Astrobotic PM-1 mission, CLPS mission with NASA and commercial payloads Options

[Phil Stooke]

I am starting a new thread for this mission which should fly this year.

Phil

[Thorsten Denk]

Update #6:
"An ongoing propellant leak [...]"
"[...] in a stable sun pointing state for approximately 40 more hours, [...]"
https://twitter.com/astrobotic/status/1744543629392134194

Anything known about what caused this propellant leak?

Thorsten

[mcaplinger]

Anything known about what caused this propellant leak?

I haven't heard anything, and there is not much public detail about Peregrine's propulsion system. But it started right after the system was pressurized and was large enough to disturb blankets. I can think of three root causes: 1) damage during launch vibration (hopefully unlikely since the spacecraft was vibe-tested); 2) propellant migration causing a small explosion that blew a hole in the plumbing; 3) pressure regulator failure leading to overpressurization. Assuming https://www.nasa.gov/stmd-game-changing-dev...in-space-talos/ describes what they ended up flying, the main engines were MON-25/MMH biprops but how the attitude-control thrusters (presumably monoprops) were tied in, I have not seen.

[mcaplinger]

...3) pressure regulator failure leading to overpressurization.

Astrobotic is now saying

Astrobotic’s current hypothesis about the Peregrine spacecraft’s propulsion anomaly is that a valve between the helium pressurant and the oxidizer failed to reseal after actuation during initialization. This led to a rush of high pressure helium that spiked the pressure in the oxidizer tank beyond its operating limit and subsequently ruptured the tank.

This seems odd to me, since usually such a valve would open just once and then a downstream regulator would maintain system pressure at the desired safe level. But it sounds like they tried to avoid needing a regulator by just burping the valve open briefly (in hindsight maybe not such a good idea.)

[rlorenz]

This seems odd to me, since usually such a valve would open just once and then a downstream regulator would maintain system pressure at the desired safe level. But it sounds like they tried to avoid needing a regulator by just burping the valve open briefly (in hindsight maybe not such a good idea.)

Cassini operated this way. I mean, it wasnt designed to operate this way (see my Haynes Cassini-Huygens Owners Workshop Manual) - it had a regulator, but somehow the regulator stuck open with a high leak rate - not enough to pop the propellant tank right away, thankfully, so the operators were able to close the upstream latch valve (which turned out to have a rather lower leak rate than specc'd, fortunately) and burped it later to maintain the ullage pressure as the fuel depleted. Sounds like Peregrine jumped to that approach - higher risk, but simpler/lighter

Biprops are hard to get right - a lot of failures/anomalies attributable to this piece of the system - Mars Observer, Akatsuki, Cassini, JUNO.....

[Edomann]

Cassini operated this way. I mean, it wasnt designed to operate this way (see my Haynes Cassini-Huygens Owners Workshop Manual) - it had a regulator, but somehow the regulator stuck open with a high leak rate - not enough to pop the propellant tank right away, thankfully, so the operators were able to close the upstream latch valve (which turned out to have a rather lower leak rate than specc'd, fortunately) and burped it later to maintain the ullage pressure as the fuel depleted. Sounds like Peregrine jumped to that approach - higher risk, but simpler/lighter

Biprops are hard to get right - a lot of failures/anomalies attributable to this piece of the system - Mars Observer, Akatsuki, Cassini, JUNO.....

Isn’t it usual to use a pyrotechnic valve to isolate the He tank? Solenoid valves present the risk of valve bounce during periods of very high vibration during the launch; the valve stem lifts off the seat. The pyrovalve provides a hermetic seal until the charge is ignited, so it ensures zero leakage during the launch phase and is only fired when that is complete.

I know that the thrusters on the mission have no previous flight heritage; I’m wondering whether other fluid-flow components in the propulsion system also lack heritage.

Ed

[mcaplinger]

Isn’t it usual to use a pyrotechnic valve to isolate the He tank? Solenoid valves present the risk of valve bounce during periods of very high vibration during the launch; the valve stem lifts off the seat. The pyrovalve provides a hermetic seal until the charge is ignited, so it ensures zero leakage during the launch phase and is only fired when that is complete.

Of course. The Peregrine leak only started after the Triton Space pyrovalves were fired. They apparently worked fine and the issue was downstream.

I know that the thrusters on the mission have no previous flight heritage; I’m wondering whether other fluid-flow components in the propulsion system also lack heritage.

Possibly not, but heritage only goes so far. The components on Cassini and Juno had tons of heritage, but that didn't keep them from misbehaving.