The Tech Behind SpaceX’s New Engine • Hacker News Board

Re: The Tech Behind SpaceX’s New Engine

#91

Post by avmich » Wed, Feb 13, 2019, 9:27 PM UTC

rbanffy wrote: post #81

Tuna-Fish wrote: post #74

Earlier quoted context omitted.

Another tradeoff is size. You can pack about 4 raptors in the same area you can fit a single SSME. (Or, 8 in the space you can fit a single F-1). This is relevant because to lift the shuttle on 3 SSMEs, or the SLS on 4, they need to pack in massive amount of thrust in SRBs. Instead of doing that with all it's cost and safety implications, SpaceX intends to put 31 raptors on the bottom of their rocket. You could not f…

And, with 31 engines instead of 4, you get a massive increase in redundancy. If you lose one SLS SSME, you can push the others extra hard (they won't be reused anyway) and still make it to orbit (or land in the Atlantic). You'd need to lose 7 Raptors to be in the same bad position.

I wonder how nobody talks about ill fate of N-1 with 30 engines on the first stage with the idea that the number of engines was the reason for breakdowns.

Re: The Tech Behind SpaceX’s New Engine

#92

Post by ridgeguy » Wed, Feb 13, 2019, 9:29 PM UTC

prando wrote: post #24

https://www.netflix.com/title/80119093 My rocket-science knowledge is abysmal, but I thoroughly enjoyed this article and the Netflix documentary that I have linked to was incredible. Anyone even remotely interested in rockets should check it out :).

Excellent, thank you. There's a parallel between Sergei Korolev and Elon Musk, I believe.

Re: The Tech Behind SpaceX’s New Engine

#93

Post by avmich » Wed, Feb 13, 2019, 9:30 PM UTC

burfog wrote: post #71

Looking at the list of cycles on Wikipedia, I'm surprised that nobody seems to have used preburners to pressurize the tanks. Use a fuel-rich preburner to pressurize the fuel tank, and an oxygen-rich preburner to pressurize the oxygen tank. Mixing should be limited even if nothing special is done, due to the temperature and phase of matter and short timeframe. One could of course pay the weight penalty of a piston (ne…

> nobody seems to have used preburners to pressurize the tanks

IIRC, Block D taps some preburner exhaust for that...

Re: The Tech Behind SpaceX’s New Engine

#94

Post by ceejayoz » Wed, Feb 13, 2019, 9:32 PM UTC

avmich wrote: post #91

rbanffy wrote: post #81

Earlier quoted context omitted.

And, with 31 engines instead of 4, you get a massive increase in redundancy. If you lose one SLS SSME, you can push the others extra hard (they won't be reused anyway) and still make it to orbit (or land in the Atlantic). You'd need to lose 7 Raptors to be in the same bad position.

I wonder how nobody talks about ill fate of N-1 with 30 engines on the first stage with the idea that the number of engines was the reason for breakdowns.

The relevant tech - computer control, metallurgy, etc. - has come a ways since the mid 1960s.

SpaceX's lots-of-engines approach has been well proven on the Falcon 9 thus far.

Re: The Tech Behind SpaceX’s New Engine

#95

Post by [deleted] » Wed, Feb 13, 2019, 9:44 PM UTC

le-mark wrote: post #88

Nice article, but this part is a bit misleading: > American engineers went in the opposite direction. They believed that a fuel-rich mixture in the preburner was possible and could be done with existing metal alloys, so long as hydrogen was used as the fuel instead of kerosene. This ultimately lead to the development of the Space Shuttle Main Engine, which to date remains the most efficient liquid fuel rocket engine…

[deleted]

Re: The Tech Behind SpaceX’s New Engine

#96

Post by Agathos » Wed, Feb 13, 2019, 9:50 PM UTC

avmich wrote: post #87

Tuna-Fish wrote: post #72

Earlier quoted context omitted.

> But it adds the whole second gas generator and turbine. No, it doesn't lower part complexity as a whole :) . Because the fuel side and oxidizer side typically have a very different flow rates, many engines have separate pumps and turbines for them on separate shafts even if both sides use same fluids in the preburner. For example, see the SSME. With FFSC, each of the turbines have no sealing requirements. This mean…

> Because the fuel side and oxidizer side typically have a very different flow rates, many engines have separate pumps and turbines for them on separate shafts even if both sides use same fluids in the preburner. For example, see the SSME. By "many" you perhaps mean "many American". In Russian engines it's mostly a single shaft. > The main cost of doing it over gas generators (other than oxidation-resistant superallo…

> By "many" you perhaps mean "many American".

And by "many American," do you perhaps mean "pretty much just the Space Shuttle Main Engine?" Since that one, has America launched any new staged combustion engine off the ground?

Re: The Tech Behind SpaceX’s New Engine

#97

Post by btilly » Wed, Feb 13, 2019, 9:55 PM UTC

Hypx wrote: post #90

btilly wrote: post #69

Earlier quoted context omitted.

Well, sanity check. In 2017 the SLS launch was about 2 years out, but likely to slip: https://www.nasaspaceflight.com/2017/11/sls-managers-troops-... In 2019 the SLS launch is a bit under 2 years out, but likely to slip: https://arstechnica.com/science/2019/02/nasa-still-working-t... This strongly reminds me of the fact that late software projects are promised to be on time until about 6 weeks before launch, and then…

That's not quite correct. SLS is still slated to launch June of next year. It may get delayed to 2021 if problems are found. Also, Orion already flown in 2014, and will undergo an abort test in April.

You are right. After poking around for a bit, I found that SLS+Orion can launch without the upper stage. The upper stage allows more to be carried on the launch.

That said, I'm still on the side of betting with history. In most organizations, the deadline is the first date that nobody can (yet) disprove. When a deadline depends on problems not happening on this project that historically have been common, I think it is safe to bet that history will repeat itself.

This goes doubly for the SLS. Which is more ambitious than past launch systems, and is being built so long after the last new launch system was designed by the companies involved that there is little institutional knowledge left about how to do it. (Furthermore building with competing companies contracting for pieces that need to integrate just sounds like a recipe for expensive overruns to me.)

As opposed to the BFR. Which is being designed by a company with more recent experience of how to build new launch systems than the rest of the planet put together.

Re: The Tech Behind SpaceX’s New Engine

#98

Post by btilly » Wed, Feb 13, 2019, 9:57 PM UTC

carbocation wrote: post #89

btilly wrote: post #69

Earlier quoted context omitted.

Well, sanity check. In 2017 the SLS launch was about 2 years out, but likely to slip: https://www.nasaspaceflight.com/2017/11/sls-managers-troops-... In 2019 the SLS launch is a bit under 2 years out, but likely to slip: https://arstechnica.com/science/2019/02/nasa-still-working-t... This strongly reminds me of the fact that late software projects are promised to be on time until about 6 weeks before launch, and then…

Do you think this is a Lindy effect type of thing, or something different?

I wouldn't have drawn that comparison. But I wouldn't rule it out as a reasonable comparison without some data to point to.

Re: The Tech Behind SpaceX’s New Engine

#99

Post by Palptine » Wed, Feb 13, 2019, 9:59 PM UTC

le-mark wrote: post #88

Nice article, but this part is a bit misleading: > American engineers went in the opposite direction. They believed that a fuel-rich mixture in the preburner was possible and could be done with existing metal alloys, so long as hydrogen was used as the fuel instead of kerosene. This ultimately lead to the development of the Space Shuttle Main Engine, which to date remains the most efficient liquid fuel rocket engine…

Not true. Be-4 is a staged combustion metholox engine.

Re: The Tech Behind SpaceX’s New Engine

#100

Post by avmich » Wed, Feb 13, 2019, 10:01 PM UTC

Agathos wrote: post #96

avmich wrote: post #87

Earlier quoted context omitted.

> Because the fuel side and oxidizer side typically have a very different flow rates, many engines have separate pumps and turbines for them on separate shafts even if both sides use same fluids in the preburner. For example, see the SSME. By "many" you perhaps mean "many American". In Russian engines it's mostly a single shaft. > The main cost of doing it over gas generators (other than oxidation-resistant superallo…

> By "many" you perhaps mean "many American". And by "many American," do you perhaps mean "pretty much just the Space Shuttle Main Engine?" Since that one, has America launched any new staged combustion engine off the ground?

I believe GP meant that not for closed cycle engines, but for all turbo-pump driven engines, which in USA mostly means open loop (gas generator) engines. In USA the tradition was to add complexity in form of gears and extra axes to get pumps running with more optimal speed, while in Russia (USSR) it was to reduce efficiency and gain in simplicity, robustness and mass.