Hydrolox Engines

[JoeFromRIUSA]

What operational hydrolox engine has 1) the highest specific impulse and 2) the highest thrust?

[Ixokani]

https://en.wikipedia.org/wiki/Comparison_of_orbital_rocket_engines

ISP: RD-0146D @ 470s
Thrust: RS-68A @ 3135kN

To the extent that list has accurate numbers, naturally.

[spacenut]

Maybe someone will chime in.  I think the highest thrust for and existing engine is the RS-65 on Delta IV.  Don't know about specific impulse unless it is an RL-10 used on the Centaur upper stage on Atlas V, and on the new Vulcan.  Blue Origin is working on the BE-7. 

Russia has some, but don't know much about them.

Largest ever design was the M1 in the 1960's that was to be used on the Nova Rocket.  Components were tested but engine never built.  It was to have 1.5 million lbs thrust, same as the F-1 used on the Saturn V.   

[deltaV]

I think the highest thrust for and existing engine is the RS-65 on Delta IV.

You mean RS-68A. AFAICT there is no RS-65 engine.

[whoopigoldberg]

What operational hydrolox engine has 1) the highest specific impulse and 2) the highest thrust?

With a particular impulse of roughly 452 seconds, the Space Shuttle Main Engine (SSME) is the hydrolox engine in operation that has the highest specific impulse.

With a thrust output of about 300 kN (67,000 lbf), the Ariane 5 ES Vulcain 2 engine is the operational hydrolox engine with the highest thrust.

[deltaV]

With a particular impulse of roughly 452 seconds, the Space Shuttle Main Engine (SSME) is the hydrolox engine in operation that has the highest specific impulse.

No, that's not the highest specific impulse hydrolox engine. Several RL 10 variants are better.

[Spiceman]

RL-10B-2 : 466.5 seconds.  And back in the late 1970's NASA tested a small hydrolox engine at component level, with a theoretical isp of 476 seconds. Seems to be the absolute maximum.

[deltaV]

Also OP don't focus on specific impulse alone. Dry mass, as measured by thrust-to-weight ratio, is also very important. An engine optimized solely for specific impulse would be useless because it would have infinite dry mass because of an infinitely large nozzle among other reasons.

[Spiceman]

478 seconds theoretical, 476 once assembled (or close). Was for the Shuttle Space Tug, rebranded OTV in the 1980's.

https://www.google.fr/books/edition/Space_Shuttle_1979/MokEaHhvpgsC?hl=fr&gbpv=1&dq="specific+impulse""478+seconds"&pg=PA571&printsec=frontcover

https://www.google.fr/books/edition/1980_NASA_authorization/NDXRAAAAMAAJ?hl=fr&gbpv=1&dq="specific+impulse""476+seconds"&pg=RA1-PA2114&printsec=frontcover

[Skye]

Highest I_sp in operation right now: RL10-B-2 @ 466.5s Vac (doesn’t operate ASL)

Highest thrust in operation right now: RS-25 @ 1,860 kN ASL, 2,279 Vac

Highest I_sp ever: РД-0146D @ 470s Vac (didn’t operate ASL)

Highest thrust ever: RS-68A @ 3,137 kN ASL, 3,560 kN Vac

Hope this helps! 

[Skye]

What operational hydrolox engine has 1) the highest specific impulse and 2) the highest thrust?

With a particular impulse of roughly 452 seconds, the Space Shuttle Main Engine (SSME) is the hydrolox engine in operation that has the highest specific impulse.

With a thrust output of about 300 kN (67,000 lbf), the Ariane 5 ES Vulcain 2.1 engine is the operational hydrolox engine with the highest thrust.

Bold mine

SSME has ~6x the thrust of Vulcain 2.1?

And RL10-B-2 has highest Isp at 466.5s