Falcon 1 Flight 3 Launch Thread

[simonpro]

It's more likely that the down stream terminated upon destruction of the vehicle. Rather than SpaceX actually editing the video.

Nope, SpaceX edited the video. The simplest way to tell this is because the last 2 or 3 seconds show fairing separation, not booster sep.

Surely. SURELY they tested the new first stage motor, and noticed residual burning after cut off. I'm no part of SpaceX, and don't claim to know anything more than their engineers do, but it seems that this issue should have been observed and fixed on the ground way before the launch.

I mean, any ground fire test of the new first stage engine would have shown residual burning, right? How this couldn't have been accounted for in the staging timing is beyond me.

Yes, the residual burn was visible in the ground test. There was a video of one of their tests published a while back, and that clearly showed this burning. A couple of my colleagues (who know more about engines than I) even suggested it'd be a problem, as did many others. None of whom worked at SpaceX, however.

 

[to be]

It might have destroyed or otherwise obstructed the camera though, which would have cut all the video until the fairing separated to give another camera a view.

 

[GregBurch]

Yes, the residual burn was visible in the ground test. There was a video of one of their tests published a while back, and that clearly showed this burning. A couple of my colleagues (who know more about engines than I) even suggested it'd be a problem, as did many others.

I have to say that if that is the problem, and your buddies spotted it, the story is shocking.

Questions: has it been stated by SpaceX that it was residual burning/thrust from the 1st stage that caused the problem? Is it clear now that there really was a good sep, and the only cause was the "rear-end collision?" If so, I wonder if anyone's worked up an estimate of what the the impact velocity between the two stages was ...

 

[Notebook]

It might have destroyed or otherwise obstructed the camera though, which would have cut all the video until the fairing separated to give another camera a view.

Looking at previous videos, I got the impression that there is just one camera/video feed, and some form of mirror/lens/solenoid arrangement to give the view of the fairing seperation, then returning to the aft facing view?

Obviously I don't know, but I think it would be cheaper/lighter/simpler than having two cameras/video feeds. You lose the advantage of having two simultaneous images though.

N.

 

[Urwumpe]

I have to say that if that is the problem, and your buddies spotted it, the story is shocking.

It is not really shocking, it is a typical behavior of many rocket engines (for example the F-1 engine had similar residual burning after cut-off).

Also, you have to remember that you are talking about powerful turbo-machinery. You can't just cut the thrust instantly and you have to ensure a fuel rich cut-off, otherwise, the oxygen can ignite hot surfaces.

The second flight had already problems with the engine controller software, I would not be surprised if similar problems happened in this flight. For example, if a valve closes in the wrong fraction of a second, the turbine can for example over spin and have a lower pressure drop, letting the exhaust pipe create more thrust.

And you will not even notice it in ground testing - the exhaust pipe should have so little overpressure that it's thrust during cut-off can even be zero on the ground and a few dozen N thrust in vacuum.

But that is just one behavior you have to keep in mind when you design the staging sequence.

Questions: has it been stated by SpaceX that it was residual burning/thrust from the 1st stage that caused the problem? Is it clear now that there really was a good sep, and the only cause was the "rear-end collision?" If so, I wonder if anyone's worked up an estimate of what the the impact velocity between the two stages was ...

I can't watch the stream as my bandwidth is too low, but as the first stage is almost dry, even purging the engine line should be powerful enough to give it a few cm/s speed, the gas generator exhaust even more.

 

[Quick_Nick]

Questions: has it been stated by SpaceX that it was residual burning/thrust from the 1st stage that caused the problem? Is it clear now that there really was a good sep, and the only cause was the "rear-end collision?"

http://spacex.com/updates.php

The problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine, as compared to the prior flight that used our old Merlin 1A ablatively cooled engine.
...
Unfortunately, the engine chamber pressure is so low for this transient thrust -- only about 10 psi -- that it barely registered on our ground test stand in Texas where ambient pressure is 14.5 psi. However, in vacuum that 10 psi chamber pressure produced enough thrust to cause the first stage to recontact the second stage.

 

[GregBurch]

It is not really shocking, it is a typical behavior of many rocket engines (for example the F-1 engine had similar residual burning after cut-off).

What I meant was that it was shocking that this issue wasn't taken into account ...

I can't watch the stream as my bandwidth is too low, but as the first stage is almost dry, even purging the engine line should be powerful enough to give it a few cm/s speed, the gas generator exhaust even more.

I see: almost empty 1st stage + a little residual thrust from the 1st stage engine = ramming speed ...

 

[simonpro]

I have to say that if that is the problem, and your buddies spotted it, the story is shocking.

One of them mentioned it in an email containing a link to the engine test. His exact words were "check the blast after shutdown..bet that is giving them some seperation headaches!"

Questions: has it been stated by SpaceX that it was residual burning/thrust from the 1st stage that caused the problem? Is it clear now that there really was a good sep, and the only cause was the "rear-end collision?" If so, I wonder if anyone's worked up an estimate of what the the impact velocity between the two stages was ...

The impact velocity was on the order of 0.8-1m/s. It wasn't the collision itself that was the major problem though, it was the "fire in the hole" afterwards when the second stage ignited. From the rumors I've heard it tore the nozzle to hell and completely saturated the guidance system (which obviously couldn't control a rocket with a broken nozzle).

 

[Urwumpe]

I see: almost empty 1st stage + a little residual thrust from the 1st stage engine = ramming speed ...

Yes - it is spaceflight, you will (likely not) be surprised how little speed is needed for damaging a rocket.

10 tons at 20 cm/s has the same effect as a car at 2 m/s / 7.2 km/h / walking speed.

 

[silent_protagonist]

Well, you need to be careful adding multiple redundant 'fixes'. You don't want to start adding things that add complexity, that's a great way to introduce bugs. If there is one simple thing they can do to fix it, that is the best option. If it fails, then try one more thing.

That's a good point. Lol, why does rocket science always have to be so complicated?:lol:

 

[Andy44]

The impact velocity was on the order of 0.8-1m/s. It wasn't the collision itself that was the major problem though, it was the "fire in the hole" afterwards when the second stage ignited. From the rumors I've heard it tore the nozzle to hell and completely saturated the guidance system (which obviously couldn't control a rocket with a broken nozzle).

That's what I read, as well. The second stage nozzle ignited while cupped inside the interstage and the plasma blowback tore it all up.

 

[GregBurch]

That's what I read, as well. The second stage nozzle ignited while cupped inside the interstage and the plasma blowback tore it all up.

I remember back when I was a kid they had warning labels on fireworks -- they went something like:

• Lite fuse and GET AWAY

Good advice for the would-be rocketeer. So the take-away lesson here is:

1. Separate clean.
2. Then light the candle.

OK. I think I got it ....

 

[Urwumpe]

Tell that the Russians. They first light the candle (a bit) and then separate clean.

Of course, this means the first stage is not reusable and the second stage needs more thrust for good separation.

 

[Andy44]

The Titan rockets also ignited Russian-style, IIRC. Titan interstages had vent holes similar to Russian ones.

 

[GregBurch]

Point taken. But that only works if you know what you're doing

 

[Notebook]

Going slightly off the main topic, here's some graphs of the seperation characteristics of the first/second stages of the Europa rocket.

http://s89.photobucket.com/albums/k207/Notebook_04/?action=view&current=File0011.jpg

The residual thrust of the first stage isn't much less than the stage seperation motor at seperation.

Anyone know what the ABS signal at time zero might be?

N.

 

[simonpro]

The Titan rockets also ignited Russian-style, IIRC. Titan interstages had vent holes similar to Russian ones.

Falcon-1 seemed to create it's own ventholes, mind you

(edit) Sorry, couldn't resist.

 

[Native Son]

Falcon-1 seemed to create it's own ventholes, mind you

(edit) Sorry, couldn't resist.

And rightfully so! :rofl:

 

[C3PO]

Do you guys think we'll ever see the missing parts of that launch? It would be very interesting to see how it behaved after staging.
The rate of rotation was crazy during fairing sep.

 

[Lunar_Lander]

By the way, the problem of residual thrust and stages colliding with each other seems not to be new. The Japanese Lambda had two occasions, where the third stage collided with the fourth stage due to residual thrust.

Source: http://www.isas.ac.jp/e/japan_s_history/detail/challenge.shtml