johnhare wrote:

The 460 seconds clearly was a vacuum Isp he was refering to. If it had
been 360 vs 320 seconds, then it would have been sea level performance.
Starting at sea level, you do need the high pressures to get performance,
which is your point. Out of context, I'm not sure what performance hit
was being refered to if not just the vacuum Isp.

Was the engine also intended to operate at sea level? In that case,
dropping the chamber pressure would also force the expansion ratio to
be reduced, which would affect vacuum Isp.

Paul
who wonder why they aren't using any of those
nozzle tricks that would get around this