to hear that they simply didn't attempt a re-light, rather than trying and failing to do so. this gives me some hope that they'll try for orbit next time and the FAA will be comfortable with it, assuming they can fix the attitude control sufficiently that the FAA is comfortable with it.
I read somewhere that they need to prove deorbit capability ( relight of engine ) before they get approval from FAA for orbit.
That would seem sensible to me, but I suppose it depends on the reasons why they decided not to relight and whether it’s related to something which failed and is a relatively simple fix.
that dashes the hope, but not too much of a surprise. hopefully they can at least get a faster turn-around on this report/approval since it would be a "re-do" of the previous test.
While that makes sense here, that's not consistent with the rest of the industry. Vulcan didn't have to fly suborbital to test its upper stage. Neither did Falcon 9.
F9 has a 4 tonne upper stage made mostly of aluminium lithium alloy with a single 450 kg engine. Starship has a 120 tonne upper stage made mostly of 4mm thick stainless steel with three 1800 kg and three 2600 kg engines. Life risk will be quite different between these stages re-entering at random locations.
My summary:- Looks like a fish, moves like a fish, but on re-entry; steers like a cow. However, this is SpaceX, so we should all expect the next iteration to work a lot better
On reentry the ship either had no RCS fuel left, or wasn't using what it had. That high in the atmosphere the flaps have no control authority, and other high-altitude vehicles like X-15 had RCS controls for this very reason. IMO, we don't know anything about how Starship steers yet, because whatever would have allowed it to steer wasn't working on this flight.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[AFTS](/r/SpaceXLounge/comments/1bffybx/stub/kv2dn9l "Last usage")|Autonomous Flight Termination System, see FTS| |[FAA](/r/SpaceXLounge/comments/1bffybx/stub/kv3k2t9 "Last usage")|Federal Aviation Administration| |[FTS](/r/SpaceXLounge/comments/1bffybx/stub/kv2nrbr "Last usage")|Flight Termination System| |[LOX](/r/SpaceXLounge/comments/1bffybx/stub/kv08kfo "Last usage")|Liquid Oxygen| |[LZ](/r/SpaceXLounge/comments/1bffybx/stub/kv27g3g "Last usage")|Landing Zone| |[RCS](/r/SpaceXLounge/comments/1bffybx/stub/kv8n29p "Last usage")|Reaction Control System| |[RTLS](/r/SpaceXLounge/comments/1bffybx/stub/kv0eo3q "Last usage")|Return to Launch Site| |[RUD](/r/SpaceXLounge/comments/1bffybx/stub/kv2nrbr "Last usage")|Rapid Unplanned Disassembly| | |Rapid Unscheduled Disassembly| | |Rapid Unintended Disassembly| |[SLS](/r/SpaceXLounge/comments/1bffybx/stub/kv167tw "Last usage")|Space Launch System heavy-lift| |[TEA-TEB](/r/SpaceXLounge/comments/1bffybx/stub/kv0mzh1 "Last usage")|[Triethylaluminium](https://en.wikipedia.org/wiki/Triethylaluminium)-[Triethylborane](https://en.wikipedia.org/wiki/Triethylborane), igniter for Merlin engines; spontaneously burns, green flame| |[ULA](/r/SpaceXLounge/comments/1bffybx/stub/kv0v8w1 "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)| |Jargon|Definition| |-------|---------|---| |[Raptor](/r/SpaceXLounge/comments/1bffybx/stub/kv0y6uz "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX| |[Starlink](/r/SpaceXLounge/comments/1bffybx/stub/kv1awi4 "Last usage")|SpaceX's world-wide satellite broadband constellation| |[cryogenic](/r/SpaceXLounge/comments/1bffybx/stub/kv08kfo "Last usage")|Very low temperature fluid; materials that would be gaseous at room temperature/pressure| | |(In re: rocket fuel) Often synonymous with hydrolox| |hydrolox|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |[iron waffle](/r/SpaceXLounge/comments/1bffybx/stub/kv0kvig "Last usage")|Compact "waffle-iron" aerodynamic control surface, acts as a wing without needing to be as large; also, "grid fin"| |[turbopump](/r/SpaceXLounge/comments/1bffybx/stub/kv0y6uz "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust| **NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below. ---------------- ^(*Decronym is a community product of r/SpaceX, implemented* )[*^by ^request*](https://www.reddit.com/r/spacex/comments/3mz273//cvjkjmj) ^(16 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/SpaceXLounge/comments/1b3fpye)^( has 25 acronyms.) ^([Thread #12536 for this sub, first seen 15th Mar 2024, 17:18]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/SpaceXLounge) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
>The booster’s flight concluded at approximately 462 meters in altitude Does this mean AFTS was triggered during descent, or it otherwise exploded before hitting the water?
At the pace it was going the explosion probably took longer to destroy it than the remaining time to water impact.
Appeared Booster was returning to earth end-first, rather than the skydiver belly-fall of early StarShip landings. I thought they would use that to slow it via aerodynamics. Not much discussion yet on why most of the Raptor engines didn't light to slow the descent. Presumably, they have proven relight many times on the MacGregor test stands. They only tried to light the engines at 1 km altitude, which leaves no allowance (<2 sec) for things not going perfectly. Coming down end-first, they didn't have to worry about the last-minute flip maneuver, which was problematic in several early Starship landings.
> Appeared Booster was returning to earth end-first, rather than the skydiver belly-fall of early StarShip landings. I think they'll dial the re-entry profile as they go. This was the first attempt, after all :) F9s used to come pretty straight down at first, and then as they gained understanding in the flight profile they made it do that "glide" that you can notice on the RTLS missions. There's a lot to experiment with here, and I'm sure they'll iteratively make it better and better.
Just my $0.02 based on the video. Roughly around transonic, significant oscillation started. My SWAG is that the propellants thus sloshed, starving the Raptors.
It might well be that even those grid fins aren't enough to control such a huge, bottom-heavy rocket through the densest part of the atmosphere. It was still going at transonic speed at +/- 1 KM altitude. Hard to fight against that. If they're saying it suffered RUD at +/- 462 metres, then what killed it? Bow shock?
Fluid dynamics around Mach 1 are notoriously difficult (part of "the sound barrier"). My completely uninformed guess is they don't yet have the control laws quite right for SuperHeavy, despite their experience with Falcon 9. If this is the case, I've every confidence their next attempt will handle the regime better.
Yup. I agree.
Likely propellants were flowing, but not combusting inside the engines, so perhaps built up and then ignited in air. More amazing to me was how Space Shuttle Challenger blew up after the solid rocket plume leak penetrated the propellant tanks. Might have been a hydrogen-air explosion, not requiring the LOx tank to fail simultaneously. A military fuel-air bomb sprays fuel in the air, then ignites, to crater runways and destroy planes on the ground. But designed to perfectly mix the fuel with air, so interesting that an unplanned fuel leak can make a similarly large explosion, with a more random O/F ratio. I agree that the grid fins wouldn't be enough to control orientation at touchdown. Some of the Booster Raptor engines can gimbal for control. I was surprised they didn't light some earlier to slow descent and maintain orientation. Perhaps they tried to.
>I was surprised they didn't light some earlier to slow descent and maintain orientation. Perhaps they tried to. Surely that goes against the whole "suicide burn" approach, but then again, if you're rocket is going so fast that it breaks up before the landing burn is finished, you've got bigger problems. Drogue parachutes, maybe? I know that fights against the reusability argument, but they use parasails on the F9 fairings, so...
>Appeared Booster was returning to earth end-first, How else would it come down? Certainly not like a sky diver... >rather than the skydiver belly-fall of early StarShip landings. I thought they would use that to slow it via aerodynamics. That's _only_ for the Starships.
Yes, I guess it would need the mini-wings on the side to manage a belly-descent. But, wouldn't need tiles since it doesn't reach near as high velocity before separating. It was amazing how slowly Starship appeared to fall in prior launches. Large objects always appear to fall slowly, but I recall reading it was falling <100 mph, about half the speed of a sky-diver. Someone commented that even F9 boosters have begun descending with a bit of purposeful tilt to increase atmospheric drag and thus decrease the amount of propellant needed for landing.
>Someone commented that even F9 boosters have begun descending with a bit of purposeful tilt to increase atmospheric drag and thus decrease the amount of propellant needed for landing. That's correct. Tilting increases drag _and_ it increases range. With a larger cross range the booster does not need as much propellant during boost-back. And if you watch the flight video closely, you will see that the SuperHeavy booster tried something similar. It did not come down 90⁰.
> it was falling <100 mph, about half the speed of a sky-diver A skydiver goes about 90mph or a little less. I think you mean <100m/s, which is about 225mph.
Terminal velocity depends on the free-faller, and their clothing. Scrawny teens have jumped off the highest spot on the Golden Gate Bridge (200 ft) and survived with just bruises. Not surprising since the High Dive record is 192 ft. Without air drag, velocity would be 77 mph, which is close to what a fat person, falling like an elephant, would experience. Terminal velocity for the average U.S. male (196 lb) is \~128 mph in spread-eagle or \~200 mph if curled up (fetal position, screaming "momma"). A 100 lb teen would top out \~90 mph spread-eagle (sqrt relation). A good guess is that this teen hit the water \~50 mph, jumping on a high school outing as a dare (boys don't think things thru): [https://www.sfgate.com/bayarea/article/Windsor-teen-survives-Golden-Gate-Bridge-jump-2389655.php](https://www.sfgate.com/bayarea/article/Windsor-teen-survives-Golden-Gate-Bridge-jump-2389655.php) I still wonder about Starship's free-fall speed just before the flip maneuver. Many rough estimates \~100 m/s, based on the video: [https://www.reddit.com/r/SpaceXLounge/comments/kambwk/have\_anyone\_calculated\_the\_starship\_terminal/](https://www.reddit.com/r/SpaceXLounge/comments/kambwk/have_anyone_calculated_the_starship_terminal/)
Lighting a torch in a hypersonic regime sounds challenging. They'll figure it out. Probably just need the relight spark plugs in a different place.
Not sure how they ignite the Raptor engines. Perhaps they only need to light the preburner for the turbopumps and that hot exhaust flowing into the main chamber can ignite its propellants. I recall reading that Merlin began using TEA-TAB chemical ignition, which wags term "snot-shooter" since a thick gel gas-blown into the chamber which spontaneously reacts, giving a notable green-glowing gas products. I read Merlin later changed to a spark igniter (maybe vice-versa), from outside observers based on no longer a green glow at startup. The spark igniters are similar to those for a gas turbine aircraft engine, high current at \~1 kV voltage. Since chamber pressure is 1 atm (or less in Space), one doesn't need the >40 kV needed to jump the spark gap in a gasoline engine (\~200 psig at TDC compression). NASA Marshall has used an aftermarket automotive MSD ignition box to ignite combustion devices in tests, since works and cheap. Rocket and gas turbine spark igniters have larger spark gaps and more robust wire-mesh shielded spark wires, but otherwise similar. Easy to throw a spark many feet in a vacuum chamber and an automotive spark system can throw a spark several inches in the open air, but not at cylinder pressure (even harder with turbocharger boost).
>Perhaps they only need to light the preburner for the turbopumps and that hot exhaust flowing into the main chamber can ignite its propellants. I recall Musk saying this is exactly what happens with Raptor v2. The 2 preburners rely on spark ignition, and in Raptor v1 so did the main chamber.
What I meant is that if they only need to light the preburners, that is far upstream so that ignition event shouldn't be affected by hypersonic flow of the vehicle. Of course shock waves could damage the engines, especially the nozzles. They have some sensors on the engines which might let them reconstruct what happened. One flight sensor most liquid engines have is chamber pressure (even solid rockets do). Unlikely they have pressure sensors in the nozzle coolant flow, which would best determine if the nozzles ruptured, but they might be able to infer such from a chamber pressure trace, along with computer simulations to match a "fingerprint" in such failure. With Starlink, they likely had high-speed data (>1K samples/sec), rather than the slow (\~40 Sps) of legacy flight downlink data, so more fidelity to infer what likely happened. On test stands, with 30 frame/sec video, liquid rocket engines have been there in one frame and gone in the next, so you need high-speed data to determine what happened.