On Sun, 6 Oct 2013, Henry Vanderbilt wrote:
...the 2nd-stage restart attempt resulting in a hard start bad enough to
disable the engine and scatter some debris, but not bad enough to
rupture the stage tanks or feed lines.
Hmm, yes, a very interesting possibility. A hard start can be violent
enough to do damage, e.g. by the acceleration transient, without actually
*bursting* anything. (Gemini 6's Agena target was lost due to a hard
start that damaged control electronics.)
Speculative, of course, but it is worth noting that while they've
acknowledged a restart problem, they've said nothing about its nature
yet. It was FWIW apparently bad enough to immediately rule out a retry,
given that remaining propellants were vented right afterward.
If (dim) memory serves, there is at least one expendable item (igniter
hypergol cartridge?) needed for a start on the Merlin, and the engine has
fittings for only two of them, so two starts is all it's good for without
human attention. So the immediate propellant venting might not be
significant -- indeed, might have been pre-programmed -- because they
weren't going to be able to try again anyhow.
Although, hmm. They said the stage "underwent a controlled venting of
propellants". In the spirit of hermeneutical analysis (read Arocket and
improve your vocabulary!) :-), note that they don't say it was on command,
or as planned, just that it was controlled. Maybe that *wasn't* meant
to happen immediately. If the tanks vented before anything could be done
about it, that would certainly explain why they quickly gave up on trying
again.
