Jeff Foust has an overview at The Space Review today about a new concept that many (including many in the astronaut office) are pushing as a CEV delivery vehicle–an SRB-based design, with a new J-2 powered upper stage. This is what many are calling a “single-stick” vehicle, as opposed to the EELVs with their strap-on boosters.

I actually agree that such a system could be built, and could have a (marginal) cost of a hundred million per flight (though it’s not clear what the actual cost per flight would be, including amortization of the development costs). However, the issues aren’t quite as simple as the proponents make out.

A major drawback of using an EELV to launch the CEV is that neither the Atlas 5 nor the Delta 4 are