Somehow I missed what out of this world happened to result in some people stranded in space, and I thought it’d be fun/interesting to see how others describe what led to it.
Somehow I missed what out of this world happened to result in some people stranded in space, and I thought it’d be fun/interesting to see how others describe what led to it.
It’s actually a lot worse than just thrusters not working any more. At least according to the unofficial “word on the street” about what’s going on, the details haven’t been officially released yet.
It appears that the cause of the failures was because the thrusters are housed inside compartments that are containing their waste heat. The thrusters were tested individually, but apparently were never tested once installed inside the capsule. The heat is causing teflon valves to fail, which clogs the thruster plumbing and disables them. But the scary thing is that the heat necessary to do that to teflon would also potentially be enough to boil the hypergolic fuel itself inside the fuel lines.
When you heat hypergolic fuel up enough it will spontaneously ignite. It’s got its own oxidizer in it, essentially. Which means those thrusters could well be bombs that could go off if they’re fired too long.
The way they’re talking about moving the unmanned capsule away from ISS, slowly and gently, it sounds like they’re concerned Starliner could literally explode next to the station. That would be, to put it mildly, very very bad.
If any of this is true then this is going to be a colossal scandal. This is Starliner’s third test flight, it’s absolutely incredible that Boeing wouldn’t have figured this out by now and that NASA let them get away with such a shoddy program.
Kinda. The RCS is fueled by two fluids that spontaneously combust when mixed: N2H4 and N2O4, aka hydrazine and nitrogen tetroxide (or dinitrogen tetraoxide).
If the N2H4 gets hot enough, it will exothermically decompose into a large volume of hot gas. Its sometimes used as a monopropellant - squirt some of it onto a catalyst and direct the gas out a rocket nozzle, and you’ve got a simple, reliable thruster. Mixing it with N2O4 produces hotter gas, resulting in a thruster that gets about 35% higher fuel efficiency.
Problems with the helium system could make hydrazine decomposition in the fuel lines more likely to happen. One of the ways the hydrazine is kept cool while its in the fuel lines is via high flow rate, but that requires the fuel tank to be pressurized by helium - clearing the fuel lines after thruster shutdown may also require helium. Low pressure could lead to lower flow rate and possibly cause cavitation (which can cause tiny spots of very high heat), which could in turn cause the hydrazine to decompose in the fuel lines/tank. At that point, mixing with N2O4 would be overkill - Starliner would already be destroyed before the oxygen started burning.
Thanks for the clarification. Wasn’t sure how down into the weeds of why Starliner would go boom I should go, but this is clear and I should have been more specific about the “hypergolic” term.
Is it really that incredible, though? It’s Boeing after all.