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Starship Flight 5: Launch and booster catch [video]

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Re: Starship Flight 5: Launch and booster catch [video]

#271

Post by sobellian »

autonomousErwin wrote: post #197
dtquad wrote: post #183

Earlier quoted context omitted.

MIMO and nonlinear control theories are probably some of the hardest topics in all of engineering. SpaceX control system also has to compensate for the fuel moving inside their rockets so the control algorithms probably involve some kind of fast numerical fluid simulation. Another interesting thing SpaceX is doing is to use consumer-grade chips in triple redundancy configurations instead of using $100,000+ radiation-…

I always thought the liquid sloshing would be one of the hardest to simulate (considering how chaotic fluid mechanics is). Interestingly, I think this caused the 2nd Falcon launch to fail (the LOX sloshing).

At least for the retro-propulsive landing burn, I think the modeling problem is probably aided by the high G-forces that must keep the fuel very close to the bottom of the tank. Even before re-light the booster is falling near terminal velocity (I think?), so the fuel is likely sitting at the bottom.

I think it's a huge problem when re-lighting the engines in orbit, though.

Re: Starship Flight 5: Launch and booster catch [video]

#272

Post by JumpCrisscross »

forgot-im-old wrote: post #266
dang wrote: post #506

[stub for offtopicness]

[flagged]

FYI, This is a four-time flagged comment [1][2][3][4] that’s been rebutted [4].

[1] https://news.ycombinator.com/item?id=41828032

[2] https://news.ycombinator.com/item?id=41828151

[3] https://news.ycombinator.com/item?id=41828151

[4] https://news.ycombinator.com/item?id=41828468

[5] https://news.ycombinator.com/item?id=41828048

Re: Starship Flight 5: Launch and booster catch [video]

#273

Post by thinkcontext »

lquist wrote: post #200

What does Starship reusability mean for $/kg to LEO? I know there are longer term targets of $10/kg but that supposes efficiencies that aren’t here yet. Would be helpful to understand before Starship reusability where the state of the art was in terms of $/kg to LEO and where we would be with impending Starship reusability.

The dominant variable is how often they can reuse the stages. Last I heard Musk was targeting dozens of reuses for the upper stage and hundreds for the booster. If they are short of the cost per kg goes up.

Re: Starship Flight 5: Launch and booster catch [video]

#275

Post by Torkel »

ghc wrote: post #23

Nothing could have prepared me for how that catch looked. I was sure the rocket was careening into the tower at the last second before it straightened out. The control algorithms must be incredible for the landing system to work within those small tolerances.

I thought the same, screamed out "ouch that doesn't look good!" right before the catch.

The last part of the live stream they showed footage from a different angle and there it didn't look too bad though! For sure controlled.

Scott Manley put out a tweet that they went down towards a non-tower position until they were at three engine controlled burn, and only then did the side shift.

Re: Starship Flight 5: Launch and booster catch [video]

#276

Post by arijo »

dtquad wrote: post #183
ghc wrote: post #23

Nothing could have prepared me for how that catch looked. I was sure the rocket was careening into the tower at the last second before it straightened out. The control algorithms must be incredible for the landing system to work within those small tolerances.

MIMO and nonlinear control theories are probably some of the hardest topics in all of engineering. SpaceX control system also has to compensate for the fuel moving inside their rockets so the control algorithms probably involve some kind of fast numerical fluid simulation. Another interesting thing SpaceX is doing is to use consumer-grade chips in triple redundancy configurations instead of using $100,000+ radiation-…

I never thought of using fluid dynamics in the rocket stabilization algorithm—maybe it's something that could be useful to prevent many of the accidents involving liquid-transport trucks

Re: Starship Flight 5: Launch and booster catch [video]

#278

Post by thinkcontext »

JumpCrisscross wrote: post #236
lquist wrote: post #200

What does Starship reusability mean for $/kg to LEO? I know there are longer term targets of $10/kg but that supposes efficiencies that aren’t here yet. Would be helpful to understand before Starship reusability where the state of the art was in terms of $/kg to LEO and where we would be with impending Starship reusability.

> What does Starship reusability mean for $/kg to LEO? All we can say is under $1,000/kg. Which is conservative, that limit being about two thirds that of Falcon Heavy’s theoretical cost to LEO in a reüsable configuration.

We can't give any estimate. The costs depend on how many times the stages are reused. They have targets but we don't know what will actually happen.
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