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"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 e
by cromwellian 12y ago
"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.
- swatkat 12y agoNK-33 is RP/LOX, whereas SSME is LH2/LOX. LH2/LOX cryogenic engines have higher Isp compared to other solid and liquid engines. ISRO's CE-7.5 LH2/LOX engine[1] has an Isp of 454s. [1] http://en.wikipedia.org/wiki/CE-7.5 http://en.wikipedia.org/wiki/CE-7.5
- justin66 12y agoWas anything about cromwellian's statement inaccurate, such that it should have been downvoted? I'm pretty sure I understand everything being discussed here but I don't understand THAT.
- marktangotango 12y agoI didn't down vote it, but the difference between RP1 and Liquid Hydrogen engine performance is WELL known. Thus his assertion that SSME's are better, although true as comparison of rocket engines in general, is false when comparing LOX/RP1 engines specifically (since the SSME are NOT LOX/RP1), which the grandparent was clearly doing. Similarly, citing the 850 ISP of the experimental NERVA engines is equally out of context.
- cromwellian 12y agoI didn't see the LOX/RP1 qualifier when I replied (I was responding to the quoted sentence). 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.
- termain 12y agoYes, the RS-25/SSMEs aren't "easily the most efficient rocket engines ever built". As noted below, there's NERVA.
- pavel_lishin 12y agoAnd yesterday's launch illustrates why people are kind of nervous about using them as a way to take off from the planet's surface.
- cromwellian 12y agoBut much lower thrust.
- jpetrik 12y agoshuttle used hydrolox, antares uses kerolox, hardly comparable. hydrolox engines have vastly superior Isp but come with their own set of limitations.
- gedmark 12y agoI should have been clear on the propellant - the SSME is a hydrogen engine. For a lot of reasons, comparing engines of different propellants by using a single performance number alone doesn't make a lot of sense. But if you want to talk about hydrogen engines, the Russians built the RD-0120, which reportedly had a higher Isp and chamber pressure than the SSME... http://en.wikipedia.org/wiki/RD-0120 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.