[AR] Re: clusters and reliability (was Re: Re: 3 no 4 no 5 legs.)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 22 Jan 2016 19:23:27 -0500 (EST)
On Fri, 22 Jan 2016, Hugh Blair-Smith wrote:
I attended the Apollo 6 launch and understood at the time that only one
S2 engine failed (because of too much trauma from pogo oscillations of
the first stage), and that IBM's fault response logic erroneously shut
down the wrong engine...
That may have been what they thought at first glance, but no, it's not
what emerged from the detailed analysis. The Apollo 6 Flight Evaluation
Report (well, most of it, the last few chapters are missing) can be found
at <
http://klabs.org/history/history_docs/jsc_t/apollo_06_saturn_v.pdf> if
you want to read the details, down to the plug and receptacle numbers of
the misconnected LOX-prevalve wiring. :-) The interesting bit starts
around page 127 (aka page 6-11).
Although it was tempting to think that the first-stage Pogo oscillations
might have caused Apollo 6's other problems (igniter fuel-line failures in
second and third stages, plus a skin failure on the spacecraft adapter),
my understanding is that the fuel-line failure was replicated in ground
test without any attempt to simulate the Pogo effects, and the final
conclusion was that the appearance of the various problems on the same
flight was largely coincidence.
The problem with the S4B was not really an engine problem, just the fact
that it had to do a considerable fraction of the S2's job to reach
orbit, and then wasn't able to restart on orbit to do the test version
of the TLI burn.
The restart failure most definitely *was* an engine problem. Yes, the
S-IVB achieved orbit, making up for the S-II performance shortfall. But
the engine's igniter fuel line broke (in the same way that S-II engine
#2's did) about a minute before the end of the burn, although the
resulting engine damage didn't progress rapidly enough to prevent orbit
insertion. Same report, starting around page 160 (aka 7-8), shows the
small but noticeable drops in thrust and Isp late in the burn, and later
discusses various temperature anomalies nearby, starting around the same
time (including an apparent flash fire at one point!).
Had the engine managed to restart, it would probably have died (the same
way S-II #2 did) during the second burn. However, the lack of fuel flow
to the igniter made restart ignition impossible, and the control system
shut the engine down when it didn't light.
MIT's Apollo Guidance Computer had to emulate that burn by commanding a
Service Propulsion System burn, then get back on its nominal timeline,
commanding a "power dive" by the SPS to achieve entry at close to
return-from-Moon speed. We thus recovered most of the day's objectives
and would have celebrated handsomely if that creep hadn't shot Martin
Luther King Jr. the same day.
Yes, the improvised SPS burn pretty much saved the spacecraft side of the
mission. I'm sure the spacecraft guys would have celebrated handsomely,
but the launcher guys weren't so happy. :-)
Henry
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