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

[Jim]

Well, it's a theory.  But you'll have to fill out some serious holes before it can hold water.

smaller holes than the non existent first stage ACS. 

Anyway, my point was it is mainly from the second stage exhaust. 
Also, the second stage may have had attitude changes too from start transients.

[sittingduck]

Also, the second stage may have had attitude changes too from start transients.

Do you mean to say that the large rotation of the first stage is an illusion caused by the second stage changing its direction of travel?  If not, sorry, but the Earth can be seen rotating into view from the first stage, it is certainly not an illusion. 

SittingDuck - if you can dedicate any more time to this, can you plot out the deduced rotation rate on a time axis?

... and note the ignition time point, and maybe also your data source (since we lose one camera just after rotation starts, right?)

Thanks

I'll give it a shot.  Also yes, if you check the footage, the moment that the first stage is set to begin its rotation, it is lost in the view from second stage.

[Jim]

Do you mean to say that the large rotation of the first stage is an illusion caused by the second stage changing its direction of travel?  If not, sorry, but the Earth can be seen rotating into view from the first stage, it is certainly not an illusion. 

No, I didn't say that.  It would be any motion during the start.

[kevin-rf]

After staging, could LOX venting cause any of these effects? Since you are in Vac, you might not see venting.

[meekGee]

Well, it's a theory.  But you'll have to fill out some serious holes before it can hold water.

smaller holes than the non existent first stage ACS. 

Anyway, my point was it is mainly from the second stage exhaust. 
Also, the second stage may have had attitude changes too from start transients.

What ACS?   All anyone was talking about was a rotation induced by venting or something similar.

If S1 was affected by the exhaust, the change would be gradual, and would be increasing as it rotated more - it would be self reinforcing.  Also, it would start either at ignition time, or at the time of the first small motion, as that would be enough to supposedly catch the jet.

That's why I asked Sitting Duck for the time plot.

Plus, you still need to show that moving the engine bells can actually create enough of a disturbance.  Their moment arms are also awfully small compared the rest of the stage.  Plus, you need to even show that there was such a motion of the gimbals after separation, and that it was extreme - if anything, they should have gone from "actively near center" to "parked on center". 

And another thing.  The main rotation happens at +19 when the stages are pretty far apart.  Care to estimate how wide the exhaust plume is by then?   because it it's hundreds of feet wide (as would be my guess) then S1 is feeling the force of less than 1% of the thrust...  and it is so well aligned that only maybe 1% of that 1% can go towards rotation...  Which doesn't match the very abrupt start of rotation.

[meekGee]

Hey - something new, at least for me.

As I remembered it, the view from S1 got cut off right after S2 disappeared around the edge of the vehicle.

In this video: 

Separation is at 3:50, it goes on for much longer than I remember.

So either I remember it wrong, or there's more than one version.

Can anyone tell me?

[Jim]

What ACS?   All anyone was talking about was a rotation induced by venting or something similar.

Jeesh, you are getting wrapped around the axle.  The point I am making s that the rotation is not intentional

[meekGee]

This is the almost end-of-sequence from S1, after having tumbled over 180 degrees.

There's plenty of time to consider the tumbling timeline.
The views are not synchronized, and I'm looking only at the RHS.
Times are movie times, not embedded time stamp times. (easier to read)

Separation is at 3:47/8
S2 ignition at 3:54, and you can see the plume impinging on S1 immediately, producing a tiny effect, barely perceptible.
Start of rotation is at 4:07, and it is to the opposite effect as the initial tiny effect, just like SittingDuck said. This is after 13 seconds of sitting steady in the plume.
Rotation continues at a clearly constant rate till 4:30 - so for a total of 23 seconds.  This rules out an interaction with the plume - it should have been accelerating the rate of rotation.

***

Just before the sequence ends, the stage seems to stop.  I can't tell if it's freeze frame or if there's a real slowdown.  Can someone rip the video and go frame by frame?  I know people here did it before.  It's between 4:30 and 4:31 in the film.

EDIT:  Looks to me like freeze frame, just before the video switched out.

[meekGee]

What ACS?   All anyone was talking about was a rotation induced by venting or something similar.

Jeesh, you are getting wrapped around the axle.  The point I am making s that the rotation is not intentional

Hey - don't blame me...  You brought up the hypothesis, I'm just showing you it's full of holes.

And intent is not what this was all about.  We were all seeing it happen, it was distinctly different that CRS-1, and we noted that it LOOKED like it was caused by something on S1.  You kept telling us (me) that we're seeing things, but nobody here said they have proof it was intentional.  We said it was caused by an event on S1.

[meekGee]

to refresh my memory, I went back to look at the old videos.

F9 Flight 1:
Stage falls back perfectly aligned till out of view

separation at 3:48, S2 ignition at 3:55, stage remains visibly aligned till 4:07

F9 Flight 2: (COTS Demo 1)
Stage starts rotation immediately after separation, before S2 ignition.

separation at 4:03, rotation at 4:09, S2 ignition at 4:10
This got us talking. Notice rotation before s2 ignition.

F9 Flight 3: (COTS Demo 2)
Night

F9 Flight 4: (CRS-1):
Night

F9 Flight 5: (CRS-2)
Everything discussed above

Separation is at 3:48, S2 ignition at 3:55, rotation at 4:07
Notice rotation after s2 ignition.

[Lars_J]

Tank venting still seems to be the most likely explanation, IMO. (not RCS)

[meekGee]

I agree.

For kicks though, I should find out how much impulse was imparted.
Eyeballing it, the rate of rotation is about 1 RPM.  (SittingDuck - what did you get?)

We can assume conservatively that the vent occurred at the tip of the stage, and extract the minimum impulse from there.

[sittingduck]

For kicks though, I should find out how much impulse was imparted.
Eyeballing it, the rate of rotation is about 1 RPM.  (SittingDuck - what did you get?)

These graphs show the orientation of the first stage over a 44 second time period;  the graphs show X, Y and Z axis orientation in degrees, respectively.  In this case Y is roughly "down" towards Earth.

First stage should make a full 360° rotation about the Y axis in ~94 seconds.

The red X shows stage 2 engine ignition.  The grey area shows when the stage has begun its large rotation.

Please remember that I am not a chart wizard, engineer, mathematician etc. so take all of this with the appropriate amount of salt.

[meekGee]

For sure - but what you've done is distilled numerical data from the visuals, and  this removes an entire layer of interpretation.

[sittingduck]

For sure - but what you've done is distilled numerical data from the visuals, and  this removes an entire layer of interpretation.

Then I have no idea what you wanted me to do in the first place. 

SittingDuck - if you can dedicate any more time to this, can you plot out the deduced rotation rate on a time axis?

... and note the ignition time point, and maybe also your data source (since we lose one camera just after rotation starts,

Like I said before, the deduced rotation rate is roughly 1 per 94 seconds or ~0.64RPM.

[meekGee]

For sure - but what you've done is distilled numerical data from the visuals, and  this removes an entire layer of interpretation.

Then I have no idea what you wanted me to do in the first place. 

No, my bad - I wasn't clear - I was only responding to your disclaimer.   It's all clear and I found it very useful.

[sittingduck]

No, my bad - I wasn't clear - I was only responding to your disclaimer.   It's all clear and I found it very useful.

Ah yes I did not understand.  Thanks, and hopefully some of this information may be useful at some point.

[Galactic Penguin SST]

Worthy bump. 

[manboy]

They're using a special space rated coating on the trunk, apparently they opted to not use it on the Dragon as the thermal requirements aren't there. I've noticed bubbling in the paint in past missions as well. They'll probably swap it out for a better paint on manned Dragon.

NTRS now has some info on the trunk's coating. 

It's called Z-93C55 and was developed by Alion (based in McLean, Virginia). Prior to being used on Dragon it was part of Materials International Space Station Experiments (MISSE)-1 and 2. The coating is an evolution of Z-93P, which was used on a long list of other missions.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130014266_2013014076.pdf

[mlindner]

They're using a special space rated coating on the trunk, apparently they opted to not use it on the Dragon as the thermal requirements aren't there. I've noticed bubbling in the paint in past missions as well. They'll probably swap it out for a better paint on manned Dragon.

NTRS now has some info on the trunk's coating. 

It's called Z-93C55 and was developed by Alion (based in McLean, Virginia). Prior to being used on Dragon it was part of Materials International Space Station Experiments (MISSE)-1 and 2. The coating is an evolution of Z-93P, which was used on a long list of other missions.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130014266_2013014076.pdf

I don't remember where, but I remember reading this before, or at least portions of it. I think in a news article published by the creator.

Edit: Nope it was a NASA news article. http://www.nasa.gov/mission_pages/station/research/news/dragon_coating.html