It's at the head end where the LOx injector and prop valve is located if
you understand how a hybrid rocket motor is configured. The ball has a
venturio built into it so it acted like a cavitating venturi when fully
opened. Since I was invited to the launch with access to the crew
their 20/20 hindsight was a trickle purge would have prevented ice build up
on the valve something that didn't happen at the test facility in the dry
air of the Mojave desert. Being somewhat embarrassing this info was not
passed on to the general public.
Ken
On Mon, Mar 15, 2021 at 6:26 PM Norman Yarvin <yarvin@xxxxxxxxxxxx> wrote:
So this is a purge of the compartment surrounding the valve?
(Flow inside the plumbing is what people here usually mean when using
the word 'purge', so there may be misunderstanding.)
On Mon, Mar 15, 2021 at 10:54:26AM -0700, roxanna Mason wrote:
You're missing the point of a "trickle" purge. It's only purpose is tokeep
the relative humidity below the dew point. A K cylinder would last all daywere
and a facility like at Vandenburg would have millions of Ft3 of facility
gas on tap.
The failure mode was frost/ice condensed on the surface of the ball and
kept it from fully rotating full open. A 1 Ft3/min purge would have
prevented this mishap but they never needed it at the desert facility at
Edwards and nobody had the foresight to think of it only a few hundred
yards from the pounding surf of the Pacific Ocean.
Ken
On Mon, Mar 15, 2021 at 4:11 AM Ben Brockert <wikkit@xxxxxxxxx> wrote:
On Mon, Mar 15, 2021 at 3:59 AM roxanna Mason
<rocketmaster.ken@xxxxxxxxx> wrote:
And FWIW some history, me along with 3 other Truax Engineering reps
theyinvited to that launch at Vandenberg AFB. They made one fatal error,
venturididn't incorporate a trickle purge at the head end of the motor where
frost/ice condensed on the LOx valve which was a ball valve with a
approxconture that froze the ball. When commanded to open the ball rotated
which10-20% allowing just enough LOx to flow for an ignition but slow burn
taildidn't have enough thrust to lift the rocket but instead burned up the
burnedend supporting the rocket which collapsed the rocket on its side and
whereup, as William pointed out. The irony was that in the Mojave desert
neverall the static testing was done had such low humidity that frost was
Aa problem. This problem should have been anticipated though but wasn't.
trickle purge should always be used with the motor open to the elements.
I've fired LOX rockets in a lot of climates and have never run
continuous injector purge. It's basically impossible for a purge to
keep a valve warm if there's LOX on the other side of it. You could
design the flow path to have a bubble on the valve, but from the
description my root cause would go more toward "actuator power was
marginal" and "system aborts were not designed well".