4 ms·

AFTS activation indicates deviation from planned trajectory. It's unusual, being so late in the burn. Could be a guidance issue, but SpaceX should be pretty go

AFTS activation indicates deviation from planned trajectory. It's unusual, being so late in the burn. Could be a guidance issue, but SpaceX should be pretty good at that by now. Could be engine underperformance, but we got nominal callouts and it would have to be pretty bad for AFTS to notice with minutes left, so that seems unlikely. I'd guess engine control (due to damage during staging) is the main suspect. We say the thrusters fighting pretty hard there at the end, which supports that idea.

goku12 3y ago
I wonder if something happened at around T+7:39. There is a rather sudden and large plume when the starship should've been in steady state.
lutorm 3y ago
I dunno, it looks like a nominal shutdown to me. The speed readout shows rapidly decreasing acceleration just as the engine displays go out instead of the telemetry suddenly going stale as you'd expect if it just blew up during the burn. Then, after the acceleration has gone to zero, the telemetry goes stale, so my guess would be on something going wrong during shutdown (ullage collapse when the propellant sloshes forward as the engines shut down maybe, this was a problem during the first landing test.) AFTS seems unlikely this late in the burn, I think they said it was in terminal guidance and it's very hard to laterally change the impact point in any meaningful way with that much velocity. But I agree, it definitely looked like something's venting near the end, too.
- jltsiren 3y ago
  Starship engines were cut off at 8:03, while the nominal mission profile in Wikimedia mentions SECO at 8:33. The speed at cutoff was ~24000 km/h at an altitude of ~150 km. Without the AFTS, the Starship would have crashed somewhere in the Atlantic.
  - lutorm 3y ago
    Yes, good point, the velocity was too low. Yet it looked like all the engines just shut down nominally.
- rpmisms 3y ago
  Manley's fluid hammer theory from rapid shutdown is compelling. Also would explain the large vapor clouds; plumbing exploded.

goku12 3y ago

I wonder if something happened at around T+7:39. There is a rather sudden and large plume when the starship should've been in steady state.

lutorm 3y ago

I dunno, it looks like a nominal shutdown to me. The speed readout shows rapidly decreasing acceleration just as the engine displays go out instead of the telemetry suddenly going stale as you'd expect if it just blew up during the burn. Then, after the acceleration has gone to zero, the telemetry goes stale, so my guess would be on something going wrong during shutdown (ullage collapse when the propellant sloshes forward as the engines shut down maybe, this was a problem during the first landing test.) AFTS seems unlikely this late in the burn, I think they said it was in terminal guidance and it's very hard to laterally change the impact point in any meaningful way with that much velocity. But I agree, it definitely looked like something's venting near the end, too.

jltsiren 3y ago
Starship engines were cut off at 8:03, while the nominal mission profile in Wikimedia mentions SECO at 8:33. The speed at cutoff was ~24000 km/h at an altitude of ~150 km. Without the AFTS, the Starship would have crashed somewhere in the Atlantic.
- lutorm 3y ago
  Yes, good point, the velocity was too low. Yet it looked like all the engines just shut down nominally.
rpmisms 3y ago
Manley's fluid hammer theory from rapid shutdown is compelling. Also would explain the large vapor clouds; plumbing exploded.