Bill Weronko; What I'd like to know is what is the status of the advanced RL-10, the RL-60 program. There are NASA documents as recent as this year that discuss a MB-60 rocket engine development program, with the same listed purpose and general specifications as the RL-60. It was announced by JAXA and NASA a joint development design by Boeing and Mitsubishi Heavy Industries (MHI) under the technical management of NASA Marshall Space Flight. There is another NASA documents that refer a advanced upper stage named MARC-60 that sounds a great deal like the RL-60 program. It is a joint program between MHI and Aerojet Rocketdyne. These may be the same program. I have not seen a funding line item in the NASA budget for either.
Grey Buckleton; Pretty sure the RL60 was canceled but near completion. The airforce will ask for it only when all the old RL10's get used up. JAXA seems to be putting its development cash in to a new expander cycle 1st stage engine. RL60 would be great on SLS and Atlas.
Greg Beat; Bill - The RL-60 program was in the home stretch (2003), and then shelved. http://en.m.wikipedia.org/wiki/RL60 IF NASA had put their $$$ to complete the RL-60/MB-60 program, instead of the J-2X ($1 billion USD), we would have had the engine by now. --- The only positive from J-2X program, was the new Engine Controllers which will be used as the Main Engine Controllers (MEC) for the RS-25 engines on SLS. --- We will eventually see this engine, as fabrication costs for the RL-10 design (1960s) are no longer competitive. In fact, it is now the expensive production engine for the thrust achieved.