SpaceX Falcon 9/Dragon CRS SpX-1 MISSION GENERAL DISCUSSION

[MP99]

They don't intentionally load mismatched lox & kero. There is a call during both first & second stage f9 ascent, something like "propellant usage active", signalling they are adjusting MR to ensure lox & kero are exhausted at the same time. You see the same on ULA telemetry as RL10 MR adjusts.

ISTM it only needs to get this fractionally out to end up with the tiny imbalance they suffered. Maybe related to this still being a young LV.

cheers, Martin

Yes, in my original post on this I was thinking only about propellant margin and not about LOX/kero usage ratio. I doubt it is possible to control mixture ratio accurately enough so that one propellant component is not left "wasted." (Anyone who knows otherwise feel free to correct this assumption.)

I suspect it is partly a matter of degree - something where the accuracy improves as the experience of multiple launches increases. However, I believe they'd always want to avoid an oxygen-rich shutdown, so there may be a deliberate policy to always have the lox run out slightly before the kero "just in case".



I also wonder regarding the wording of the quote below.

I take it either to mean that there is some uncertainty in the amount of prop that would be consumed by the burn, or about exactly how much prop was left in the stage - probably some combination of the two. Thus why it was not stated as "5% short of the prop we needed", but as a percentage likelihood of completing the burn:-

Some good reading:  http://www.newscientist.com/blogs/shortsharpscience/2012/10/satellite-ride-sharers-spacex.html

key quote:

"While there was sufficient fuel on board to [lift the satellite], the liquid oxygen on board was only enough to achieve a roughly 95 per cent likelihood of completing the second burn, so Falcon 9 did not attempt a restart," says SpaceX spokesperson Katherine Nelson.

cheers, Martin

[SpacexULA]

Hoping theyll neer have another engine out is not an option. There will be engine-outs in the future, and adding margin is going to be needed. Falcon 9 v1.1 should be capable of enough margin.

Carrying enough extra fuel to compensate for engine out as early as MAXQ to complete not only the primary but secondary payloads on every mission would seem like a ridiculous exercise.

My assumption is they will never have enough margin to be able to recover 100% from a engine failure that early without a sacrifice.  IF that had been a Falcon designed for reuse of the 1st and 2nd stage they would have had margin enough to make the choice.

Lose the Secondary Payloads, or lose the 1st or 2nd stage.

Of course, reusable stages are still years out, so until then I don't see any realistic situation where they would have he margin to lose an engine that early and not lose at least the secondary payloads (or force the payloads to reduce their on on orbit operation lifetime by correcting their obit themselves)... But it's still impressive they had enough margin to save the primary payload IMHO.

 

[peter-b]

I also wonder regarding the wording of the quote below.

I take it either to mean that there is some uncertainty in the amount of prop that would be consumed by the burn, or about exactly how much prop was left in the stage - probably some combination of the two. Thus why it was not stated as "5% short of the prop we needed", but as a percentage likelihood of completing the burn:-

That was also my interpretation.

[Prober]

Wrong. There is no need to add more LOX, just not burn the upperstage longer than planned due to the problemd with the first stage. 

think he worded the question wrong Jim.   Should SpaceX add more margin in the 2nd stage?

No, my point still stands, because it was a secondary payload.  If you want more margin, then the secondary payload needs to be smaller.

think we've gone full circle and have come back to this thread with discussion. 

http://forum.nasaspaceflight.com/index.php?topic=12863.270   

Dan the man was right.

[kevin-rf]

Of course, reusable stages are still years out, so until then I don't see any realistic situation where they would have he margin to lose an engine that early and not lose at least the secondary payloads (or force the payloads to reduce their on on orbit operation lifetime by correcting their obit themselves)... But it's still impressive they had enough margin to save the primary payload IMHO.

Reusable does not mean that you will not still lose the primary and secondaries in the event of a launch anomaly.

A Grasshopper like boost back system does not have the thrust and propellant to boost back with the upper stage and payload still attached. If it does boost back, it will leave a very deep crater.  Only a shuttle like system might be able to pull that off. And that is a very big maybe...

[spacedem]

Of course, reusable stages are still years out, so until then I don't see any realistic situation where they would have he margin to lose an engine that early and not lose at least the secondary payloads (or force the payloads to reduce their on on orbit operation lifetime by correcting their obit themselves)... But it's still impressive they had enough margin to save the primary payload IMHO.

Reusable does not mean that you will not still lose the primary and secondaries in the event of a launch anomaly.

A Grasshopper like boost back system does not have the thrust and propellant to boost back with the upper stage and payload still attached. If it does boost back, it will leave a very deep crater.  Only a shuttle like system might be able to pull that off. And that is a very big maybe...

He meant that they could make the choice to sacrifice the reusable stage by using the propellant that would normally be used to land the stage as extra propellant for the boost instead.
 

[nlec]

If SpaceX were to perform a full-duration static test fire  on the pad before CRS SpX-2 (instead of the 3 second test fire) to help remove doubt about engine reliability, do those same engines still have enough rated life left for the actual mission?

Does a test fire of that length actually reduce their reliability for a second full-duration burn?

Thanks.

[douglas100]

Yes, in my original post on this I was thinking only about propellant margin and not about LOX/kero usage ratio. I doubt it is possible to control mixture ratio accurately enough so that one propellant component is not left "wasted." (Anyone who knows otherwise feel free to correct this assumption.)

I suspect it is partly a matter of degree - something where the accuracy improves as the experience of multiple launches increases. However, I believe they'd always want to avoid an oxygen-rich shutdown, so there may be a deliberate policy to always have the lox run out slightly before the kero "just in case".

cheers, Martin

Good pont.

[baldusi]

If SpaceX were to perform a full-duration static test fire  on the pad before CRS SpX-2 (instead of the 3 second test fire) to help remove doubt about engine reliability, do those same engines still have enough rated life left for the actual mission?

Does a test fire of that length actually reduce their reliability for a second full-duration burn?

Thanks.

Starts are particularly hard on the engines. But normal use also is. If you concentrate on the steady state (since the start is done while clamped and you can abort). Then you could see the engine as a stochastic variable with an (monotonically increasing) chance of failure. The longer you run it before the mission, the longer you chance it that it might fail.
The fact that the anomaly happened at Max-Q has some people wondering if it wasn't related. In which case, a full duration burn wouldn't have meant squat. Until they identify the root cause, there's little to do but very wild speculations.

[Robotbeat]

Of course, reusable stages are still years out, so until then I don't see any realistic situation where they would have he margin to lose an engine that early and not lose at least the secondary payloads (or force the payloads to reduce their on on orbit operation lifetime by correcting their obit themselves)... But it's still impressive they had enough margin to save the primary payload IMHO.

Reusable does not mean that you will not still lose the primary and secondaries in the event of a launch anomaly.

A Grasshopper like boost back system does not have the thrust and propellant to boost back with the upper stage and payload still attached. If it does boost back, it will leave a very deep crater.  Only a shuttle like system might be able to pull that off. And that is a very big maybe...

If the Payload is something like Dragon, relatively intact abort is still possible if you can't make orbit. Do a controlled staging, then separate the Dragon from the upper. The first and second stages can dump most of their propellant (probably through the engines, i.e. just burn it off), hopefully can find  someplace to land (probably needs to be decided ahead of time), and the Dragon can land or splashdown somewhere. Intact abort. Hard, but not impossible even for a VTVL two-stage vehicle.

If the payload is a satellite and you still wanted intact abort, you'd need even more design compromises. You'd need to use a big, recoverable payload fairing... perhaps a fat Dragon capsule that can open up (READ: very heavy). That's essentially what the orbiter was... a big, recoverable payload fairing with some maneuvering capability for precise orbital insertion and docking/rendezvous (well, and the main engines and a crew capsule attached... Buran didn't have the main engines attached and was only optionally manned, so is even closer to this recoverable payload fairing concept).

But it doesn't HAVE to land horizontally, and perhaps more payloads would rather you didn't land horizontally, since they usually can't take the belly-flop of reentry and landing for a Shuttle-style horizontal system, while a vertical landing would have loads very similar to launch, which the payload has to survive anyway.

If Shuttle aborted to a landing site with a payload still inside before it could be deployed, usually that meant the payload would've been significantly damaged or destroyed... luckily that never happened.

[Jason1701]

If SpaceX were to perform a full-duration static test fire  on the pad before CRS SpX-2 (instead of the 3 second test fire) to help remove doubt about engine reliability, do those same engines still have enough rated life left for the actual mission?

Does a test fire of that length actually reduce their reliability for a second full-duration burn?

Thanks.

The stage would have already been full-duration static fired in Texas. Also, F9 pad is likely not built to support a static fire for more than a few seconds.

[ugordan]

The stage would have already been full-duration static fired in Texas.

Not full duration, they do shorter tests. I think the record holder up until now might have been F9-03 stage due to a couple of aborted tests and their redos, amounting up to perhaps 1/2 of nominal stage burn time on the engines.

[JohnFornaro]

Sheesh.  How many posts can you get in a few days?

IMO, pause the video at exactly 30 seconds and take a look at what you see full screen. It appears to me the failure of the fuel dome resulted in a small explosion as opposed to just depressurization. It looks, however, like the engine shutdown command went through such that by the time the rupture/explosion was occurring, the engine was already terminating its fuel/oxidizer supply and shutting down, which may be why it was as small as it was. So really it was ultra rapid depressurization or essentially a very small brief explosion that was contained.

I just checked my armchair to verify that it was at the proper level.

I'm going to say that this is the principle of what happened:  They received an anomalous reading from the engine and shut it down as quickly as they could.  The "detonation", or whatever it was, had already started, but had only gotten so far.  The shut down command got there in time to keep fratricidal damage to a minimum.

Not nearly as much as Antares and some of the other NASA folks on this forum. I always look forward to their posts, not some guy with a friggin' log on his shoulder.

what log?

He woulda said "chip", but it's the intertubes, so he gets to exaggerate.   And what's all that chatter about sending up "trinkets"?  I thought they were only allowed to send up "wampum".

./..the Jim Update thread...

Ootay unnyfay.

[mr. mark]

What I find interesting is that my assumptions about the launch vehicle were completely wrong. I though that Dragon would end up being the long pole in all of this. Now it seems that Dragon is performing just fine and the Falcon 9 launch vehicle is what is taking time to straighten out.

[meekGee]

Hoping theyll neer have another engine out is not an option. There will be engine-outs in the future, and adding margin is going to be needed. Falcon 9 v1.1 should be capable of enough margin.

Carrying enough extra fuel to compensate for engine out as early as MAXQ to complete not only the primary but secondary payloads on every mission would seem like a ridiculous exercise.

My assumption is they will never have enough margin to be able to recover 100% from a engine failure that early without a sacrifice.  IF that had been a Falcon designed for reuse of the 1st and 2nd stage they would have had margin enough to make the choice.

Lose the Secondary Payloads, or lose the 1st or 2nd stage.

Of course, reusable stages are still years out, so until then I don't see any realistic situation where they would have he margin to lose an engine that early and not lose at least the secondary payloads (or force the payloads to reduce their on on orbit operation lifetime by correcting their obit themselves)... But it's still impressive they had enough margin to save the primary payload IMHO.

 

That's true, and is a game of optimization, up until reusability comes in.

Once F9R flies, there's a fuel reserve used for a) return to base, and b) land.

So if for whatever reason an engine failed right on launch, and the vehicle ended up ascending slower and therefore burning more fuel, the payload is safe no matter what, and now we're talking about the safe return of the vehicle - maybe land at a contingency site downrange, maybe lose the rocket.

(If you have a fleet of rockets, losing one is just a matter of capital cost, which can be insured.  This is different than a satellite which can easily be a one-of-a-kind for the customer)

[Chris Bergin]

Update / SpaceX CRS-1 Mission: October 12

 

NASA and SpaceX announce that they have jointly formed a CRS-1 Post-Flight Investigation Board. This board will methodically analyze all data in an effort to understand what occurred to engine 1 during liftoff of the CRS-1 mission on Sunday, October 7. While Falcon 9 was designed for engine out capability and the Dragon spacecraft has successfully arrived at the space station, SpaceX is committed to a comprehensive examination and analysis of all launch data, with the goal of understanding what happened and how to correct it prior to future flights. Additional information will be provided as it is available.

 

[kevin-rf]

January looks a lot less rosy now

Glad to see they are taking the anomaly seriously!

[Prober]

If SpaceX were to perform a full-duration static test fire  on the pad before CRS SpX-2 (instead of the 3 second test fire) to help remove doubt about engine reliability, do those same engines still have enough rated life left for the actual mission?

Does a test fire of that length actually reduce their reliability for a second full-duration burn?

Thanks.

that 3 second test fire "could" have caused the problem of this one engine....we just don't know yet.

[Prober]

Glad to see they are taking the anomaly seriously!

like they have a choice?

[Robotbeat]

Glad to see they are taking the anomaly seriously!

like they have a choice?

The Russians, it was said, would just sweep away the debris and launch the next 'un.