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> A few minutes after liftoff of SpaceX's Starlink 9-3 mission, veteran observers of SpaceX launches noticed an unusual build-up of ice around the top of the Me

> A few minutes after liftoff of SpaceX's Starlink 9-3 mission, veteran observers of SpaceX launches noticed an unusual build-up of ice around the top of the Merlin Vacuum engine, which consumes a propellant mixture of super-chilled kerosene and cryogenic liquid oxygen. [...] > Numerous chunks of ice fell away from the rocket as the upper stage engine powered into orbit, but the Merlin Vacuum, or M-Vac, engine appeared to complete its first burn as planned. A leak in the oxidizer system or a problem with insulation could lead to ice accumulation, although the exact cause, and its possible link to the engine malfunction later in flight, will be the focus of SpaceX's investigation into the failure. > A second burn with the upper stage engine was supposed to raise the perigee, or low point, of the rocket's orbit well above the atmosphere before releasing 20 Starlink satellites [...]. > "Upper stage restart to raise perigee resulted in an engine RUD for reasons currently unknown," Musk wrote... For Falcon 9 manned launches, there are a whole series of abort modes and we-didn't-get-to-orbit splashdown locations: https://www.nasaspaceflight.com/2020/05/examining-crew-dragons-launch-abort-modes-and-splashdown-locations/ https://www.nasaspaceflight.com/2020/05/examining-crew-drago... It'd be interesting to know where in this mission's flight profile, if it had been manned, the launch director would have ordered an abort. That LOX leaks often lead to explosions is Rocket Science 101.

mhandley 2y ago
If this were a manned launch, I would guess that unless the telemetry showed something very off, they would most likely have completed the full second stage burn. That would have left Dragon in a 190 x 205 km orbit, which is stable. If I understand correctly, SpaceX doesn't do orbit raising for Dragon by restarting the second stage engine (which is where the RUD happened on this Starlink launch), but rather uses Dragon's own thrusters to raise orbit. So most likely this would have been a successful flight. On Starlink flights they don't have the margin to reach a full circular orbit on a single burn. It's more efficient to achieve an eliptical orbit initially, then coast and perform a second burn at apogee. It's that second burn that proved problematic this time. Edit: having watched the videos, it would have been clear to SpaceX that they had an oxygen leak right from the start of the second stage burn. So I guess it depends on whether the pressures and flow rates within the engine looked OK. If the leak was external to the engine, then the main risk would be running of out LoX - engines really really don't like ingesting a gas bubble instead of liquid. If it looked like they were getting low on LoX, I'm sure they would have initiated one of the abort modes. Otherwise it's probably safer to continue to orbit. They do have cameras inside the tanks, in addition to all the telemetry - they have occasionally shown then on the livestream.

mhandley 2y ago

If this were a manned launch, I would guess that unless the telemetry showed something very off, they would most likely have completed the full second stage burn. That would have left Dragon in a 190 x 205 km orbit, which is stable. If I understand correctly, SpaceX doesn't do orbit raising for Dragon by restarting the second stage engine (which is where the RUD happened on this Starlink launch), but rather uses Dragon's own thrusters to raise orbit. So most likely this would have been a successful flight. On Starlink flights they don't have the margin to reach a full circular orbit on a single burn. It's more efficient to achieve an eliptical orbit initially, then coast and perform a second burn at apogee. It's that second burn that proved problematic this time. Edit: having watched the videos, it would have been clear to SpaceX that they had an oxygen leak right from the start of the second stage burn. So I guess it depends on whether the pressures and flow rates within the engine looked OK. If the leak was external to the engine, then the main risk would be running of out LoX - engines really really don't like ingesting a gas bubble instead of liquid. If it looked like they were getting low on LoX, I'm sure they would have initiated one of the abort modes. Otherwise it's probably safer to continue to orbit. They do have cameras inside the tanks, in addition to all the telemetry - they have occasionally shown then on the livestream.