Author Topic: Falcon 1 - Post Failure thread (Read 134925 times)

Delta Manager · « **Reply #160 on:** 03/26/2006 02:53 am »

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Damon Hill - 25/3/2006 6:21 PM

Entrained exhaust in the aft section during launch is a common
occurance; the Delta IV and some other rockets have an aft fairing to protect
the engine hardware.

Image to compare...

lmike · « **Reply #161 on:** 03/26/2006 02:58 am »

Indeed... Although, I though "the fireball" was specifically due to the LH2 and the exhaust duct system used for Delta4. Any similar images with Kerosene engines?

hyper_snyper · « **Reply #162 on:** 03/26/2006 03:00 am »

The Merlin engine on the Falcon is exposed while the RS-68s on the Delta IV Heavy in the image above are not. I think SpaceX should at least contemplate covering the engine, especially with their gas-generator exhaust so close to the piping.

lmike · « **Reply #163 on:** 03/26/2006 03:02 am »

Actually from the onboard SpaceX video it does look like a rapture in plumbing (the flameout about 90 deg sideways) (if the nozzle didn't get burned through)

Super George · « **Reply #164 on:** 03/26/2006 03:14 am »

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lmike - 25/3/2006 9:02 PM

Actually from the onboard SpaceX video it does look like a rapture in plumbing (the flameout about 90 deg sideways) (if the nozzle didn't get burned through)

From the video, it's got the appearance of a rupture.

Shuttle Man · « **Reply #165 on:** 03/26/2006 03:27 am »

Well, we don't know for sure yet, but the general feeling amoungst people I've spoken to today is the potential to look at moving to a regen-cooled engine. Ablative was a brave move.

Damon Hill · « **Reply #166 on:** 03/26/2006 04:55 am »

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Shuttle Man - 25/3/2006 9:27 PM

Well, we don't know for sure yet, but the general feeling amoungst people I've spoken to today is the potential to look at moving to a regen-cooled engine. Ablative was a brave move.

Doesn't appear to be a factor in this launch, but Spacex apparently hasn't had the
best results. It'd be cheaper than tube bundle, which is time/labor intensive to fabricate.
Milled wall is gaining popularity--the Russians use that technique commonly now.
Or it might be a hybrid with an ablative liner downstream of the throat as with the
RS-68.

I think they weren't completely satisfied with the pintle injector, but I can understand
why they wanted to go that route; it's about as simple as it gets. Merlin doesn't need to
be fancy, just cheap and reliable. Emphasis on reliable, I'm guessing.

Anyway, it'll be fun to watch and guess their next move.

How is axis roll controlled; is the turbopump exhaust duct steerable?

Nick L. · « **Reply #167 on:** 03/26/2006 05:02 am »

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Damon Hill - 25/3/2006 10:55 PM

How is axis roll controlled; is the turbopump exhaust duct steerable?

I don't think the turbopump exhaust is steerable, I don't see any actuators on the exhaust.

lmike · « **Reply #168 on:** 03/26/2006 06:08 am »

Looking at http://upload.wikimedia.org/wikipedia/commons/c/ca/SpaceX_Merlin_engine.gif One can only see the engine gimbal actuators (2; upper left, and one behind), the 'flameout' seems to have occured at one of the propellant feeds up at the base. The exhaust seems to be fixed firm (relative to the chamber/nozzle).

edstrick · « **Reply #169 on:** 03/26/2006 06:18 am »

A few comments on discussion since I posted the idea the blanket may have THWAPPED something in the engine compartment.

This is a good example of a plausible cause and effect probably having nothing to do with the failure. It's indeed possible that blasted up debris may have hit something one or two seconds after liftoff. That's especially possible since engine burps on the pad don't have the rocket above the pad with the plume spreading out and hitting different things that it does on teh pad. I hope they have multiple angle camera data on the pad and base of the rocket.

If a debris strike isn't the problem, then at a purely arm-waving over a glass of virtual-beer argument level, I wonder if imperfectly modeled dynamic flexing or vibrations under flight loads could have fractured something or caused a seal or joint to leak. You can test for an hour of firing time on a test stand with 2 dozen engine starts and not detect that sort of problem. That could explain failure on or just after liftoff but not on the pad or test stand.

My dad was quality control manager of the Rocket Division of Bell Aerospace during the mid to late 60's. His inspectors signed off on the Lunar Module ascent engines which Bell built. One of the things he was most proud of was persuading upper management to spend some 2 million mid-1960's dollars in a test stand/facility in which they could hot fire the engined while undergoing flight-like (they hoped) vibration and shaking in 3-axes or more. At least one engine that had passed all inspection and static testing requirements FAILED on the test stand. All engines flown on Apollo missions worked, other than the never-fired Apollo 13 ascent engine.

lmike · « **Reply #170 on:** 03/26/2006 06:22 am »

Besides the particular point, but is it not true that ablative nozzles are more prone to unequal nozzle wear and are more susceptible to produce asymmetric thrust, and lesser static test capabilities (can't burn them for as long, prior to launch)?

lmike · « **Reply #171 on:** 03/26/2006 06:43 am »

It seems, upon searching, that they've only run the Merlin (with the first stage tankage?) at full throttle for only 3 seconds in tests (to conserve the ablative?) ... The 'sympathetic' oscillations are an old rocket engine gremlin...

lmike · « **Reply #172 on:** 03/26/2006 07:05 am »

Good call to look at the injector as well. The pintle valve, AFAIK, is also more prone to produce anomalies in the flow and thrust due to random deposits at the edge.

Damon Hill · « **Reply #173 on:** 03/26/2006 07:06 am »

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lmike - 26/3/2006 12:22 AM

Besides the particular point, but is it not true that ablative nozzles are more prone to unequal nozzle wear and are more susceptible to produce asymmetric thrust, and lesser static test capabilities (can't burn them for as long, prior to launch)?

Yes they can; it's important that whatever roll control there is have enough authority to overcome
torque that could be generated by uneven wear of the throat/expansion nozzle.

Since the engine is supposed to be reusable, I have to assume that the ablative liner must be
replaceable. The RS-68 is good for more than twice the firing time of a normal ascent, but it
does have a finite rated life.

Tap-Sa · « **Reply #174 on:** 03/26/2006 08:39 am »

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Nick L. - 26/3/2006 7:02 AM

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Damon Hill - 25/3/2006 10:55 PM

How is axis roll controlled; is the turbopump exhaust duct steerable?

I don't think the turbopump exhaust is steerable, I don't see any actuators on the exhaust.

It is. Check SpaceX site engine section. The exhaust is just a light tube so the actuator does not need to be that big, possibly just an electric servo turning it.

braddock · « **Reply #175 on:** 03/26/2006 09:43 am »

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lmike - 26/3/2006 1:43 AM
It seems, upon searching, that they've only run the Merlin (with the first stage tankage?) at full throttle for only 3 seconds in tests (to conserve the ablative?) ... The 'sympathetic' oscillations are an old rocket engine gremlin...

An interesting point, because Gwynne Shotwell on the press call mentioned that they were going to move to test stand firing with the entire first stage in the future. But because they were still in simultaneous structural development while working on the Merlin, the Merlin test program wasn't performed with an attached first stage tank.

They certainly have test run Merlin engines for more than three seconds. I don't know about THAT particular Merlin, and as you say, not with the first stage tank AFAIK.

braddock · « **Reply #176 on:** 03/26/2006 10:07 am »

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lmike - 26/3/2006 2:05 AM
Good call to look at the injector as well. The pintle valve, AFAIK, is also more prone to produce anomalies in the flow and thrust due to random deposits at the edge.

Here is Musk's technical update in which he talked about the pintle performance.

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The only fly in our ointment is that the pintle injector is not delivering quite the hoped for level of mixing efficiency at higher pressures (780 psi) and flow. We seem to have hit a ceiling at about 94% combustion efficiency, which is 2% below the target spec.

To make up for it, we have boosted nominal thrust from 72,000 lbs to 77,000 lbs (sea level). The higher thrust to weight on liftoff makes up for the drop in Isp, so payload performance to orbit is about the same. Nonetheless, it is a bit disappointing. Final vacuum Isp, including gas generator losses, will be around 304s rather than 310s. There is still some hope of tuning injector geometry and squeezing out more performance during the qualification program, otherwise improvements will have to wait until after first launch.

For the long term, we are evaluating other injector types, in particular a modified co-axial unique to SpaceX. Design is underway and we should have hotfire comparative test data this summer.

It is surprising that they are unhappy with the pintle, since one of their first employees and VP Propulsion is Tom Mueller from TRW.
Mueller ran the TRW rocket development department, which was doing a lot of pintle work throughout the 90's.
http://spaceflightnow.com/news/n0009/26trwpintle/

In fact, Musk went to court for the pintle, because Northrop (new owner of TRW) sued them claiming that Mueller had broken his NDA.

Note that the pintle lawsuit was on-going around the time Musk made his negative pintle comments, so maybe it was just a slight at Northrop. A quote from Musk at the time: "We will get to our objectives, in spite of the bloody pintle." ( http://www.astroblog.net/astroblog/archives/2005/02/spacex_fights_n.php )

-braddock

Tap-Sa · « **Reply #177 on:** 03/26/2006 10:14 am »

There's been testfiring with entire rocket on the pad at Vandenberg. Not a full length though, AFAIK those have been just with the engine on test stand. Notice how upper engine section stays clean, compared to being engulfed in a fireball at T+1 as already mentioned. Could the ensuing fire above the nozzle just be unburned fuel (from fuel rich turbopump exhaust etc) deposited by the flashback, without an actual leak? It seems the puny Omelek milkstool really needs some work.

braddock · « **Reply #178 on:** 03/26/2006 10:46 am »

Can anyone tell me about the expected nature of the formal US Government anomaly investigation that SpaceX announced last night? Is it standard practice for a formal government investigation of any government-customer launch failure?

InfraNut · « **Reply #179 on:** 03/26/2006 12:27 pm »

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hyper_snyper - 26/3/2006 1:38 AM

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DaveS - 25/3/2006 6:47 PMAnd there's some updates in the blog: http://kwajrockets.blogspot.com/Seems like the Falcon impacted a reef 250 ft(75 m) from the launch pad! And their machine shop got an unexpected visitor when the FalconSat-2 payload survived the failure mostly intact.

I wonder if he meant the second stage or some portion of it with FalconSat-2 still inside. Because I fail to see how FalconSat got out of the fairing and landed independently of the rocket.

Fairings are usually one of the weakest part of a rocket (radically mass-optimized). There are also two halves. It is probably unlikely that the fairing stay connected in any destructive event such as this.

The connection of the satellite to the payload adapter cone should be less weak, but it is designed to separate at deploy, so it is not suprising if it came loose.