Completely. The relevant technology for Starship heat shield would be Dragon, though one could imagine there's still quite a bit involved to get from Dragon to Starship...
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Completely. The relevant technology for Starship heat shield would be Dragon, though one could imagine there's still quite a bit involved to get from Dragon to Starship...
Can you imagine the motion sickness those maneuvers would cause? I used to get air sick when I was a kid, can’t imagine how I would feel in Starship moving like that, lol. I would absolutely do it (once they’ve got a track record of reliability, of course) since saving hours to even a whole day of flight time would be amazing, but I’d be curious to know how they’re planning on handling that. Maybe gimbaling seats so passengers are always in the same orientation relative to gravity no matter how the Starship moves?
The question I have is whether the landing was supposed to be a three engine suicide burn. It sure seemed that way. Each engine lights up in a sequence with the two doing the flip being first. The third that didn't light was probably would have done that final rocket length of slowing. The second engine cutting out was the final straw and even then it was pretty close.
Go SpaceX. It was awesome.
Go SpaceX. It was awesome.
Is it truly a "relatively easy fix"? They've had years to design and simulate the horizontal environment and it failed on the first try. This scheme, switching tanks and feeds, seems to go against Musk's statement that "no part is better". I'd rather them concentrate on making the existing aero surfaces do most the rotation to vertical so they can use the main tanks for prop. They're already taking the mass hit lugging those surfaces everywhere, why not use them where it matters most (landing, because a failed landing is worse than using expendable stages).
I really liked the stable skydive portion. What motors did they use for the flippers? Tesla motors?
Didn't most of the test tiles fall off on a recent test? I don't remember if it was one of the hops or static fires.Also, doesn't this go directly against your first paragraph where they didn't get the tank pressures right?
I guess I'm so negative on SS because I can't get past them lugging a such huge amount of dry mass around. Every kg that returns to the Earth's surface blows up the amount of kg that needs to leave the Earth at the beginning. It's like the Shuttle all over again.
For these tests, the SS landing legs are stubby things inside the skirt. I don't think they had time to deploy ... not that it would have made a difference today. No one knows what the final landing leg design is going to look like. It's a surprisingly difficult problem.
The ship is supported by the mount prior to launch, not the landing legs.
petit_bateau
Active Member
This was fantastically successful imho. Very good stable control through all phases of flight, with various engine-out tests apparently executed (see below), except for insufficient deceleration at the end.
Some questions/observations if anyone can respond that would be nice.
Using the SpaceX timer on the video at
I have some questions, and I don't think Elon's tweets really answer them definitively.
=======
01:40 = first engine out (the left one), notably immediately preceded by a reduced thrust which can be seen from the way the other two engines gimbal to compensate. Appears to be operating fine until this point. Question : was this a deliberate engine-out test ? My suspicion is that this was deliberate, but it would be nice to know. Can anyone confirm ?
01:50 = flames evident in the right section of the engine bay. Previously there have been flickering reflections in the bay which were probably (but not conclusively) reflections of the nozzle flames. However the 01:50 flame is definitely not that. Anyone know what it is ?
01: 50 = commencing at the same time the external shot has white smoke/gas trailing from the skirt of the engine bay area. Anyone know what this is ? It could be a depressurisation vent of the non-operational engine feed lines, or it could be fire.
01:59 - 02:14 = some gas jets from the upper right section inside of the engine bay. Anyone know what this is ?
03: 13 = right engine switched off, appears to me to be operating fine until that point. As before flameout is preceded by loss of thrust and compensating gimballing by centre engine. Question : was this a deliberate engine-out test ? My suspicion is that this was deliberate, but it would be nice to know. Can anyone confirm ?
03: 13 = there are now two separate white smoke / gas origins from the skirt area ? Same question as before - deliberate venting ?
03:45 = first use of the RCS that I can observe, from the mid-body RCS jets. Does anyone know what the manoeuvre/test objective was at this point ?
04:26 = second RCS pulse, mid-body again. Does anyone know what the manoeuvre/test objective was at this point ? A much longer RCS burn, perhaps
04:28 = a lot more skirt smoke/vent gas again, what is it?
04:30 = actuators on fins start operating,
04:38 = centre engine out, with a bit of a combustion 'pop' as it went out. This was not the same behaviour as the other engine-outs. Did it cause any damage as it was switched off ?
04:38 = Immediate camera feed switch to double fin, so it seems very likely this was a sequenced event. All fin actuators now operating for bellyflop. Nose and mid-body RCS all operating for the flip over. Good co-ordination even though likely falling tail first at beginning (i.e. reversed controls). Roll axis stable - I wonder how the pumps are oriented and to what extent gyroscopic effects are being controlled for. (*)
04:40 = trailing smoke/vent gas = same question, what is it ?
05:00 = very stable, trivial oscillations in pitch and roll, nicely controlled
06:20 = going nose up as falls through the cloud layer, starting to orient for ignition
06:29 = switch camera views to engine bay for reignition
06:30 = relights, looks to me as if only left and right relight, not centre, then green-out & crash. If you look at each of the previous engine-outs you will see that an engine does not actively gimbal unless it is lit and operating, and I do not on this occasion see the centre engine start gimballing. Exactly what did happen to each of the three engines and why ? More particularly why did the centre engine not relight ?
06:42 = impact, not quite sufficiently decelerated. Precisely position as far as I could see.
regards, pb/dspp
-----
* these are some of the issues that Yeager encountered, but did not understand/accept/whatever, see Bob Smith's account of the NF-104 and Yeager at NF104 | Yeager's View in Review . We are now able to incorporate the lessons identified by Smith et al after all this time. Fantastic.
Some questions/observations if anyone can respond that would be nice.
Using the SpaceX timer on the video at
=======
01:40 = first engine out (the left one), notably immediately preceded by a reduced thrust which can be seen from the way the other two engines gimbal to compensate. Appears to be operating fine until this point. Question : was this a deliberate engine-out test ? My suspicion is that this was deliberate, but it would be nice to know. Can anyone confirm ?
01:50 = flames evident in the right section of the engine bay. Previously there have been flickering reflections in the bay which were probably (but not conclusively) reflections of the nozzle flames. However the 01:50 flame is definitely not that. Anyone know what it is ?
01: 50 = commencing at the same time the external shot has white smoke/gas trailing from the skirt of the engine bay area. Anyone know what this is ? It could be a depressurisation vent of the non-operational engine feed lines, or it could be fire.
01:59 - 02:14 = some gas jets from the upper right section inside of the engine bay. Anyone know what this is ?
03: 13 = right engine switched off, appears to me to be operating fine until that point. As before flameout is preceded by loss of thrust and compensating gimballing by centre engine. Question : was this a deliberate engine-out test ? My suspicion is that this was deliberate, but it would be nice to know. Can anyone confirm ?
03: 13 = there are now two separate white smoke / gas origins from the skirt area ? Same question as before - deliberate venting ?
03:45 = first use of the RCS that I can observe, from the mid-body RCS jets. Does anyone know what the manoeuvre/test objective was at this point ?
04:26 = second RCS pulse, mid-body again. Does anyone know what the manoeuvre/test objective was at this point ? A much longer RCS burn, perhaps
04:28 = a lot more skirt smoke/vent gas again, what is it?
04:30 = actuators on fins start operating,
04:38 = centre engine out, with a bit of a combustion 'pop' as it went out. This was not the same behaviour as the other engine-outs. Did it cause any damage as it was switched off ?
04:38 = Immediate camera feed switch to double fin, so it seems very likely this was a sequenced event. All fin actuators now operating for bellyflop. Nose and mid-body RCS all operating for the flip over. Good co-ordination even though likely falling tail first at beginning (i.e. reversed controls). Roll axis stable - I wonder how the pumps are oriented and to what extent gyroscopic effects are being controlled for. (*)
04:40 = trailing smoke/vent gas = same question, what is it ?
05:00 = very stable, trivial oscillations in pitch and roll, nicely controlled
06:20 = going nose up as falls through the cloud layer, starting to orient for ignition
06:29 = switch camera views to engine bay for reignition
06:30 = relights, looks to me as if only left and right relight, not centre, then green-out & crash. If you look at each of the previous engine-outs you will see that an engine does not actively gimbal unless it is lit and operating, and I do not on this occasion see the centre engine start gimballing. Exactly what did happen to each of the three engines and why ? More particularly why did the centre engine not relight ?
06:42 = impact, not quite sufficiently decelerated. Precisely position as far as I could see.
regards, pb/dspp
-----
* these are some of the issues that Yeager encountered, but did not understand/accept/whatever, see Bob Smith's account of the NF-104 and Yeager at NF104 | Yeager's View in Review . We are now able to incorporate the lessons identified by Smith et al after all this time. Fantastic.
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It was meant to be two engines.
All the engine shutdowns on ascent were planned and it was hovering/ still climbing with only one running.
The thrust of three engines would have been too much for the remaining weight/mass (mass for deceleration, weight for countering gravity).
The engines were starved of fuel which reduced their thrust and total delta-v which resulted in greater than 0 velocity at 0 altitude.
petit_bateau
Active Member
mongo,
I get that the deep-throttling capability restrictions are such that a three-engine landing might be too thrusty at this landing mass. If so then your hypothesis that only two engines were intended to operate for the landing burn would be correct. However do you have evidence to support this hypothesis ?
regards,
dspp/pb
Well then we sure won't be able to at this point
.Regarding the vapor trails, I suspect they kept the engines chilled for the relight events.
Yes, they said the header tank pressure was too low (for whatever reason). Either they had a leak, or insuffucent pressurization gas (it's not autogenous yet).
Trying to use flaps for the flip won't work for the following reasons:
- For Moon and (mostly) Mars: Flaps are useless and they need propulsive landing
- For Earth: Once the ship starts turning, the crosssection is hugely reduced and terminal speed increases. Compare SN8 fall rate to an F8 booster.
- Increaed speed means more fuel/thrust/time/altitude is needed to cancel the speed.
- Flap authority is greatest when horizontal and falls as the ship goes toward vertical.
Yes, with modified output mechanisms.
Only the header tanks, and super heavy doesn't have header tanks nor heat shield tiles.
Side note, I think it has been said that, without payload, Starship can be single stage to orbit(al test).
If they used a different material (like carbon fiber), then they would have to lug around the mass of a much more effective heat shield. SS is actually stronger at cryo temps.
Then there are the cost and assembly speed aspects which make SS practical for a fleet, even if mass per ship is reduced (or fuel per launch is increased).
Elon has Tweeted at least twice that the engines did great and confirmed the ascent shutdowns were planned. That says to me if it was meant to be a three engine flip/ landing, we would have seen the third engine gimballing similarly to the other two and at least attempt to light (there was fuel + pressure at that point)
Futher, during ascent, the ship was hovering/climbing on one engine after climbing on two engines. Since it gets lighter all the time, this shows two engines at landing is sufficent to reduce velocity. Watching the landing, it appears the vehicle maintains speed at the end showing the engines are at reduced thrust. Full thrust on two would have allowed a safe landing (or at least deceleration, if three were intended). So I am firmly in the two engine landing camp (regardless of if three could throttle that low).
petit_bateau
Active Member
Understood, so we are both unsure - you may well be correct in your surmising. I guess more info will start to leak out, and pretty soon we will see the next one on the pad ready for the next test. From observations we will likely be able to fill in the gaps ourselves even if the company don't tell all. It is great to see this progress.
regards, dspp/pb
Additionally:
To flip, the front/ top/fore flaps need to produce a lot of drag compared the the aft ones. However, for horizontal descent, the ratio of fore and aft drag needs to match the CG location of the craft. Thus, you would end up with really big front flaps (more mass) that are mostly tucked in the entire time (to give the same drag as the current small ones).
Eric Ralph on Twitter brings up an interesting point that the final touchdown may have been planned for a single engine. Due to the clean looking shutdown and min thrust.
Twitter
Getting past the huge mass of a reusable orbiter only requires understanding the cost of putting a pound of cargo into orbit, which is much easier than the engineering and physics. That cost per lb also includes the time and expense to ready a reusable booster and orbiter for the next launch. The cost to put each lb into orbit for the shuttle system never became much less than earlier systems because booster was not reusable and the time and expense to refurbish the orbiter was huge.
Getting to Mars and beyond is only possible with full reusability. As Elon has explained with his "how much would air travel cost if the plane blew up each flight" analogy a thousand times.
All they need to do is rotate the body enough to where the remaining propellant in the main tanks covers the outlets then they can fire up the main engines with no problem. No need for header tanks, feed switching, etc. They're going to need a strong RCS system anyway, get that involved in the rotation, too.
Do we know what RCS system they're going to use?
Ah, you are eliminated the header tanks.
In a moon/ vacuume situation, there is no drag to induce an acceleration to get the fuel to cover the inlets. They could use RCS like in the orbital refueling.
RCS will be autgenous use of the CH4 and O2. I think they take liquid, heat it and use that, so it still needs a wet intake.
My mistake. There will be some sort of header tanks for RCS but I have to assume they'll be smaller/simpler if they aren't used for the big Raptors on landing. Here's a thread on NSF about potential RCS on SS:
Starship Methox RCS Thrusters
You can see the mess made by trying to create a jack-of-all-trades system like SS. Sometimes you need vacuum-optimized nozzles on the RCS and mains, sometimes sea-level. Aerodynamic shapes that are useless in a vacuum. I always favor a segmented approach where each part is optimized for its task. Apollo is a prime example. Even F9 is segmented: a booster that only serves one purpose and an in-space second stage to get Dragon to orbit.
Segmentation means no meaningful reusability. I think you're missing the whole point of Starship/Super Heavy.
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