SSME Efficiency Upgrade

[fredinno]

Would it be possible to upgrade the SSME in the near future to be even more efficient than it is now?

[Bill Phil]

Maybe if you increase the exhaust ratio. But that would be pretty expensive and the gains might not be enough to justify it.

[Guest]

I think the most you could do would be to change the nozzle to alter performance at different altitudes, but other than that I'm pretty sure it's as good as it's going to get. Changing the cycle would make it an entirely different engine and may not even help.

[PB666]

Would it be possible to upgrade the SSME in the near future to be even more efficient than it is now?

The SSME has an ISP of 452.3 seconds, and the limit is shy of 500 so right now its 91% is ISP at sea level is 366. These values are far higher than any comparable

LFOx engine in KSP. If you want to get a higher ISP you would have to add nuclear assist. The problem with the shuttle is not its engines, its the shuttle itself. For flights that don't require a 7 person crew, its a huge waste of payload weight. However it could be repurposed with a smaller crew and larger payload bay for carrying more stuff into space.

Anyway the shuttle program is over, finished.

[UmbralRaptor]

I wouldn't be surprised if a redesigned nozzle could get you 10-20 s higher vacuum Isp. That would probably cut into the TWR and sea-level Isp, though. I'd rather look towards ways to make it cheaper and at most add the ability to air-start (if possible).

[YNM]

Thought they're fitting it for the core stage of SLS ? Maybe they need to increase the thrust and make it cheaper and lighter. Making the atmospheric ISP higher should also works.

[fredinno]

The SSME has an ISP of 452.3 seconds, and the limit is shy of 500 so right now its 91% is ISP at sea level is 366. These values are far higher than any comparable

LFOx engine in KSP. If you want to get a higher ISP you would have to add nuclear assist. The problem with the shuttle is not its engines, its the shuttle itself. For flights that don't require a 7 person crew, its a huge waste of payload weight. However it could be repurposed with a smaller crew and larger payload bay for carrying more stuff into space.

Anyway the shuttle program is over, finished.

SSMEs are used in the SLS, so they're still going to be used. Either way, I (think) I found a way to make the SSMEs even more efficient using plug nozzles. How difficult would it be to integrate them into the SLS, and would it be economical to add them in a SSME-f upgrade, and would it be worth it?

[YNM]

They're gonna be dumped though, so better to make them cheaper. Plug nozzle suffers from relatively higher cost to build, no ?

[Nibb31]

The SSME is now called RS-25. The existing ones have been refurbished to remove the regenerative cooling nozzles and other reusability features. Then they will be thrown away on the SLS. If there are more than 3 SLS launches, Aerojet Rocketdyne will have to build new ones.

They are pretty efficient engines. I'm not sure what you would achieve by improving their efficiency. As with most aspects of engineering, the laws of diminishing returns apply here. A poorly optimized designed only requires a small effort to make a spectacular improvement. A highly optimized designed (like the RS-25) requires a huge effort for litte improvement. Effort is money, so it's not worth it.

[shynung]

Typical RS-25s burn hydrogen-oxygen propellant. Replace the oxygen with fluorine, up goes your specific impulse.

Sure, you'll have to deal with the stream of HF going out your nozzle afterwards. But, by replacing the aluminium in the SRBs fired alongside (which typically burn aluminium-ammonium perchlorate) with beryllium, the HF and BeO (along with chlorine leftovers) react into BeF2 and HCl, which is less dangerous, in addition to giving a boost to SRB specific impulse.

Yes, this is all stupidly dangerous (and expensive) stuff that even the DoD probably wouldn't even bother. But the performance gains are there.