"richard schumacher" wrote in message
...
A potential problem with single-impulse separation methods such as
springs arises if the first stage continues to generate thrust, because
it can then catch up with the second stage. This is exactly what
happened with the 3rd Falcon 1 flight.

On another discussion forum, Henry Spencer said this is almost exactly what
nearly happened during Apollo 15's S-IC separation, so naturally I went
digging for details.

http://history.nasa.gov/alsj/a15/a15mrp6.pdf

Quote from above:

Four of the eight S-IC retromotors and all of the S-II stage
ullage motors were removed for this flight; therefore, the
S-IC/S-II separation sequence was revised. This sequence change
extended the coast period between S-IC outboard engine cutoff
and S-II engine start command by one second. The S-IC/S-II
separation sequence and S-II engine thrust buildup performance
was satisfactory.

From what I understand, the above deleted motors were added back for
subsequent flights, but I can't find a PDF online to confirm this.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein