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I noticed a delay between video and audio - the announcer on the NASA official live broadcast said splashdown before the the capsule splashed down on video. Wa

I noticed a delay between video and audio - the announcer on the NASA official live broadcast said splashdown before the the capsule splashed down on video. Was it intentional (in case something happened)? Also, what were these puffs on thermal camera after the main chutes were deployed? https://www.youtube.com/live/m3kR2KK8TEs https://www.youtube.com/live/m3kR2KK8TEs

shoghicp 5mo ago
RCS (Reaction Control System) which you can see on Artemis I internal video as it falls down https://www.youtube.com/watch?v=-QbYrs5SZ5M https://www.youtube.com/watch?v=-QbYrs5SZ5M
llbbdd 5mo ago
I was wondering about that too, I assume maybe there was some additional adjustments needed to land in the right spot, but they didn't mention it on the stream.
- java-man 5mo ago
  Yeah, they looked intentional - there are no reaction wheels on the capsule.
hydrogen7800 5mo ago
My suspicion was they were burning excess propellant, rather than attitude adjustment while under the parachutes. Though who knows how much propellant remained. It could be quite a bit more than it appears was used.
- devilbunny 5mo ago
  Not just excess - excess and toxic. Hydrazine derivatives and nitrogen tetroxide, IIRC. They are hypergolic, too, so the easiest way to vent them is just to run the engines until empty. However, to prevent moving the craft too much, you do short bursts.
  - TomatoCo 5mo ago
    There should be an opposite thruster for each axis. I wonder if the short bursts were due to heating limits.
    - devilbunny 5mo ago
      There are opposed thrusters, but I assume that in atmosphere and under parachute canopy it’s harder to make sure they are perfectly opposed. Heating likely plays a role as well. I am not a rocket engineer, but I have read How Apollo Flew to the Moon and Ignition!: an informal history of liquid rocket propellants, both of which cover these issues. Highly recommended.
    - _moof 5mo ago
      The short bursts are just the period of the control cycles. Control cycle starts, loop sees error, commands thrust; next control cycle starts, loop sees error is nulled (or in deadband), commands no thrust.
  - m4rtink 5mo ago
    On the press conference they mentioned the RCS was used to orient the craft with the most sturdy part facing down for the ocean impact. Otherwise I would also just bet on RCS venting like in Apollo.
- hydrogen7800 5mo ago
  In the post splashdown conference, they mentioned that these were indeed attitude control bursts to orient for favorable orientation for water impact.
- _moof 5mo ago
  It was for attitude adjustment.

shoghicp 5mo ago

RCS (Reaction Control System) which you can see on Artemis I internal video as it falls down https://www.youtube.com/watch?v=-QbYrs5SZ5M https://www.youtube.com/watch?v=-QbYrs5SZ5M

llbbdd 5mo ago

I was wondering about that too, I assume maybe there was some additional adjustments needed to land in the right spot, but they didn't mention it on the stream.

java-man 5mo ago
Yeah, they looked intentional - there are no reaction wheels on the capsule.

hydrogen7800 5mo ago

My suspicion was they were burning excess propellant, rather than attitude adjustment while under the parachutes. Though who knows how much propellant remained. It could be quite a bit more than it appears was used.

devilbunny 5mo ago
Not just excess - excess and toxic. Hydrazine derivatives and nitrogen tetroxide, IIRC. They are hypergolic, too, so the easiest way to vent them is just to run the engines until empty. However, to prevent moving the craft too much, you do short bursts.
- TomatoCo 5mo ago
  There should be an opposite thruster for each axis. I wonder if the short bursts were due to heating limits.
  - devilbunny 5mo ago
    There are opposed thrusters, but I assume that in atmosphere and under parachute canopy it’s harder to make sure they are perfectly opposed. Heating likely plays a role as well. I am not a rocket engineer, but I have read How Apollo Flew to the Moon and Ignition!: an informal history of liquid rocket propellants, both of which cover these issues. Highly recommended.
  - _moof 5mo ago
    The short bursts are just the period of the control cycles. Control cycle starts, loop sees error, commands thrust; next control cycle starts, loop sees error is nulled (or in deadband), commands no thrust.
- m4rtink 5mo ago
  On the press conference they mentioned the RCS was used to orient the craft with the most sturdy part facing down for the ocean impact. Otherwise I would also just bet on RCS venting like in Apollo.
hydrogen7800 5mo ago
In the post splashdown conference, they mentioned that these were indeed attitude control bursts to orient for favorable orientation for water impact.
_moof 5mo ago
It was for attitude adjustment.