Ian Woollard wrote:

Michael Walsh wrote in message ...
The only virtue that a SSTO has over a TSTO (two stage to orbit) reusable
vehicle is the reduction in cost by developing and using only one vehicle
instead of two. If the SSTO does not show a cost advantage then there
is no reason to build one.

That's not necessarily the case, there may very well be reliability
advantages of SSTO, due to system simplicity.

I have made the implied assumption that safety should not be
compromised.

I should not have made the mistake of using the term "only virtue" but
there is still no reason to build a SSTO unless it shows a cost advantage.

In addition, SSTO does not have the strong tendency of TSTO to drop
stages onto occupied land that can preclude many orbits.

If we are talking about fully recoverable systems then I would expect a
the recovery to take place in a controlled location, even if it was not
a "flyback" system.

For example Soyuz would have been unable to reach Columbia's orbit due
to these constraints- (however, overflying the land would still entail
some risk, but it might well be considered acceptable on a rescue
mission.)

The Russians continually launch over land areas and the Soyuz reaches the
ISS on a regular basis. I am not sure what the flight path would have been
for a Columbia rescue mission. That is somewhat of a special case.

Mike Walsh