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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]

#481

Post by mlsu »

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 know MPC takes a LOT of compute power. It's not like a finely tuned PID loop or even a cascade of PID loops, computationally.

Does anyone know (or have educated speculation on) what kind of hardware is running these algorithms? Like, do they have a linux machine that's running the control loops? Are we talking megabytes, gigabytes of SRAM?

I would think no -- you would definitely need hard real time for something like this. But my only experience with real time systems is in tiny MCUs with kb of SRAM. That's definitely too small for a controller like this.

Really curious about the nuts and bolts of this.

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

#482

Post by WalterBright »

api wrote: post #240
shirro wrote: post #199

Earlier quoted context omitted.

Second stage reuse seems the far more challenging problem. Other companies should have reusable boosters soon but if significant amounts of Starship continue to ablate on the way down they could be faced with a disposable Starship competing with smaller and cheaper second stages that are well sized for typical payloads. We already knew boosters can be flown back to launch sites reliably with high accuracy. We don't k…

Didn’t they look at all kinds of ideas earlier like squirting some propellant or water out over the skin on the way down, and wasn’t steel chosen for its thermal robustness? Did they get into the problem and realize it’s a lot harder and abandon those things for tiles? Maybe they will have to sacrifice more payload mass for active or passive shielding or more fuel for powered deceleration. That would yield a less imp…

Interestingly, the inside surface of a rocket nozzle is covered with tiny holes. Fuel is circulated in a jacket around the nozzle both to pre-heat the fuel and to cool the nozzle. Additional cooling of the nozzle comes from fuel leaking into the combustion chamber through those holes, carrying away the heat so it doesn't melt the nozzle. It's called boundary layer cooling.

It was one of the technological breakthroughs of von Braun's team with the V2.

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

#483

Post by coding123 »

XorNot wrote: post #96
ptek wrote: post #52

Very inspiring, glad I woke up to watch it. Congratulations to the SpaceX team. This is what competition looks like. It’s funny how last decade SpaceX had to sue the government to get more launches.

The FAA needs more funding at this point. They're not staffed for the rate of launch requests which commercial space has grown too.

Or dismantled, lol

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

#484

Post by mrandish »

moffkalast wrote: post #336
h2odragon wrote: post #177

My wife asked "Why is this a big deal?", so I gave her a link to Handmer's 2021 explanation: https://caseyhandmer.wordpress.com/2021/10/28/starship-is-st... She's not an enthusiast; she's got an impression from SciFi that going to mars shouldn't be that hard.

Well I mean going to Mars isn't that hard per se, a fair few countries have done it... but carrying enough supplies and shielding to last people 2 years until the return trip and then actually getting back are way harder problems. Seeing Starship get burnthrough on these suborbital launches really shows how hard it'll be to do Mars return entry with a fair few extra km/s.

Getting to Mars is hard but not that hard compared to getting a large payload to Mars surface and back to Earth. Some people may assume Mars return is around twice as hard but it's orders of magnitude harder. And that's before even contemplating doing so with a cargo of humans and the necessary tonnage for them to survive on Mars at least 26 months.

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

#485

Post by tempestn »

zitterbewegung wrote: post #194
aaronharnly wrote: post #25

Earlier quoted context omitted.

Naive question: I obviously expect there to be flames from the engines, but there were flames on the lower sides for quite a while after the catch – is that expected?

They have mission goals which were achieved (booster was caught). Goals that they didn't think they could do (Starship being within the buoys). While there was flames and those could be dangerous you judge the mission based on the planned outcomes but they will try to eliminate the anomalies to improve the next mission while still achieving the goals.

The thing is that no one is judging the mission based on this imperfection. It's just intellectual curiosity, which is a good thing. The comments that are getting down voted are all assuming some negative motive that just isn't present.

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

#486

Post by andrewstuart2 »

WalterBright wrote: post #479
philistine wrote: post #352

Earlier quoted context omitted.

> Other companies should have reusable boosters soon You're way too optimistic. Starship will deliver commercial payloads, with SpaceX phasing out Falcon 9 outside of ISS launches, before anyone has a reusable Falcon 9 equivalent. It pains me to say this, but SpaceX is in a class all its own.

Why does it pain you? Musk's SpaceX has produced several enormous advancements in space technology. SpaceX is one of the greatest, if not the greatest, private technology company in history.

I think it pains some of us to say it because of the person Musk has turned out to be, which is the opposite direction I think many of us were hoping his character development would take him.

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

#487

Post by WalterBright »

ptek wrote: post #52

Very inspiring, glad I woke up to watch it. Congratulations to the SpaceX team. This is what competition looks like. It’s funny how last decade SpaceX had to sue the government to get more launches.

California officials reject more SpaceX launches, with some citing Musk's X posts

https://twitter.com/shellenberger/status/1845131546501734440...

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

#488

Post by mlyle »

mlsu wrote: post #481
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 know MPC takes a LOT of compute power. It's not like a finely tuned PID loop or even a cascade of PID loops, computationally. Does anyone know (or have educated speculation on) what kind of hardware is running these algorithms? Like, do they have a linux machine that's running the control loops? Are we talking megabytes, gigabytes of SRAM? I would think no -- you would definitely need hard real time for something l…

MPC doesn't need to take a ton of compute power. It all comes down to how sophisticated the underlying model is. You can have a MPC with 20 variables and run it at multiple kilohertz on a tiny microcontroller.

When you build something like this, you're torn between having a big model that represents everything and a smaller model that is easier to validate and reason about. Based on simulation, you might go for a smaller model that "knows" to stay away from operating areas where hidden variables (like really complicated tank slosh) invalidate the small model.

I doubt the actual control loop is too much processing, but it's certainly possible to build controllers with SDRAM, millions of variables of state, and hard realtime processing, though I wouldn't build it on top of preempt-rt. ;)

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

#489

Post by sebzim4500 »

macintux wrote: post #452
mlindner wrote: post #409

Earlier quoted context omitted.

They do this every launch unfortunately. Youtube seems completely inept at stopping them. They make enough money to hire hundreds of thousands of fake accounts to subscribe.

Musk choosing to abandon YouTube to push his other company didn’t help.

True, but even before that there were fake spacex streams (complete with a 'verified account' symbol) with 10k+ alleged viewers.

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

#490

Post by sebzim4500 »

perlgeek wrote: post #448

During/before the water landing of Ship, the telemetry indication for the rocket motors stayed off. Does that mean the landing burn was unsuccessful? Or was that just a glitch in the telemetry?

It's weird, that happened last time too so you'd think if it was a glitch they would have fixed it.
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