In article ,
David Higgins wrote:
Anyone have any thoughts on how hard it would be to air-start an SSME?
They seem to be proposing using one (or two) on the second stage.

There's nothing inherently hard about it. It does require some added
equipment, either on the SSME stage or on the previous stage, to do
various minor pre-start jobs that are done for the shuttle by ground
support gear. My understanding is that this was studied quite a while
back -- there have long been proposals to use SSMEs as high-performance
space maneuvering engines, for example -- and it doesn't look difficult.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |