How much is heat shield different from what the Falcon goes through?
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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How much is heat shield different from what the Falcon goes through?
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?Just imagine when we get the finished Starship that is fully validated for human flight! It is going to be so epic!
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).The reason engines were eating themselves is because they didn't get the tank pressures right, so the engines weren't getting the right amount of propellant/oxidizer. Relatively easy fix now that they have the data. I mean, this is the first time anyone has put a rocket in a horizontal configuration ahead of a relight before, so something had to not quite go right.
I really liked the stable skydive portion. What motors did they use for the flippers? Tesla motors?The interesting thing to me was how slow the ship fell once it was in a horizontal configuration. I mean, that makes sense. The ship has a huge cross area thus the terminal velocity won't be very high. Making such a ship fall as stable as it did, especially considering you had liquid fuel sloshing around inside was very impressive. As were the high precision maneuvers to re-orient the ship to a landing position.
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?Yes, re-entry heat shielding is an issue, but why aren't you believing SpaceX has it solved, or mostly on their way to solving it? We aren't that far away from the super heavy booster being ready for testing which means a re-entry test won't be far behind.
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.So there aren’t landing legs like on the Falcon 9 and the Starship looked supported prior to launch. Was it intended at this point to land in a vertical stance?
It was meant to be two engines.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.
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.
I have some questions, and I don't think Elon's tweets really answer them definitively
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.
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
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).
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.
Trying to use flaps for the flip won't work for the following reasons:
So the most efficient landing involves a last second full engine gimbal suicide flip (with RCS assist) and suicide burn.
- 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.
Two Raptors ignited sequentially during the flip maneuver, followed by one engine seemingly performing a controlled - if a little violent - shutdown. The question is whether a single-engine landing burn was the plan, not talking about three engines.
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.
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.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).
Ah, you are eliminated the header tanks.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?
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: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.