Actually, the risky part with Starliner is way before reentry. The problem is they have to undock, and fly around the ISS in a sort of loop combined with an end-over-end tumble to get the retro rockets facing in the direction of flight before they do a de-orbit burn.
Needless to say, that uses the RCS thrusters a lot, and if they fail at the wrong point the capsule ends up facing the wrong way or stuck in a tumble and can't de-orbit... or in the worst case, it does the de-orbit burn facing the wrong way and crashes into the ISS!
They've simplified the undocking manoeuvres a lot however, only doing one step at a time, so if an RCS unit goes kaput it's not a total loss and might be recoverable. (apparently the fix is to turn them off and back on again!) But like you say, NASA is not taking chances any more!
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Actually, the risky part with Starliner is way before reentry. The problem is they have to undock, and fly around the ISS in a sort of loop combined with an end-over-end tumble to get the retro rockets facing in the direction of flight before they do a de-orbit burn.
Needless to say, that uses the RCS thrusters a lot, and if they fail at the wrong point the capsule ends up facing the wrong way or stuck in a tumble and can't de-orbit... or in the worst case, it does the de-orbit burn facing the wrong way and crashes into the ISS!
They've simplified the undocking manoeuvres a lot however, only doing one step at a time, so if an RCS unit goes kaput it's not a total loss and might be recoverable. (apparently the fix is to turn them off and back on again!) But like you say, NASA is not taking chances any more!