LOX/Methane has the added feature that the boiloff from any pool of
mixed propellants, will often produce a detonable vapor cloud over the
pool of detonable liquid explosive. That makes it much easier to couple
a stray ignition source anywhere in the vicinity into a full-yield
detonation. LOX/propane will also do that, but most of the other
combinations won't. And yes, the initiation energy of mixed LOX/methane
is exceedingly low.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0855
On 7/27/2019 12:23 PM, Ben Brockert wrote:
This is true of any miscible propellant, we’ve discussed it here many times. It does make horizontal engine testing harder, you have to be sure the chamber is clear after doing any injector chilling flows before ignition. I had a small detonation for failing to do that.
Also applies to LOX/propane, LOX/some other hydrocarbons, peroxide/alcohol, nitrous/many things.
Even in non-miscible propellants like LOX/isopropyl it’s good to watch out for “blue jelly” in the event of combined propellant spills.
On one test SpaceX unintentionally failed a dome leading to mixing of a full rocket of LOX and RP. By some great luck it eventually boiled off without exploding. The initiation energy of mixed LOX/methane is probably lower, would definitely be best to not repeat that experiment.
Ben
On Saturday, July 27, 2019, John Schilling <john.schilling@xxxxxxxxxxxxxx <mailto:john.schilling@xxxxxxxxxxxxxx>> wrote:
On 7/27/2019 8:03 AM, James Fackert wrote:
Somehow I think they may have planned for such a thing ..all
that burning methane and stuff...
jim fackert
Brush fires are one of the more benign failure modes for burning
methane. Without going into still-proprietary details,
LOX+methane has failure modes that more traditional propellants,
and while I know that ULA and Blue Origin are both working to
quantify and mitigate the hazards, I haven't heard of SpaceX
working along those lines. Hopefully they're just being secretive
rather than overconfident.
In the meantime, anyone here planning to use LOX/methane would be
well advised to,
1. Make extra damn sure they don't mix during any plausible
failure, e.g. be suspicious of common-bulkhead tanks or running
one set of propellant lines through the other tank. Flame trenches
shouldn't have sumps that can collect spilled propellants. Etc.
2. If they do mix, it's probably best if they ignite *immediately*.
3. If they mix without immediately igniting, assume possible 200%
TNT equivalence until you're sure everything has boiled off.
That's probably an overestimate, but it may not be a huge one.
I'll send a heads-up to the list as soon as quantitative test
results and risk-mitigation recommendations are released, but that
will probably be a few months.
John Schilling
john.schilling@xxxxxxxxxxxxxx <mailto:john.schilling@xxxxxxxxxxxxxx>
(661) 718-0955
