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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]

#341

Post by phkahler »

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).

Maybe they just use pressure sensors to tell where the fluid is within the tank.

Even a real-time simulation should have some measurements to self correct to some degree. Otherwise it'll diverge.

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

#343

Post by alemanek »

flaburgan wrote: post #76
treespace8 wrote: post #14

I'm just so happy to see this level of progress. This another big step for opening up space. To think that one day this will be considered normal. 150 Metric tons sent on a fully reusable rocket. Thats like a 747 to space.

So, reusable is supposed to reduce the cost. But the space shuttle was reusable and it has been shutdown because it was too expensive. What is the differences between the two?

Falcon 9 has already proven that partial reusability is economical. SpaceX has dominated the entire worldwide launch industry and their competitors are nation states with no need to make a profit.

The difference is that they have already proven to be the lowest cost and most reliable launcher due to reuse. This is them lapping the industry with second stage reusability.

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

#344

Post by justin66 »

stetrain wrote: post #234
drexlspivey wrote: post #230

Earlier quoted context omitted.

The booster was falling at 4500 Km/h 30 seconds before the catch with 2-3% fuel left. How is that amount of fuel remotely enough to stop the downward momentum?

Because the rocket weighs a small fraction of what it did at launch, specifically because it only has 2-3% fuel left. Fuel is the vast majority of the vehicle weight at launch, kind of like an empty vs full can of soda.

The atmosphere does its bit to slow down the booster as well. It’d be interesting to see a plot of the power output over time on reentry but I’ve always assumed the motors aren’t doing a lot of work other than keeping the booster stable, until the very end.

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

#345

Post by Waterluvian »

pfdietz wrote: post #255
dotnet00 wrote: post #60

Earlier quoted context omitted.

They previously threw around a number of around $1M per flight, as mostly fuel costs. Also, while 150t is the target payload capacity, the current test vehicles are closer to 50t in payload capacity, there are revisions in the pipeline based on data from these test flights which will bring it up to 150t.

To put this in perspective: at 150t/launch, if a launch is $1M, then for the cost of an SLS launch (at least $2B) Starship could launch 300,000 tons, about the mass of three Nimitz-class nuclear aircraft carriers.

We could use a few of those in orbit.

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

#347

Post by chasd00 »

sobellian wrote: post #271
autonomousErwin wrote: post #197

Earlier quoted context omitted.

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.

Iirc cold gas thrusters are used before ignition to provide some acceleration to force the fuel to the bottom of the tank.

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

#349

Post by brcmthrowaway »

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.

Do the control algorithms use AI?

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

#350

Post by philistine »

cubefox wrote: post #289
HarHarVeryFunny wrote: post #133

Earlier quoted context omitted.

The Shuttle consisted of the shuttle (orbiter) itself, the external tank (not reusable), and the two boosters which could be reused after ocean recovery. The orbiter itself was slow and expensive to reuse since (among other things) all the heat shield tiles were inspected and 30-100 replaced between each launch. I don't know how much work was done to the engines between launches, but SpaceX's parts and cost reduction…

> The orbiter itself was slow and expensive to reuse since (among other things) all the heat shield tiles were inspected and 30-100 replaced between each launch. Worth noting that Starship's heat shield is very similar to the one of the Shuttle. They actually got the manufacturing method from NASA.

That's why I remain very skeptical about the easy refurbishing of Starship. Initially, way back around 2016, the plan was to vent liquids to create a cushion around the ship. That sounded more easily reusable.
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