Author Topic: SpaceX COTS Demo 1 Updates (Read 667778 times)

Comga · « **Reply #1380 on:** 01/05/2011 04:40 pm »

Quote from: ugordan on 01/05/2011 03:29 pm

I speculated a while back that that was done on purpose to induce a tumble to the first stage to aid reentry. I'm thinking it could have been some high pressure gas cartridge in the interstage to give the top of the stage a kick.

Alternatively, I suppose one of the pressurization relief vents could have opened, but it seems like a way too big of a kick for that and we'd see some vapor venting.

A separate gas cartridge system doesn't fit with the SpaceX MO of multi-purposing existing hardware, like using high pressure fuel as the hydraulic fluid and for engine cooling.

The kick does seem too big for just a pressure relief valve opening. The interstage is not massless, what with all those parachutes. (Do we have estimates of their mass?) The force also sems to be an impulse, where an opened valve would keep pushing.

Without anyone profering knowledge about how it is actually done (please, please!) can we speculate on how the lateral force is generated?

MikeAtkinson · « **Reply #1381 on:** 01/05/2011 04:52 pm »

Its hard to tell, but to me it looks like the rotation rate is increasing for about 5 seconds, though the rate of increase seems to be reducing. That would be consistent with pressure release of a steadily decreasing pressure.

Jim · « **Reply #1382 on:** 01/05/2011 04:58 pm »

Quote from: corrodedNut on 01/05/2011 11:33 am

There's only one camera in the interstage, the other one is in the 1st stage engine compartment. The "hoses" are the merlin feedlines, (remember the "octopus": http://forum.nasaspaceflight.com/index.php?topic=17941.msg442587#msg442587 ) the views are from MECO1 and 2; note the recirculating exhaust. The camera switches back and forth between 1st stage engines and interstage, which may explain the "confusion".

Why hasn't anyone commented about the motion in this area at MECO? Seems a little excessive.

Jim · « **Reply #1383 on:** 01/05/2011 05:00 pm »

Quote from: Comga on 01/05/2011 04:40 pm

Quote from: ugordan on 01/05/2011 03:29 pm
I speculated a while back that that was done on purpose to induce a tumble to the first stage to aid reentry. I'm thinking it could have been some high pressure gas cartridge in the interstage to give the top of the stage a kick.

Alternatively, I suppose one of the pressurization relief vents could have opened, but it seems like a way too big of a kick for that and we'd see some vapor venting.

A separate gas cartridge system doesn't fit with the SpaceX MO of multi-purposing existing hardware, like using high pressure fuel as the hydraulic fluid and for engine cooling.

The kick does seem too big for just a pressure relief valve opening. The interstage is not massless, what with all those parachutes. (Do we have estimates of their mass?) The force also sems to be an impulse, where an opened valve would keep pushing.

Without anyone profering knowledge about how it is actually done (please, please!) can we speculate on how the lateral force is generated?

Even though it hasn't ignited, the upperstage engine is venting GOX for the prestart chill down. This could provide the impulse.

There still is the spin down of the engines too

ugordan · « **Reply #1384 on:** 01/05/2011 05:04 pm »

Quote from: Comga on 01/05/2011 04:40 pm

Without anyone profering knowledge about how it is actually done (please, please!) can we speculate on how the lateral force is generated?

Well, you heard my theory. I disagree about that not being their modus operandi. Why not? All Falcon upper stages currently use cold gas thrusters so this wouldn't be unprecedented. It's not as if they'd have to develop a new thruster solely for inducing tumble.

Agree on the impulsive event appearance - that's why this seems like a quick discharge as opposed to some tank relief venting to me.

ugordan · « **Reply #1385 on:** 01/05/2011 05:11 pm »

Quote from: Jim on 01/05/2011 05:00 pm

Even though it hasn't ignited, the upperstage engine is venting GOX for the prestart chill down. This could provide the impulse.

If that was the case, I'd also expect attitude disturbances on the 2nd stage. I don't see any. It's also noticeable how the tumble onset is pretty abrupt, after the 2nd stage is well clear of the 1st stage.

This sort of venting looks pretty similar to what we see with Centaur after separation and it doesn't affect the top of the booster stage even remotely similarly. One would also have to come up with a reason why flight #1 didn't experience this as well.

Lars_J · « **Reply #1386 on:** 01/05/2011 05:16 pm »

Quote from: Jim on 01/05/2011 04:58 pm

Quote from: corrodedNut on 01/05/2011 11:33 am
There's only one camera in the interstage, the other one is in the 1st stage engine compartment. The "hoses" are the merlin feedlines, (remember the "octopus": http://forum.nasaspaceflight.com/index.php?topic=17941.msg442587#msg442587 ) the views are from MECO1 and 2; note the recirculating exhaust. The camera switches back and forth between 1st stage engines and interstage, which may explain the "confusion".

Why hasn't anyone commented about the motion in this area at MECO? Seems a little excessive.

Is there any footage from another LV taken from inside the thrust structure at MECO that we can compare with? I suppose some material flex is to expected, going from 2-3Gs (?) to free-fall.

ugordan · « **Reply #1387 on:** 01/05/2011 05:18 pm »

More like 4 or 5 Gs near MECO2.

ugordan · « **Reply #1388 on:** 01/05/2011 06:08 pm »

Quote from: ugordan on 01/05/2011 05:04 pm

Agree on the impulsive event appearance - that's why this seems like a quick discharge as opposed to some tank relief venting to me.

FWIW, based on 2nd stage camera location and the direction of the impulse, I'd say the hole in the interstage marked in this image is the most plausible candidate. Which seems to be the 1st stage LOX tank vent at least.

Jim · « **Reply #1389 on:** 01/05/2011 06:25 pm »

Quote from: ugordan on 01/05/2011 05:11 pm

1. If that was the case, I'd also expect attitude disturbances on the 2nd stage. I don't see any.

2. It's also noticeable how the tumble onset is pretty abrupt, after the 2nd stage is well clear of the 1st stage.

3. This sort of venting looks pretty similar to what we see with Centaur after separation and it doesn't affect the top of the booster stage even remotely similarly.

4. One would also have to come up with a reason why flight #1 didn't experience this as well.

1. 2nd stage is under 3 axis thruster control

2. I didn't say the venting was occurring during the beginning of separation. It could have been the initial "burp"

3. Centaur may vent differently

4. Not every artifact is present every mission

jabe · « **Reply #1390 on:** 01/05/2011 06:46 pm »

For second stage re-ignite..would they need a ullage motor?
jb

ugordan · « **Reply #1391 on:** 01/05/2011 06:48 pm »

ACS cold gas thrusters would settle the propellants.

Comga · « **Reply #1392 on:** 01/05/2011 07:51 pm »

Quote from: ugordan on 01/05/2011 06:08 pm

Quote from: ugordan on 01/05/2011 05:04 pm
Agree on the impulsive event appearance - that's why this seems like a quick discharge as opposed to some tank relief venting to me.

FWIW, based on 2nd stage camera location and the direction of the impulse, I'd say the hole in the interstage marked in this image is the most plausible candidate. Which seems to be the 1st stage LOX tank vent at least.

It could be.

However, that hole seems to be too far down the stage although it does appear to be in the right place rotation-wise. The umbilical and the corresponding hole in the interstage (seen a few frames earlier) are less than 90 degrees apart. (blue arrows)

I think we can see the Falcon logo in the video. (red arrows) The port seems to be above the logo. (green arrows) not below it (your red arrow.)

A more throrough analysis could scale the lengths to determine how far down the rocket that hole in the video sits.

If a vent valve was popped on something with limited volume, it could give a quickly decaying impulse like we think we see. Even if SpaceX had to add a valve that wouldn't be that big a deal. Maybe what we see in the video is the exit of a bell designed to get more thrust in that direction from the cold gas.

Comga · « **Reply #1393 on:** 01/05/2011 07:52 pm »

(Image attached this time....)

Edit: I just went back to look for the video with the interior views of hte interstage, and can't seem to find it in the SpaceX.com video gallery. Am I missing something obvious or has it been removed?

meekGee · « **Reply #1394 on:** 01/05/2011 08:26 pm »

Yes, the split screen is gone.

But, take a look at the attached picture, and play with the video around 1:35.

The first stage is clearly intercepting some of the otherwise invisible plume, and it becomes visible inside of the interstage.

Even though they are still aligned, even a small deviation can cause the tumbling under this assumption.

Comga · « **Reply #1395 on:** 01/05/2011 08:42 pm »

Did anyone download that split screen video?

jabe · « **Reply #1396 on:** 01/05/2011 10:19 pm »

Quote from: Comga on 01/05/2011 08:42 pm

Did anyone download that split screen video?

I have it a work..shhhh....

Chris-A · « **Reply #1397 on:** 01/05/2011 10:40 pm »

Someone need screenshots from the video?
http://img152.imageshack.us/gal.php?g=spacex1.jpg

Edit, I have both videos, I didn't notice any out-gassing on the interstage.

meekGee · « **Reply #1398 on:** 01/05/2011 11:10 pm »

Actually, even though the interstage is definitely catching some of the exhaust plume, the rolling definitely starts before the second stage lights up.

Here's a question for someone who might know - when the 9 Merlins shut down, what happens to the angular momentum stored in the pumps? Do they spin on regular bearings or something fancier like air bearings? Any chance some knows how much the rotors weigh and how fast they are spinning, and most importantly - in what direction they are mounted?

Comga · « **Reply #1399 on:** 01/05/2011 11:27 pm »

Quote from: meekGee on 01/05/2011 11:10 pm

Actually, even though the interstage is definitely catching some of the exhaust plume, the rolling definitely starts before the second stage lights up.

Here's a question for someone who might know - when the 9 Merlins shut down, what happens to the angular momentum stored in the pumps? Do they spin on regular bearings or something fancier like air bearings? Any chance some knows how much the rotors weigh and how fast they are spinning, and most importantly - in what direction they are mounted?

I agree with your first statement, if not said already.

Here are two photos of an early Merlin 1, before it had a letter appended to the name, from December 2003 IIRC. The axis of the turbopump, here at the top, appears to be parallel to the thrust vector.

If the turbines all stopped, the stage would probably rotate. It's also hard to imagine them all (or 7 of them) stopping instantaneously and simultaneously.