What Henry said. Cubed. The benefits, to the incident investigation if
nothing else, of eliminating failure modes cannot be overstated.
-R
On Mon, Apr 25, 2016 at 12:58 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 20 Apr 2016, snyder@xxxxxxxxxx wrote:
...I noticed the common pressurant system for both Fuel and Oxidizer andinitially.
strongly suggest separate systems (Tanks) for several reasons. ...
Now, an actual flying system may have all sorts of goofyness in it, but
for a baseline test stand, remove as many variables as possible
Even flight systems these days are increasingly cautious about this sort
of thing.
The common pressurization system is a strong suspect as the cause of the
loss of the Mars Observer spacecraft, to the point that modern spacecraft
often have either entirely separate fuel and oxidizer pressurization, or
only the helium tank in common. (I've seen one design, I think it was
MESSENGER, that had one helium tank with two separate outlets, so there
was *no* plumbing in common between the two sides.)
Spacecraft are a more severe case than rockets in some ways, like longer
duration... but some of those problems come back when you move the rocket
hardware from a flight rocket to a test stand. A rocket may need to be
pressurized for only a few minutes, but a test stand might sit there under
pressure for half a day while you, say, troubleshoot misbehaving
instrumentation.
Test stands are (you hope!) where you make your mistakes and find your
problems. Best to make them as robust and bulletproof as possible. Not
only does it reduce the number of loud surprises, but also, knowing that
nasty problem X just can't occur, no matter how you mess up, means you
don't have to analyze for it or take precautions against it or write an
emergency procedure for it. The more problems you preclude by design, the
more quickly and easily you'll get your hardware onto the test stand.
Henry
