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

[Elmar Moelzer]

It could be a computer error. Maybe one valve was malfunctioning and the flight computer ended up proceeding as if 3 (or even all 4) had failed. Something like that could be the result of a classic copy- paste error
It is just a vague guess though. There is not enough information to form a real opinion.

[mlindner]

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?

I can't rationalize the "valve" portion of the information so I'm going to throw that out as information for now and going to assume its something like a widespread event and one thruster quad managed to avoid the event. Something like heavy ice buildup everywhere and only one quad managed to avoid it by luck.

[R7]

Something like heavy ice buildup everywhere and only one quad managed to avoid it by luck.

Why ice, the props aren't cryogenic.

[Elmar Moelzer]

Something like heavy ice buildup everywhere and only one quad managed to avoid it by luck.

Why ice, the props aren't cryogenic.

well they did say at one point that it was pretty cold in Florida that day...
Not sure whether that would make a difference though. I still prefer to think software error...

[mlindner]

Something like heavy ice buildup everywhere and only one quad managed to avoid it by luck.

Why ice, the props aren't cryogenic.

well they did say at one point that it was pretty cold in Florida that day...
Not sure whether that would make a difference though. I still prefer to think software error...

Being a software engineer I somehow doubt that's the issue. Software bugs don't tend to be so odd as to take out 3 of something but not a 4th. It is either only 1, by radiation hit, all of them by software failure, or none of them.

[Elmar Moelzer]

Something like heavy ice buildup everywhere and only one quad managed to avoid it by luck.

Why ice, the props aren't cryogenic.

well they did say at one point that it was pretty cold in Florida that day...
Not sure whether that would make a difference though. I still prefer to think software error...

Being a software engineer I somehow doubt that's the issue. Software bugs don't tend to be so odd as to take out 3 of something but not a 4th. It is either only 1, by radiation hit, all of them by software failure, or none of them.

I am a software developer and copy paste errors are common. It would explain why something works for one thing and not the others (because e.g. they cant work if the code does not match the hardware). It is all pure speculation at this point anyway.

[mmeijeri]

Getting out of the way of the press conference...

Thanks I was not aware of the precession issue. I always catch myself thinking in terms of orbital rendezvous in kerbal space program which has non-precessing orbits. Couldn't a burn at one of the crossing points of the precessed orbits correct for this, depending on fuel amounts?

Yes, but as danderman noted the fuel amount required for the plane change will increase with time. 5-6 days is his SWAG but there is definitely a point beyond which rendezvous is no longer possible.

If it waits long enough, does it become possible again? Isn't Dragon supposed to have an autonomous endurance of about 6 months? It probably wouldn't make sense to keep trying for that long. What is the longest period they could realistically wait and still be useful? Long enough for another alignment?

[LouScheffer]

I'm having trouble visualizing any (rational) configuration where problems with one valve  could knock out 3 out of four pods. 

I can't rationalize the "valve" portion of the information so I'm going to throw that out [...]

Sure, but as armchair incident investigators we have only two facts - only 1 quad was working, and they blamed it on 'a value'.  Throwing away half the facts seems rash.  And the combination of clues seems very powerful - there cannot be many scenarios that produce this, if this group cannot come up with even one.  (I'm not counting the generic 'software error' since that can produce any effect whatsoever, and hence has no predictive value.)

[Jim]

3 of 4 valves "failed" to work properly.  Looks like something systemic or procedural.

[Galactic Penguin SST]

On the teleconference it was mentioned that it may be a stuck valve.

Be careful about assessing root cause too early, one possibility is some blockage in the ox pressurization, which we freed. Or maybe a stuck valve which we unstuck. Cycling the valves to pressure hammer them did it. As always till we have more time hard to say, just a guess.

[Elmar Moelzer]

They seem to have attributed it to a hardware issue with valves that got stuck and/ or some sort of blockage that they were able to "shake loose". Strange!

[krytek]

How the hell do you pressure hammer a blockage in the oxidizer/fuel lines?

[Galactic Penguin SST]

OK someone please remind me if those Draco thrusters are pressure fed or pump fed..... 

[ugordan]

Pressure fed.

[JWag]

OK someone please remind me if those Draco thrusters are pressure fed or pump fed..... 

Pressure-fed with Helium.  Pumps take too much time to spool up; thrusters need to be immediate.

[krytek]

OMG
Did Elon just say they're gonna have no solar panels for Crew Dragon?!

[reubenb]

Yeah, he said no solar arrays for ISS missions, just a big battery.  There will be solar arrays for longer duration missions.

[Kabloona]

How the hell do you pressure hammer a blockage in the oxidizer/fuel lines?

You cycle the He isolation valve open/closed/open/closed.

[Kabloona]

Elon saying possibly stuck check valve(s) on the He pressurant lines to the ox tanks. Says only one of four ox tanks initally had full He pressure.

[manboy]

yeah, interesting.  no solar on crewed dragon.  straight from the horse's mouth.

Is this to save mass that they would go this route, didn't catch all his answer on this.

Didn't say, but if the battery is internal, it could be part of keeping Dragon as reusable as possible.

Good point.