Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The Tech Behind SpaceX’s New Engine

hackaday.com

Post reply on HN
Print view View original

81–90 of 137 posts

Re: The Tech Behind SpaceX’s New Engine

#81

Post by rbanffy »

Tuna-Fish wrote: post #74
zackmorris wrote: post #67

Earlier quoted context omitted.

To put this in perspective, the F-1 engine of the Saturn V (one of the biggest rocket engines ever made) only put out about 3.5 times more thrust (6.7 MN or 1.5 Mlbf) than the Raptor (1.9 MN or 0.43 Mlbf). Also some people might not realize how much liquid is being pumped by rocket engines (the Saturn V F-1 could drain a 30,000 gallon swimming pool in 10 seconds): Each second, a single F-1 burned 5,683 pounds (2,578…

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.

Re: The Tech Behind SpaceX’s New Engine

#83

Post by ballooney »

CarVac wrote: post #9
kumarvvr wrote: post #6

This is an excellent article. Just curious, how much more efficient is the full-flow engine? And, what exactly is the deal with the seals the article is talking about? Anyone have more info?

A full-flow staged combustion engine has more efficiency due to both propellants being fully vaporized before they mix, rather than a liquid-liquid mixture (as in a gas generator engine) or a liquid-gas mixture (as in a normal staged combustion engine). The seals are between the turbine side (hot gas) and compressor side (liquid fuel) of the turbopump. In a full-flow staged combustion engine, you don't have to worry…

No, this is all just wrong. The efficiency is because you dont throw a load of enthalpy overboard as in a gas generator. The phase is _exremely_ second order by comparison.

You’re all over this thread being wrong and confused.

Source: am a rocket engine designer.

Re: The Tech Behind SpaceX’s New Engine

#84

Post by erikpukinskis »

Tuna-Fish wrote: post #72
avmich wrote: post #61

Earlier quoted context omitted.

> ...it also lowers part complexity, because it eliminates interpropellant seals. But it adds the whole second gas generator and turbine. No, it doesn't lower part complexity as a whole :) . > It improves achievable chamber pressure Yes, I'd even argue that's the penultimate goal of full-flow scheme. 1) For a rocket engine you usually (almost always) want as high Isp (which is approximately the speed of gasses flowin…

> 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…

Was curious about your mention of Stennis, so I looked it up:

https://en.wikipedia.org/wiki/John_C._Stennis_Space_Center#E...

Sounds like SpaceX has, with NASA and the State of Mississippi modified the test stand to support methane.

Re: The Tech Behind SpaceX’s New Engine

#85

Post by SECProto »

Symmetry wrote: post #77
SECProto wrote: post #70

Earlier quoted context omitted.

> Also, having both inputs already be gasses mean they mix better. This will have a tiny benefit in them burning more completely. But more importantly they'll burn better across a wider range of thrusts, which could be important for throttling down the engine for landing. Also, and importantly for the design of the engine, it's much much easier* to computationally model the mixing of two gases, to ensure complete mix…

Have you seen SpaceX's talk at some NVidia conference about their homegrown Computational Fluid Dynamics simulator? It was really interesting. https://www.nextplatform.com/2015/03/27/rockets-shake-and-ra...

I hadnt seen that exact article, but i recall reading (or listening to a lecture) that mentions how one advantage of methane is the possibility to use CFD in design, while that was still outside the realm of possibility with RP-1 due to complexity of reactants (differing phases and many compounds)

Re: The Tech Behind SpaceX’s New Engine

#86

Post by ballooney »

rbanffy wrote: post #80
burfog wrote: post #76

Earlier quoted context omitted.

Skip the turbopump. That is the whole point of pressurizing. Pressurizing has weight advantages. You can use a balloon tank. The tank no longer has to have the rigidity to support itself. Rockets with typical cycles have used balloon tanks. Even modern ones like the Falcon 9 are partially that way, with just enough rigidity to be erected empty on the pad. The Falcon 9 uses helium to pressurize; that could be changed…

This is one of the reasons SpaceX uses supercooled fuel and oxydizer (and one of the reasons for going methalox in the first place) - the tanks self-pressurize, so they can skip the Helium system. Pumps are still good because you really don't want the tanks to pressurize at the same pressure as the combustion chamber. If you do, you'll see a rapid disassembly, but your claim on it being unscheduled will be questioned…

This is completely, completely wrong. Really honestly confused nonesense. Supercooling lowers the ullage pressure, if anything increasing the need to pressurise (self or otherwise), because the self pressurisiation (the vapour pressure) is lower. So you have to do additional work to feed the pumps. The only reason to supercool is to increase the density. Your comment is quite incorrect.

Re: The Tech Behind SpaceX’s New Engine

#87

Post by avmich »

Tuna-Fish wrote: post #72
avmich wrote: post #61

Earlier quoted context omitted.

> ...it also lowers part complexity, because it eliminates interpropellant seals. But it adds the whole second gas generator and turbine. No, it doesn't lower part complexity as a whole :) . > It improves achievable chamber pressure Yes, I'd even argue that's the penultimate goal of full-flow scheme. 1) For a rocket engine you usually (almost always) want as high Isp (which is approximately the speed of gasses flowin…

> 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 superalloys...) is that all parts of the engine sort of circularly depend on each other...

Yes, rocket engine is usually a complex dynamic system, with deep feedback loops. You can still get gas generator and turbines with pumps tested separately, but you need to measure dynamic properties - like resonance frequencies - in order to have better chances of the good work when the system is integrated.

Re: The Tech Behind SpaceX’s New Engine

#88

Post by le-mark »

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 ever flown.

SSME performance was due to H2 vs kerosene, it was not a full flow engine.

Edit; also no mention of Blue Origins BE-4 which is also a full flow engine.

Re: The Tech Behind SpaceX’s New Engine

#89

Post by carbocation »

btilly wrote: post #69
Rebelgecko wrote: post #51

Earlier quoted context omitted.

I would bet money that SLS+Orion launches before Falcon Super Heavy+Starship. It looks like SLS is already doing integration testing for the various cores and starting to assemble the main components. I'd guess 2021 at the latest, as long as there's no multi-month government shutdowns in the meantime.

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?

Re: The Tech Behind SpaceX’s New Engine

#90

Post by Hypx »

btilly wrote: post #69
Rebelgecko wrote: post #51

Earlier quoted context omitted.

I would bet money that SLS+Orion launches before Falcon Super Heavy+Starship. It looks like SLS is already doing integration testing for the various cores and starting to assemble the main components. I'd guess 2021 at the latest, as long as there's no multi-month government shutdowns in the meantime.

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.
Post reply on HN