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What is an 'actuator drift' problem? My google fu only returned stories about this aborted launch and this article (http://hydraulicspneumatics.com/other-techno

by winslow 12y ago

What is an 'actuator drift' problem? My google fu only returned stories about this aborted launch and this article (http://hydraulicspneumatics.com/other-technologies/truth-about-problem-valves http://hydraulicspneumatics.com/other-technologies/truth-abo...). Is my understanding correct that a valve/piston was moving when it wasn't suppose to? What type of dangers could this impose of the rocket/vehicle?

BrandonMarc 12y ago
/r/spacex tipped me off to this 4-year-old video, which shows off what a Thrust Vector Control test stand does, and how testing of actuators, etc is related to sensing engine / control-surface anomalies. https://www.youtube.com/watch?v=Pigsq5rt-mY https://www.youtube.com/watch?v=Pigsq5rt-mY Heh, and it turns out it's a SpaceX video.
- winslow 12y ago
  Awesome! Thanks for the video. The frequency in which it changes position is really interesting. Didn't realize the movement involved.
jccooper 12y ago
You are probably correct: the piston on the actuator is moving differently than it's supposed to and/or rough at maintaining position. Probably a hydraulic valve is set wrong or broken to cause that. Could also be a leak, I suppose. There could also be servomotor/encoder problems, but that's less likely. That actuator is attached to the upper-stage engine, and moves it in one of its axes to steer the rocket via changing (slightly) the direction of the thrust. If it is unable to steer as commanded, or (worse) goes in a different direction than commanded, the rocket stage will have a bad day. It could hit the wrong trajectory, or it could spin out of control. A first stage could be destroyed by turning too hard, but probably not a second. They appear to use them in opposing pairs, so probably the other one would be able to fight any problems with its partner. But you want everything to work as well as it can on rockets. Probably they'll swap the part and try for the next window.

by winslow 12y ago

BrandonMarc 12y ago

/r/spacex tipped me off to this 4-year-old video, which shows off what a Thrust Vector Control test stand does, and how testing of actuators, etc is related to sensing engine / control-surface anomalies. https://www.youtube.com/watch?v=Pigsq5rt-mY https://www.youtube.com/watch?v=Pigsq5rt-mY Heh, and it turns out it's a SpaceX video.

winslow 12y ago
Awesome! Thanks for the video. The frequency in which it changes position is really interesting. Didn't realize the movement involved.

jccooper 12y ago

You are probably correct: the piston on the actuator is moving differently than it's supposed to and/or rough at maintaining position. Probably a hydraulic valve is set wrong or broken to cause that. Could also be a leak, I suppose. There could also be servomotor/encoder problems, but that's less likely. That actuator is attached to the upper-stage engine, and moves it in one of its axes to steer the rocket via changing (slightly) the direction of the thrust. If it is unable to steer as commanded, or (worse) goes in a different direction than commanded, the rocket stage will have a bad day. It could hit the wrong trajectory, or it could spin out of control. A first stage could be destroyed by turning too hard, but probably not a second. They appear to use them in opposing pairs, so probably the other one would be able to fight any problems with its partner. But you want everything to work as well as it can on rockets. Probably they'll swap the part and try for the next window.