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Comment by palebluedot | Hacker News Reader

Elon just tweeted: "Issue with Dragon thruster pods. System inhibiting three of four from initializing. About to command inhibit override."

Edit: https://twitter.com/elonmusk/status/307515784610058241

Edit 2: Follow-up tweet from him: "Holding on solar array deployment until at least two thruster pods are active"

Edit 3: Looking better! Latest tweet: "Thruster pod 3 tank pressure trending positive. Preparing to deploy solar arrays."

Edit 4: YES! "Solar array deployment successful"

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Update 5:20pm EST: "Orbit raising burn successful. Dragon back on track."

Update 4:10pm EST: "Thruster pods one through four are now operating nominally. Preparing to raise orbit. All systems green."

Updates from NASA News Conference 3pm EST:

* Pods 1 and 4 are pressure nominal and thrusters active.

* Pods 2 and 3 are pressure nominal and thrusters being tested; readings are optimistic; will be turned on shortly.

* NASA requires 3 of 4 pods working to enter safe zone.

* Initial indication of root cause is blockage in oxidizer pressurization system. They fixed the problem by cycling the valves.

* No leakage or debris; all systems intact.

* No rendezvous is likely in next few days.

I'm not sure if my understanding is correct, but these thruster pods are used to de-orbit the spacecraft too, right? I wonder if only one module has enough juice to de-orbit the spacecraft and retrieve it intact, if they end up needing to do that.

Yes. He said they would stay up there at least a month trying to get it to work. If they return to earth they lose one of the cargo trunks that is designed to burn up in re-entry.

The thrusters are off-center, so with only one it's hard to get any delta-v without inducing large rotation rates.

And, one last update (my edit window has passed, sorry):

"Pods 1 and 4 now online and thrusters engaged. Dragon transitioned from free drift to active control. Yes!!" https://twitter.com/elonmusk

A number of sources are now reporting that all 4 thruster pods are now online.

Looks like this may have been nothing more than a hiccup.

They do need to wait for the Dragon (and ISS) to travel a bit in their respective orbit until another opportunity comes up for rendevouz. Theres some concern that the Dragon might get too low and reenter, so they will probably have to expend fuel to stop that from happening.

Sounds like they have now successfully raised the orbit. Rendezvous is still delayed I imagine.

My understanding is that NASA gets final say, and that needs to happen about 24 hours ahead of time. I believe tomorrow afternoon NASA will make that decision, and then Dragon will go into an orbit that will intersect with ISS's.

I'm very happy. Not as happy as if there were no hiccough (SpaceX has some big enemies and they will be harping on this with the FUD), but things are playing out nicely.

Yeah. On the bright side, it is nice to see that they are able to react to unanticipated problems rapidly and effectively.

Wikipedia describes the thrusters:

Eighteen Draco thrusters are used on the Dragon spacecraft for attitude control and maneuvering. Dual-redundant in all axes: any two can fail and still have complete vehicle control in pitch, yaw, roll and translation.

Four Draco thrusters are used on the Falcon 9 second-stage as a reaction control system.

I've looked at some pictures, and I think a thruster "pod" is a collection of 4 thrusters, all pointing in different directions. It looks like there are 4 such pods arranged around the edge of the Dragon capsule. That would account for 16 or the 18 thrusters.

Two of the pods have 5 thrusters. Those pods have two thrusters point "up". That give a total of six pointing "up". These are the thrusters used for the deorbit burn and having two extra is for redundancy

Yeah, I thought the Dragon looked a bit driftier than usual, after separation. Glad to know it's alive and talking, if not necessarily in good health. Let's hope they can nurse it back.

It sounds like they're going to have to manually put it in orbit. Probably something happened to the software that auto initiates the thrusters to put it in the right trajectory. I'm just guessing as I'm no Rocket Scientist.

It's in orbit already. The question is whether they'll be able to get Dragon to the station. Most likely it's either a software bug or a faulty sensor -- the vast majority of aerospace problems are generally attributable to one or the other.

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