"The US has still yet to build anything matching its performance"
The Space Shuttle Main Engines had an Isp of 452s and 500,000 lb of thrust, easily the most efficient rocket engines ever built.
The Space Shuttle Main Engines had an Isp of 452s and 500,000 lb of thrust, easily the most efficient rocket engines ever built.
http://en.wikipedia.org/wiki/RD-0120
Although I don't believe we ever tested it on our own test stands, so it's impossible to know for sure.
By the way you are conflating vacuum Isp with sea level Isp (what I was using). The Sea level Isp of the SSME is 366 s.
The SSME is also a fuel-rich staged combustion cycle. The point I was making above is that the Russians were able to get an ox-rich staged combustion cycle working reliably. That's the key technology breakthrough that we have never duplicated.
ISRO's CE-7.5 LH2/LOX engine[1] has an Isp of 454s.
Similarly, citing the 850 ISP of the experimental NERVA engines is equally out of context.
Let me qualify the SSME claim as "highest Isp/Thrust of any widely used engine". Prototypes or engines that haven't flown much IMHO aren't able to make this claim.
The NK-33 may beat a Merlin 1D, but what much do they cost to make and what is the reliability? If you make 100 NK-33s and 100 Merlin 1Ds, what's your total budget, and how many NK-33s will fail compared to the Merlin 1D?
One thing I get with SpaceX, is that their engines are not designed to push the performance envelope. They want them to be cheap and reliable.
hydrolox engines have vastly superior Isp but come with their own set of limitations.