SpaceX Falcon 9/Dragon CRS-2 SpX-2 MISSION GENERAL DISCUSSION

[hop]

Once you start reentering ballistically and develop significant drag, I don't think you need ANY attitude control for a passively stable reentry vehicle.

Not true, depends on the vehicle design whether it is passively stable. Whether you end up heat shield forward in a completely passive entry also depends on the vehicle. Soyuz does this pretty well (see Soyuz 5...), not sure about Dragon.

[Robotbeat]

Once you start reentering ballistically and develop significant drag, I don't think you need ANY attitude control for a passively stable reentry vehicle.

Not true, depends on the vehicle design whether it is passively stable. ...

Notice the part in bold...

FWIW, I also am not sure whether Dragon is passively stable, but it has a strong potential for being passively stable given it is a capsule.

[manboy]

My prediction is that they won't make it to the ISS, I hope I'm wrong.

[R7]

SC can be passively stable and still end up entering nose first, if that attitude is stable too. Mercury was like that, hinged metal flap was added to guarantee proper orientation.

[mlindner]

My prediction is that they won't make it to the ISS, I hope I'm wrong.

That would only happen if NASA feels they don't want to risk it. SpaceX wouldn't give up till they achieved it.

[Robotbeat]

SC can be passively stable and still end up entering nose first, if that attitude is stable too. Mercury was like that, hinged metal flap was added to guarantee proper orientation.

Of course, so they'll need a certain amount of attitude control at first when the start reentry, but it should be good after that.

[ugordan]

SpaceX wouldn't give up till they achieved it.

That's rather naive. You think controlling a spacecraft with 1 thruster quad is easy/doable? There is a limit to doing "miracles", even with SpaceX.

[mlindner]

SpaceX wouldn't give up till they achieved it.

That's rather naive. You think controlling a spacecraft with 1 thruster quad is easy/doable? There is a limit to doing "miracles", even with SpaceX.

I'm maintaining that they got a second quad working so they have attitude control.

[Robotbeat]

SpaceX wouldn't give up till they achieved it.

That's rather naive. You think controlling a spacecraft with 1 thruster quad is easy/doable? There is a limit to doing "miracles", even with SpaceX.

I'm maintaining that they got a second quad working so they have attitude control.

Need 3 pods before approaching station, according to NASA.

[R7]

Any info on how the pods are numbered? Which ones have 5 thrusters etc?

[Jim]

SpaceX wouldn't give up till they achieved it.

That's rather naive. You think controlling a spacecraft with 1 thruster quad is easy/doable? There is a limit to doing "miracles", even with SpaceX.

I'm maintaining that they got a second quad working so they have attitude control.

Unsubstantiated.

[yg1968]

I guess that it is safe to say that pushing the override button didn't work. At this point, is it safe to say that it is not a software problem?

[Borklund]

It pains me to write this, but Jim is right. Most likely scenario according to the info you can piece together is that they have 1 quad working and that they got NASA to agree to let them deploy solar panels with only one quad. There's no info to say that two quads are working.

[Herb Schaltegger]

It pains me to write this, but Jim is right. Most likely scenario according to the info you can piece together is that they have 1 quad working and that they got NASA to agree to let them deploy solar panels with only one quad. There's no info to say that two quads are working.

I don't think SpaceX needs NASA approval to deploy their own solar arrays. 

[ugordan]

they got NASA to agree to let them deploy solar panels with only one quad.

Why would they need NASA's permission to do that? It's their vehicle and they're doing whatever they think helps recovery, NASA doesn't get much say about it until its rendezvous time - which seems less and less likely to happen here.

[Borklund]

I must have gotten that bit wrong then; IIRC someone said that solar arrays wouldn't deploy with one quad?

[mlindner]

I must have gotten that bit wrong then; IIRC someone said that solar arrays wouldn't deploy with one quad?

Solar arrays didn't deploy because the automatic ordering of events got interrupted which shoved Dragon into a passive abort drift. Thus it waited till it got a command to do further actions.

[ugordan]

I must have gotten that bit wrong then; IIRC someone said that solar arrays wouldn't deploy with one quad?

Because they decided to unfold the arrays anyway, as per the one-and-only SpaceX press release. What's it have to do with NASA, either way?

[Lar]

Because they decided to unfold the arrays anyway, as per the one-and-only SpaceX press release. What's it have to do with NASA, either way?

I would think not much. I also thought these missions were paid for by NASA on a "cargo delivered" basis, meaning that if Dragon doesn't dock and cargo can't be delivered, no payment for upmass and if Dragon doesn't return safely, no payment for downmass. [1]

So of course SpaceX would want to do everything possible to dock. And NASA will want to do everything reasonable to keep ISS safe. That sets up a tension, potentially, which will be interesting.

ALL uninformed speculation based on possibly faulty memory.

1 - This is how i would structure it if I were paying, cash on delivery.

[LouScheffer]

I'm having trouble visualizing any (rational) configuration where problems with one valve (and the press release said 'a valve') could knock out 3 out of four pods.  All four, sure.  Two out of 4?  Makes perfect sense.  But three  out of four makes no sense.  Maybe mis-plumbing?