Falcon 1 Staging Recontact - Engine Burp

Jeff Findley wrote:
"Pat Flannery" wrote in message
telephone...

Jeff Findley wrote:

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.


No, they stayed off on all Apollo J-series flights IIRC (15, 16, 17).


Actually, the PDF's that Jorge found (see his recent post in this thread)
clearly state that they went back to eight retromotors for the S-1C stage on
Apollo 16 and Apollo 17 (twice the number on Apollo 15).

Perhaps the ullage motors on the S-II stage weren't added back for 16 and
17?


S-II shouldn't need any ullage motors as such...separation of the rear
interstage occurs while it's under power, and S-II only makes a single
burn during ascent. The closest thing to ullage engines on S-II proper
were the four 4 (originally 8) motors on the interstage, and all of
those were removed for the J-Series launches:
http://www.hq.nasa.gov/pao/History/S...ages/m406b.jpg

Still, it's clear there was a bit of tweaking going on with the Saturn V to
eek out a bit more performance on later flights. The other point I wanted
to make was that even von Braun's team cut back too far at times, as was the
case with the S-1C retromotors.


By that point the rocket and what was done with mods to it was probably
out of von Braun's hands.
When they originally built it they took a very conservative approach to
things, which is why it had the 8 separation/ullage motors on the
interstage, even though they expected four would be sufficient.
This does raise a interesting question though - with all eight removed
from the interstage, how were the propellants kept seated during
staging? As the S-IC shut down and separated, the S-II was in free-fall
and still subject to some air drag.
Did the pre-start cycle on its J-2s generate enough thrust to keep the
propellants at the back of the tanks?
There are a ton of nifty Saturn I and Saturn V photos and drawings here
BTW: http://history.nasa.gov/MHR-5/contents.htm

Pat

On Fri, 08 Aug 2008 03:29:09 GMT, in a place far, far away,
(Derek Lyons) made the phosphor on my monitor glow
in such a way as to indicate that:

richard schumacher wrote:

Barring some assembly error the odds of success for the 4th
Falcon 1 flight should be pretty good.

That's what everyone said after the first.

And the second too.

"Everyone"?

Not I.