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The Tech Behind SpaceX’s New Engine

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Re: The Tech Behind SpaceX’s New Engine

#101

Post by itp »

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…

The article does not claim that the SSME is full flow; as described in the quote you pulled, it's fuel-rich.

BE-4 is not full flow, but oxidizer-rich (https://en.wikipedia.org/wiki/Staged_combustion_cycle#Oxidiz...).

Re: The Tech Behind SpaceX’s New Engine

#102

Post by itp »

Palptine wrote: post #99
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.

Be careful with terminology. BE-4 and Raptor are both staged combustion methalox engines. Raptor is full-flow staged combustion, while BE-4 is oxidizer-rich staged combustion.

Re: The Tech Behind SpaceX’s New Engine

#103

Post by CarVac »

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.

Apparently the N-1 never actually fired all 30 engines simultaneously before launch, so there was no way to detect plumbing issues.

Additionally, their control scheme was designed to shut down the engine opposite to any failed engine, meaning that they had very little engine-out margin in the inevitability of an engine failure.

All in all, we can (and have, with the Falcon Heavy) do much better.

Re: The Tech Behind SpaceX’s New Engine

#104

Post by Obi_Juan_Kenobi »

burfog wrote: post #76
JumpCrisscross wrote: post #75

Earlier quoted context omitted.

> I'm surprised that nobody seems to have used preburners to pressurize the tanks This combines the worst of both worlds. You get the weight and complexity of turbopumps. And you get the weight, explosion risk and leakiness of pressure vessels.

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…

I think you're underestimating the pressures involved here by several orders of magnitude.

To drive the flow of fuel and oxidizer into the combustion chamber, you must overcome the pressure inside. To drive this flow, the turbopump output pressure will be of comparable magnitude to the combustion chamber. This pressure is in the realm of a few 10s of megapascals, or a few thousand PSI. This is a hard design requirement.

If you're proposing to "skip the turbopump", then necessarily you'd have to pressurize the entire fuel and oxidizer tanks to these high pressures. This is, to put it very mildly, utterly infeasible.

Re: The Tech Behind SpaceX’s New Engine

#105

Post by avmich »

ceejayoz wrote: post #94
avmich wrote: post #91

Earlier quoted context omitted.

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.

That's fine, but it means you can't blame the sheer number of engines on N-1 to its poor performance. There is no law which forbids launching, e.g. Soyuz with 32 working from the start chambers, or Energiya with 20 chambers, or Falcon Heavy with 27 chambers successfully. It's other reasons - maybe computer control (KORD was a complex system to create), maybe metallurgy (even though NK-33, manufactured in ~1973, manage to fly after 40+ years in storage), maybe something else.

This is just to compare optimism for heavily multi-engined BFR with suggestions that N-1 was doomed just because of the number of engines.

Re: The Tech Behind SpaceX’s New Engine

#106

Post by newnewpdro »

JumpCrisscross wrote: post #20

“Benefits of the full-flow staged combustion cycle include turbines that run cooler and at lower pressure, due to increased mass flow, leading to a longer engine life and higher reliability.” TL; DR Full flow lowers turbine temperatures at the expense of parts complexity. Given turbopumps are the devil’s ass part of rocketry, this has been a sought-after technology. The pay-off isn’t so much efficiency as much as lon…

I'm confused; wouldn't the oxidizer-rich half run hotter? Isn't that challenge the Russians overcame but the US punted on back in the days of the space shuttle?

Your post and the referenced wikipedia article claims the turbines run cooler. Wouldn't that only be true for the fuel-rich side?

Re: The Tech Behind SpaceX’s New Engine

#107

Post by avmich »

CarVac wrote: post #103
avmich wrote: post #91

Earlier quoted context omitted.

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.

Apparently the N-1 never actually fired all 30 engines simultaneously before launch, so there was no way to detect plumbing issues. Additionally, their control scheme was designed to shut down the engine opposite to any failed engine, meaning that they had very little engine-out margin in the inevitability of an engine failure. All in all, we can (and have, with the Falcon Heavy) do much better.

> meaning that they had very little engine-out margin

N-1 could complete the mission with up to 4 engines turned off from the start. And I guess it it's not from the start, you could turn off even more engines and still have a successful flight.

Even though Saturn-V is heavier, N-1 has more lift-off thrust. Partially to have this kind of redundancy.

Re: The Tech Behind SpaceX’s New Engine

#108

Post by Tuna-Fish »

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.

N-1 steered by differential thrust, meaning every engine points directly backwards and losing one on the rim means you have to turn off another on the opposite side to compensate, and now you've lost all the margin there is in the design and quite a lot of control authority too. All SpaceX rockets steer by gimbaling engines, meaning you lose one on the rim and you just adjust the thrust vectors to compensate.

Re: The Tech Behind SpaceX’s New Engine

#109

Post by Agathos »

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.

As I recall, nobody could stop talking about it in the weeks before the Falcon Heavy demo.

Re: The Tech Behind SpaceX’s New Engine

#110

Post by buboard »

ballooney wrote: post #83
CarVac wrote: post #9

Earlier quoted context omitted.

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.

does the mass of the exhaust fuels count as well? whats the percentage of thrust being lost in a gas generator?
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