SpaceX CRS-5 launch aborted, next attempt Friday | Hacker News Reader

SpaceX CRS-5 launch aborted, next attempt Friday

blogs.nasa.gov

66 pointskid0m4n14 comments

https://twitter.com/Cmdr_Hadfield/status/552432830912151552

> Launch scrubs reassure me. It means that the powerful desire to GO has been tempered by the necessity to be truly ready. Cool heads @SpaceX

The launch abort was automated, so heads didn't need to be cool. I'm not sure if that makes it more reassuring or less.

The abort would have been automatically triggered had they not manually initiated it.

My understanding is that while the abort was automated, it was triggered because the engineers manually held the countdown and the launch window was only one second. Humans set the automatic limits, anyways.

It wasn't automated. It was an operator calling hold.

For fun, here's the part probably in question:

http://jasc-controls.com/jasc-industry-listing/space/space-a...

A servo-controlled hydraulic linear actuator with redundant coils in the servomotor. Probably runs using the RP-1 fuel as hydraulic fluid.

I listened to the last minutes of the stream, and I was impressed at how speedy their voices were.

I don't recall hearing such haste in Nasa's launches; it was a bit weird and exciting at the same time.

It reminds me a lot of listening to air traffic control somewhere busy.

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-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?

/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

Heh, and it turns out it's a SpaceX video.

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

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.

This makes me wonder just how many sensors they have devoted entirely to detecting problems before, during, and after lift-off.

My guess would be (2 x the number of critical mechanisms) 1, primary sensor and 1 backup to make sure that one doesn't provide a false positive

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