LIVE: SpaceX - Falcon I (Mk.II) NET March 20 (Attempt 2)

[jabe]

seems spacvex added an update..
http://www.spacex.com/updates.php#demoflight_2_prelim_review_2
but it doesn't say much

[clongton]

jabe - 9/4/2007  11:00 AM

seems spacvex added an update..
http://www.spacex.com/updates.php#demoflight_2_prelim_review_2
but it doesn't say much

Just letting us know he hasnt forgotten us.
Thanks Elon

[Comga]

jabe - 9/4/2007  9:00 AM
seems spacvex added an update..but it doesn't say much

What he said is almost as short as your link  

Posted April 8, 2007
We are still reviewing data, so the full subsystem analysis is not quite ready yet.  I should be able to post that update within approximately two weeks.
--Elon--

For a group with such remarkable engineering accomplishments, their schedule veracity is slim.  Ten days after saying they would have more in a week, they say they will have more in two weeks.    Oh well,  at least we eventually get the info.

[clongton]

Dont complain. When was the last time Lockmart or Boeing went out of their way to keep us in the loop? Granted, they have a LOT more going on, but they also have Public Information Offices. Elon IS the PIO.

[Comga]

There is something truly interesting in the initial report that I haven't seen discussed.  

In the video on their website the cutoff time is T+0:05:01, although the live broadcast seemed to go on for a few more seconds.  At that time the yaw-pitch oscillation is pretty strong and is begining to generate significant roll.  (~25 degrees cumulative)

However, the time stamps on the website photos are well after this.  The glowing nozzle photo is time stamed T+7:17.   Could this image really have been captured more than two minutes later than what is shown in the video?  Could the second stage have continued to fire for two minutes with such extreme perturbations?

The image does seem to be degraded by a strong roll  (It looks like NTSC interlaced video.)

The image time stamped T+8:12 with the engine shut down and cool has even more roll degradation.  However, the image time stamped T+10:10 does not.  It appears that the roll control system was not only functioning but sufficiently strong to stop the roll within two minutes.  That in itself is impressive.  

[axel321]

Hi there,
spent most of the long easter weekend to read this thread. It's cool to find so many experts here discussing spacex in public. Thank you for that!

@Comga: yes, spacex did say they recovered almost all of the video data stream after the web cast broke. Yes, judging from the interlace effects, the tumbling got pretty bad. But in the last frame at 10:10 it looks almost ok again. So I still hope the full video will be published to demonstrate robustness of the control system. It could help to make the so much discussed 95% success more obvious (hint, hint).

I'm still not sure whether the webcast was turned off or broke because of signal problems. For the cameras on Omelek bad signal didn't cause webcast termination. But those seem to be transmitted by analog signal and the onboard cam probably used a digital channel. So maybe it made a difference. Also having ten more seconds on one of the youtube videos might indicate that part of the webcast terminated later than others. This would be consistent with the "breaking due to loss of signal" hypothesis. (If some insider with access to the video stream would have broadcasted it, then why not more of it?)

The last frame I got from the webcast was at the beginning of T+5:05. Anyone got more or less?

By the way: the frames displayed on the spacex update page have the time displayed differently, so they are not from the webcast but from an earlier video processing stage.

Did you note: the freeze frame labeled T+3:09 has a different time assigned in the webcast. Maybe the label was made manually and should have been T+3:19? Or is it a consequence of these strange transmission problems when the camera is switched to upwards (another camera, I guess, with sync problems when switching?) and back to downwards again?

Finally two question to the experts here:

1) if the parachutes of stage 1 are put under the nozzle of stage 2, wouldn't ignition of second stage damage the parachutes? Maybe part of the turning motion before ignition is on purpose?

2) is there really a lot of free space in the tanks of stage 2 for an initial slosh? If yes, what would be a typical slosh frequency? (I'm asking because during the re-contact of the stages, stage 2 seems to stop its side motion and restarts a considerable time after final separation. Would this be consistent with slosh?)

[Edit] thinking about 2) again, frequency might be the wrong question, because it happens in free fall. So hardware rotation is stopped by re-contact but fuel continues to rotate. Then fuel transfers rotation back to hardware. Hmm, is this a plausible answer? To me it still looks like the re-contact can't have transferred much energy between stages, because the nozzle is so wobbly...

[Comga]

Axel321: Do you have a link to that slightly longer YouTube video?

And from everything I have read, the rotation rate of the first stage was not only unanticipated, but it was a surprise.  Musk says it was five times the maximum anticipated (2.5 deg/sec instead of 0.5) and they intend to correct it on the next flight by a more gradual reduction of the thrust.  There is no hint that they are worried about the impingement of the second stage rocket plume on the still-furled first stage parachutes.

[kevin-rf]

Comga - 9/4/2007  1:57 PM

Axel321: Do you have a link to that slightly longer YouTube video?

It has been posted in the tread several times. A quick search of youtube using "falcon I" turns up several. This one has the extra few seconds and a full revoluton of the second stage.

http://youtube.com/watch?v=7LpKCVrUJNg&mode=related&search=

[axel321]

The link was posted on this thread a few days after launch. Searching... searching...

And from everything I have read

Yes, I read that on the spacex update page, which is also referenced and quoted frequently on this thread.
(Hint: you might want to read the rest of the thread, so we can talk about new things.   )

[Chris-A]

Posted April 8, 2007

We are still reviewing data, so the full subsystem analysis is not quite ready yet.  I should be able to post that update within approximately two weeks.

--Elon--

Mr. Musk has posted a small update on the flight analysis, from what I have herd from Elon they has a terabyte (1024GB) of data to look over.

EDIT: Ops. I didn’t see the other post

[Comga]

axel321 - 9/4/2007  12:46 PM
......
Yes, judging from the interlace effects, the tumbling got pretty bad. But in the last frame at 10:10 it looks almost ok again. So I still hope the full video will be published to demonstrate robustness of the control system. It could help to make the so much discussed 95% success more obvious (hint, hint).
....

I agree.  The posted image with the time stamp of 10:10 seems to show the engine spewing fuel and/or oxidizer, and holding the original attitude without significant roll rate.  It looks as if the system could have restarted the second stage, for which it has the capability, and gotten at least  some of the remaining velocity needed for orbit.   So close and yet so far away.

I wonder they will take the hint and if we will have this confirmed.

[Jim]

The fact that they have images past T+5:15 means they cut of the internet transmission much like Spacelaunch

There is a difference between control during engine burn and coast.  There is no 'robustness" of the control system.  The TVC system is unstable.  Just because RCS system was able to damp out excursions after shutdown doesn't help much if there is a velocity shortfall.  Sort of like being able to steer going down a steep hill without brakes

[JIS]

Jim - 10/4/2007  11:32 AM

There is a difference between control during engine burn and coast.  There is no 'robustness" of the control system.  The TVC system is unstable.  Just because RCS system was able to damp out excursions after shutdown doesn't help much if there is a velocity shortfall.  Sort of like being able to steer going down a steep hill without brakes

Everybody sow how unstable Pixel was during initial Armadillo tests and how it was fixed later. If this is their only issue than it can be "easily" fixed.
SpaceX doesn't have such rigid procedures as NASA or old.space have. It makes system more likely to fail but easier to fix. That's the price new.space must pay.
I still think that the most serious Falcon flaws are those nobody knows about or those beeing neglected. As Falcon 1 is really cheap and marginal part of SpaceX business I'm more worried about Falcon 9 which needs reliable Falcon 1 first.

[Jim]

JIS - 10/4/2007  7:48 AM

1.  Everybody sow how unstable Pixel was during initial Armadillo tests and how it was fixed later. If this is their only issue than it can be "easily" fixed.

2. SpaceX doesn't have such rigid procedures as NASA or old.space have. It makes system more likely to fail but easier to fix. That's the price new.space must pay.
QUOTE]
1.  How so?  Is the cause known?  It is just a software change or are there hardware issues?  It will take flight tests to verify any fix.  

2.  Why is it easier to fix?

[meiza]

Armadillo builds and tries new stuff often because
1) their individual designs are cheap
and they test often because
2) they have a reusable design

SpaceX really has neither of these (somewhat cheaper than real launchers tho). Of course now Jim and others will chime in that reusability is useless.

[JIS]

Jim - 10/4/2007  1:21 PM

2.  Why is it easier to fix?

From what I see it looks like Space X doesn't have all those procedures and company culture in place as NASA and old.space have. It means that there is higher likelyhood of problems but it is faster and cheaper to fix them.
From the past SpaceX progress it looks like when they encounter problem (launch pad, merlin, etc.) they find solution and fix it fairly simply and quickly. After all Falcon 1 is relativelly cheap and simple and it's 2nd stage is even more simple and cheap.
Armadillo is an extreme - no procedures, very frequent testing. Nasa is another extreme. SpaceX is somewhere between so I can see some logic in Musk statement that they are essentially happy with Falcon 1 and willing to take a quick fix to fly again. With upgraded flight control and slosh baffles they shouldn't experience the same kind of problem again. It happend with all their previous problems during last 4 years. They overlooked loads of bugs, but once they indentified them they were very successful to fix them. It's simply their way of doing things.

That's similar way Russians took with Soyuz. With Falcon 1 this could work but I'm concerned about Falcon 9 which shouldn't fail so often.
To be honest I'm not expecting Space X can perform their next launch whithout any problems.

[axel321]

Just because RCS system was able to damp out excursions after shutdown doesn't help much

Well, I'm no rocket scientist, nor a control expert, but I did a bit of robotics and from that I learned that bad control laws usually lead to a crash. If the control laws used would have been real faulty, like stuck in position "turn left", then the main engine would have put more and more rotational energy into the second stage. As the main engine has a lot more push then the cold gas thrusters, the latter wouldn't be able to compensate in the end, would they?

Unless the second stage was flying in full circles and Elon Musk showed us only those two pictures where it accidentally looked ok, then the control is basically ok, but needs a bit of tuning.

[kevin-rf]

axel321 - 10/4/2007  4:58 PM

Just because RCS system was able to damp out excursions after shutdown doesn't help much

Well, I'm no rocket scientist, nor a control expert, but I did a bit of robotics and from that I learned that bad control laws usually lead to a crash. If the control laws used would have been real faulty, like stuck in position "turn left", then the main engine would have put more and more rotational energy into the second stage. As the main engine has a lot more push then the cold gas thrusters, the latter wouldn't be able to compensate in the end, would they?

Unless the second stage was flying in full circles and Elon Musk showed us only those two pictures where it accidentally looked ok, then the control is basically ok, but needs a bit of tuning.

The second stage did a full roll in the extra 10 seconds on the YouTube video. SpaceX was able to and obvious did pick images that where all at the same point in the roll. Cherry picking the images mitigates the raised eyebrows from looking at rotated images. That is called media spin. What they could not do was hide the rate of roll evident in the fuzzy horizon because of the interlaced nature of the camera. Anyone one want to bet the next camera they fly will not be interlaced? SpaceX has said through Mr. Musk that the contact during staging was more than the control system could handle, and it was more than was predicted.

btw. The main engine was not the cause of the roll. It was the sloshing LOX in the tank and lack of baffles. The cold gas thrusters are used for roll control because a single main engine (That lacks a turbine exhaust) can not roll the vehicle.

[Avron]

kevin-rf - 10/4/2007  10:24 PM


btw. The main engine was not the cause of the roll. It was the sloshing LOX in the tank and lack of baffles. The cold gas thrusters are used for roll control because a single main engine (That lacks a turbine exhaust) can not roll the vehicle.

Not lack of baffles, just not large enough for the staging transients/slosh..

I think if you try and correct a Yaw/pitch cyclic motion, you may end up with roll, without the engine providing any roll torque to the vehicle.. "gyroscopic precession " and all that..

[meiza]

The stage did not only roll in the youtube clip, but it pitched/yawed so that the nozzle was pointing in the completely wrong direction, say, 90 degrees to the flight path. Everyone can see this for themself.