Starship Flight 5: Launch and booster catch [video] • Hacker News Board

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

#371

Post by azernik » Sun, Oct 13, 2024, 4:33 PM UTC

cubefox wrote: post #285

adt2bt wrote: post #99

Earlier quoted context omitted.

Think of the word ‘reusable’ in this case as less a binary descriptor but more of a scale of reusability. Yes, both systems are reusable, but there are key differences in the refurbishment of the systems that partly explains the cost difference. It took more labor, resources and time to refurbish the shuttle. Also consider rapid reusability was a stretch goal when it was being designed, but we have come a loooong way…

> Yes, both systems are reusable, but there are key differences in the refurbishment of the systems that partly explains the cost difference. It took more labor, resources and time to refurbish the shuttle. Starship uses essentially the same ceramic heat shield tiles as the Space Shuttle, so the fact the Shuttle had so much trouble with refurbishment doesn't mean that SpaceX has solved these refurbishment issues with…

The tiles are very similar; the attachment system is very different (a big part of why Shuttle's were a pain to maintain) and Starship's simple shape means most of the tiles are the same (the ridiculous number of SKUs was another factor in Shuttle TPS costs).

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

#372

Post by lpribis » Sun, Oct 13, 2024, 4:34 PM UTC

brcmthrowaway wrote: post #348

Does each engine have 6 degree of freedom to point its jet?

No, each individual engine has 2 DoF (x-axis and y-axis rotation) which correspond to torque on x and y plane to the rocket. They need to use more than one at once (three in starship's case) pointing in different directions to get z axis torque.

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

#373

Post by Alex-Programs » Sun, Oct 13, 2024, 4:35 PM UTC

nebben64 wrote: post #304

kevinmhickey wrote: post #259

Earlier quoted context omitted.

It’s the hot staging spacing ring. They didn’t call it on the feed but it is an expendable part that ejects after separation.

thank you!

Hotstaging was added quite late so they need to jettison in order to land, but it should be permanently integrated in the later variants.

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

#374

Post by itishappy » Sun, Oct 13, 2024, 4:35 PM UTC

quotemstr wrote: post #308

augusto-moura wrote: post #226

Earlier quoted context omitted.

I don't think we have a number for it yet. But it will definitely be the cheapest launch system at the time of launch. People say 200$/kg just with booster reuse, and 20$/kg with full reuse. Of course this might be too optimistic, but I truly believe we might reach under 50$ in this decade.

Even $50 is within "going to the moon for my honeymoon" range. Wow.

Only if you don't care about coming back!

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

#375

Post by pclmulqdq » Sun, Oct 13, 2024, 4:36 PM UTC

dotnet00 wrote: post #60

Waterluvian wrote: post #50

Earlier quoted context omitted.

Is that 150t of payload or total? What’s the cost in fuel alone (let’s ignore maintenance and operations costs for now)? I’m trying to get a feel for the relative scale compared to today’s commercial flight.

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.

None of the vehicles have demonstrated any payload capacity yet. 50 tons is the on-paper capacity only, and seems quite high given how little fuel is left when the bring an empty starship to orbital altitude. I assume that as the engines and launch procedures get more efficient, they will start being able to bring stuff to orbit (and quite a bit of stuff, too).

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

#376

Post by wildzzz » Sun, Oct 13, 2024, 4:36 PM UTC

arijo wrote: post #323

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-…

> Another interesting thing SpaceX is doing is to use consumer-grade chips in triple redundancy configurations instead of using $100,000+ radiation-hardened aerospace/defense grade chips. This has been known in the high availability and safety systems industry for a while and a good book to learn these reliability engineering techniques is "Reliability Evaluation of Engineering Systems". The book is available on amaz…

One downside of using non-rad hard parts is degradation from TID (gamma) and latch up effects. You can have chips monitoring other chips to reset whenever they latch up but TID is mostly permanent. The good thing is that TID in LEO, where SpaceX mostly operates, is relatively lower than GEO so they can get by with mostly commercial parts. It's not like the big defense contractors haven't figured out the same thing, they do fly stuff using commercial parts as well, they are just slower to adopt the same culture. SpaceX and the companies that built components using commercial parts are building the new-space industry.

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

#377

Post by WalterBright » Sun, Oct 13, 2024, 4:36 PM UTC

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-…

Reliability is not based on a system that cannot fail. It is based on a system that can survive failure.

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

#378

Post by shellfishgene » Sun, Oct 13, 2024, 4:36 PM UTC

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.

The simulation they show at 21 min into the video is almost exactly like it happend in the end, to it seems it went perfectly as planned.

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

#379

Post by stetrain » Sun, Oct 13, 2024, 4:38 PM UTC

justin66 wrote: post #344

stetrain wrote: post #234

Earlier quoted context omitted.

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.

Yes, for most of the booster return it’s ‘gliding’ with the rocket engines completely shut down.

They ignite a subset of engines just a few seconds before landing for the final slowdown and maneuvering.

Edit: here is a video from further away that shows the rocket gliding in under control of the grid fins before the engines light and execute the final landing maneuver:

https://x.com/shaunmmaguire/status/1845444890764644694

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

#380

Post by hobofan » Sun, Oct 13, 2024, 4:39 PM UTC

foobarian wrote: post #235

autonomousErwin wrote: post #16

That was crazy, 50% of me thought as it was coming in, especially as it pitched towards the tower, "they've overcompensated and are going to bring the whole tower down" but they absolutely nailed it.

Even without the catch step, I always feel like their boosters are coming down way too fast way too late, with engines reigniting startlingly close to surface. Never ceases to surprise me.

Yeah, it also always catches me off guard how late they reignite, while at the same time I'm always surprised by how slow the liftoff is even though all the boosters are on full throttle. Of course both things make sense given the respective mass at both points in the process, but given that it looks like the same rocket from the outside, a bit unintuitive.