AndyMc - 26/11/2005 9:20 AMSource: http://www.usspacenews.com/index.htmlThe CEV Heavy Lift Launch Vehicle (HLV) upper stage engine will be an updated version of the J-2 (a J-2S to be exact) from the Apollo program. Rocketdyne has about 9 J-2's developed for Apollo in engineering storage in California and excellent condition. These would be used as starting points for the J-2S.I wonder what other delights they have tucked away in their basement - an F1 or two perhaps
AndyMc - 26/11/2005 4:58 PMI think they mean 'The Big One' SDHLV. The upper stage is to have two of them, last time I checked. Single SSME is for the upper stage of 'The Stick'
Spacely - 27/11/2005 7:20 PMThe SSMEs are a fairly amazing model of consistency considering their piecemeal design, testing, etc. If history ultimately remembers the STS kindly, the genius of the SSMEs will be a primary cause.
CuddlyRocket - 28/11/2005 8:47 AMThere has been 30+ years of manufacturing methodology improvements since the J-2 was last used, which should have an impact on their reliability. But yes, I would expect them to take into account the SSMEs reliability, but this may be a question of cost v reliability.
HailColumbia - 28/11/2005 7:59 PMwhat exactly does the "S" signify?
HailColumbia - 28/11/2005 11:09 PMwell what about the J-2S? its not as if the J-2 was reusable.
AndyMc - 29/11/2005 8:10 AMReading from Astronautix and elsewhere, the J-2S engine operates at lower a chamber pressure of 30 bar as opposed to 204 bar for the SSME, and has a low thrust feature "for propellant tank settling, on-orbit maneuvering, and rapid engine chill down prior to firing."Two J-2S engines give the same thrust as one SSME (2x116 kgf - J-2s / 232 kgf - SSME), plus this offers a back-up should one fail. Is one J-2S engine powerful enough to complete the TLI burn though?Astronautix has the ISP for the J-2S as being 426s as opposed to 453s for the SSME, though elsewhere http://yarchive.net/space/shuttle/j2s.html this guy states that the J-2S ISP is 455s. This may be possible, as a couple of other engines the HG-3 & HG-3-SL derived from the J2 achieved a higher ISP (452s) and higher thrust (142 kgf) using a high pressure combustion chamber.http://www.astronautix.com/engines/hg3.htmhttp://www.astronautix.com/engines/hg3sl.htmSo maybe the J2 and its derivatives still have some potential for development by feeding back knowledge gained from building and operating SSMEs over the last 25 years.