JF Mezei wrote on Mon, 29 Apr 2019
17:00:46 -0400:

On 2019-04-29 09:38, Fred J. McCall wrote:

I consider it unlikely in the extreme. I'd consider the likely causes
here to be a pressure vessel or pressure line failure or a combustion
chamber failure. I'm sure there are lots of other possible failure
modes.


Would the hypergolic tanks need to be highly pressurized? What is
needed is for the liquid components be pushed through pipes to
combustion chamber right?


Right, which means you need pressure that exceeds the combustion
chamber pressure. That implies either highly pressurized tanks,
really powerful pumps, or both. It's usually done with highly
pressurized tanks because that's the simpler approach (fewer moving
parts) and the point behind hypergolic engines is simplicity and
reliability.


How would the hypergolic tanks be configured? are they like a piston,
normally with no pressure, but when needed, helium is pushed on one side
of piston to push the fuel out the other end ? or just pumping helium
into the bank hoping the fuel is at the "exit" end ? Are the tanks
normally under pressure or is pressure applied only when engines are fired ?


My expectation would be that the tanks would always be pressurized and
that engine firing is controlled by throttle valves. Again, simplest
and most reliable approach.


We may have seen an explosion, but it has no context in terms of
timeline. Were they filling tanks? did explosion happen while noting was
happening? or happen when they fired the engines ?


Exactly the point. Since they were going into an engine test I'd
expect the tanks would already be filled long before. Again, these
are not cryogenic fluids and there's not a "we want them as cold as
possible". Remember, in normal use these tanks may sit for a LONG
time before the engines get used, since they're not normally using
during an ascent. I'd expect the explosion happened either very
shortly before or right at 'engine ignition' time.


This may have nothing to do with actual engines. It it may.


I find it doubtful that there is a systemic design flaw with all the
fire time that these engines have had. I'm leaning toward a 'one off'
manufacturing flaw or mechanical failure involving a pressure vessel,
tank, feed line, or combustion chamber. But I don't know any more
than anyone else, not having the exact timeline and telemetry.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden