Chair Force Engineer

Wednesday, January 21, 2009

A Reprieve for SSME?

Rob Coppinger suggests that the days of the Space Shuttle Main Engine may not be over when the shuttle system is retired in 2010. When the shuttle program ends, there will be a number of engines that have not exceeded their lifetimes. It’s conceivable that a commercial rocket could use them on a single-use basis, although it’s unlikely that anybody would want to sink millions of dollars into developing a rocket if the supply of engines is finite.

Another (remote) possibility is that the SSME’s may find their way back onto the Ares V, as per the original ESAS studies of Summer 2005. The thought of recovering the SSME’s in a fashion similar to that proposed for the Atlas V engines had occurred to me. It’s harder to pull off a recovery of this nature on a cluster of six SSME’s, but it’s certainly worthy of study. It would improve Ares V’s performance to orbit (SSME has higher specific impulse than the RS-68,) but the thrust levels would drop off. The change to a six-engine cluster (versus the five engines on the original Ares V) might help offset that. Conversely, it might allow a switch back to the shuttle-derived 8.4-meter tankage instead of the all-new 10 meter tankage of the current design, and avoid the expense of changing the spacing between the SRB cut-outs on the Mobile Launch Platforms.

On a related note, NASA is looking at other uses of Ares V, especially for science missions. I must admit that the prospect of a massive space telescope, used to spot earth-like worlds around distant stars in our galaxy, is too exciting to ignore. At the same time, it's not realistic to think that Ares science missions will appreciably increase the Ares launch rate and amortize the big booster's massive standing army costs. Big-budget science missions on the scale of Hubble Space Telescope only launch once every few years. The obvious way to double the Ares launch rate is to dump both Ares I and Ares V in favor of two launches of an intermediate-capability rocket. You know, something that looks kinda like Jupiter-232. Or you can further amortize the existing standing army costs for the existing Delta or Atlas rockets by using six EELV's or so per lunar mission. The point is that the inherent fiscal inefficiencies of the Ares system will not be fixed through the addition of an occasional science mission to the manifest. Only a marked reduction in fixed costs or a steep increase in flight rate will make the system more efficient.