FAILURE: SpaceX Falcon I Launch III - August 2

[Analyst]

Good move to release the video.

Analyst

[Firehawk153]

I love the new farther off perspective of the first few seconds of launch...very impressive. 

Not to mention that the trees are still standing.

[JWag]

The video is excellent. I am happy to see that spacex released it. Allot of companies never would have.

Indeed!

I wonder what regression testing of rocket guidance software looks like...

[Lee Jay]

I'm glad they released this.  There's actually a lot of the flight past where the webcast stopped.

I'm a little unclear as to what happened.  The second stage ignited for about 1 frame of the video, and then the video stopped.  Was the second stage engine damaged by the recontact, and it therefore burned improperly thus causing the tumble or did something else happen as a result of the recontact?

[Paul Adams]

Congrats on the brave move to release the video and explination of the mishap.

Elon and the team deserve the success they will soon achieve.

Paul

[DaveS]

I'm glad they released this.  There's actually a lot of the flight past where the webcast stopped.

I'm a little unclear as to what happened.  The second stage ignited for about 1 frame of the video, and then the video stopped.  Was the second stage engine damaged by the recontact, and it therefore burned improperly thus causing the tumble or did something else happen as a result of the recontact?

If look closely when the fairing is jettisoned, you can see that the second stage is a violent tumble, so I guess when the Kestrel ignited inside the interstage adapter, it caused the stages to start tumbling rapidly, which led to LOS with Kwaj as the antenna(s) wasn't pointing in correct direction anymore. I guess they were fortunate to recover the signal right before payload fairing unlatch and jettison.

[Lee Jay]

I know, Dave, I'm wondering what caused the tumble.  Perhaps the engine nozzle was damaged by the recontact, or...something.

[kraisee]

Just a thought, but if S1-S2 separation delay wasn't long enough, I hope they are allowing plenty of time after S2 MECO before Payload Separation too.

Fixing this problem here and not fixing any similar issues there would be a really bad mistake to make.

Ross.

[Damon Hill]

Just a thought, but if S1-S2 separation delay wasn't long enough, I hope they are allowing plenty of time after S2 MECO before Payload Separation too.

The Kestrel engine is a much simpler pressure-fed design and should shut down much more positively.  I recall that there is a coast period following shutdown, and the three-axis RCS will maintain a stable attitude for payload separation.  I think Flight 2 did successfully demonstrate a payload separation despite the tumbling.

Though maybe the guidance package should be monitoring acceleration rates before separation phases to ensure things have settled down?

[dunderwood]

Correct me if I'm wrong, but I thought I remembered seeing 10 seconds on timelines between second stage cutoff and payload deployment.

[renclod]

Thanks to Space Exploration for the video. Dramatic !

[Damon Hill]

Fire in the hole!  (oops, that's not supposed to happen...)

[HMXHMX]

Just a thought, but if S1-S2 separation delay wasn't long enough, I hope they are allowing plenty of time after S2 MECO before Payload Separation too.

The Kestrel engine is a much simpler pressure-fed design and should shut down much more positively.  I recall that there is a coast period following shutdown, and the three-axis RCS will maintain a stable attitude for payload separation.  I think Flight 2 did successfully demonstrate a payload separation despite the tumbling.

The impulse is due to trapped propellant volumes in injectors and cooling chambers. Even pressure fed engines will have the problem.

One reason we adopted the rather difficult to develop face-shutoff for our pintle engine (at AirLaunch) was to provide a much cleaner shutdown impulse than upstream valves.  We get very crisp, fractional second shutdowns with no residual thrust.  I suggested this to Elon five years ago but he didn't want to adopt it.  It also makes reuse easier, since after recovery, you don't have to worry about sea water getting into the engine upstream of the injector.  The down side is development is definitely more difficult.

During the second flight, the vehicle was tumbling end over end at quite a rate.  In that case, payload sep would be clean – the payload was on the end of a rotating body and was flung off by centrifugal force.  I don't believe that they ever regained three axis control of Flight 2's second stage, but I could be wrong.

[aero313]

Just a thought, but if S1-S2 separation delay wasn't long enough, I hope they are allowing plenty of time after S2 MECO before Payload Separation too.

Fixing this problem here and not fixing any similar issues there would be a really bad mistake to make.

Ross.

During ascent you want the staging delay to be as short as possible to avoid gravity losses.  Once the vehicle is in orbit, there's no such constraint.  Typically launch vehicles will wait several minutes to let the engine finish outgassing before payload sep.

[aero313]

The video is excellent. I am happy to see that spacex released it. Allot of companies never would have.

Usually the ability to release video and other flight information is controlled by the customer who paid for the launch, not necessarily the company that built the launcher.

[mheney]

Is the roll oscillation I'm seeing usual for a launch?  When you wach the video, the vehicle looks like it rolls clockwise for about a second, then corrects back to over the next second, then rolls, then corrects ...  I can see that causing a few challenges during flight...

[iamlucky13]

Mheney, are you talking about the rolling back and forth and slight pitching that grows slowly throughout the 1st stage burn as the rocket gets lighter?

That was noticed during the live launch coverage and several other people commented on it. No it's not normal (at least for other rockets). Speculation seems to be pretty consistent that it's torque from fuel being spun through the cooling channels on the nozzle. The control system kept it from getting out of hand, but hopefully SpaceX will take a look at improving the rocket's ability to deal with it smoothly.

What a great video, however. I didn't expect to be treated to a near HD shot of liftoff. It was almost eery how smoothly the 1st stage essentially "relocked" against the second stage.

Am I correct that there was a second camera inside the payload fairing that provided coverage for that separation event? It seems the down-facing camera must-have been fried by the 2nd stage ignition.

Also, why does the exhaust continually get darker as the rocket ascends? Are they changing the mixture to increase fuel burn-up?

[henryhallam]

I guess when the Kestrel ignited inside the interstage adapter, it caused the stages to start tumbling rapidly, which led to LOS with Kwaj as the antenna(s) wasn't pointing in correct direction anymore. I guess they were fortunate to recover the signal right before payload fairing unlatch and jettison.

I call shenanigans - the odds of losing signal immediately then, and then fortuitously recovering it for just a second exactly when fairing sep occurred are pretty slim.  I bed they have video throughout, but aren't releasing the rest of it, very understandably.  Unlike the 30 seconds leading up to 2nd stage ignition, the post-ignition tumbling video would be less technically interesting and more morbidly fascinating.

Also, why does the exhaust continually get darker as the rocket ascends? Are they changing the mixture to increase fuel burn-up?

SWAG: The mixture ratio may or may not change, but it tends to be fuel-rich, so some fuel is remaining in the exhaust.  This burns in air, when there's air, and not when there's not.

[William Barton]

I remember seeing a similar back and forth roll from some early recovered film of space launches, especially the V-2 footage that used to be in the opening of "The Twentieth Century" TV program from the 1950s (a fond memory from my childhood, alongside "Victory at Sea"). It made it look like the V-2 didn't have roll control. Which leads to a question for the rocket scientists: How good was roll control on the V-2 and Redstone, where guidance control was from graphite vanes in the rocket exhaust?

[iamlucky13]

Also, why does the exhaust continually get darker as the rocket ascends? Are they changing the mixture to increase fuel burn-up?

SWAG: The mixture ratio may or may not change, but it tends to be fuel-rich, so some fuel is remaining in the exhaust.  This burns in air, when there's air, and not when there's not.

Ahhh! Makes perfect sense.