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

[baldusi]

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.

From what I read they did very thorough analysis. At first, of course, they lacked the experience and the support infrastructure to get to the root cause. But reading Rockets and People I got a new found respect for their system.
You might say that when they didn't find a cause they tend to say it's "a manufacturing defect" or  "somebody left a rag". But the second Taurus failure had also supposedly found the fairing's root issue. If you consider the number of stages they launch per year, their average is not bad at all. They just design relatively unreliable hardware because it's cheaper or because they have some serious transport and launch site limitations.

[woods170]

January looks a lot less rosy now

That is speculation on your side.

[mikegi]

Couple of things I was wondering about:

1. What effect would the engine problem have had if it was much earlier in the flight? Would Dragon have made it to orbit? Would the damage pattern have been different (e.g. would it have been more likely to cause problems with the other engines because of the lower altitude)?

2. If this was a manned Dragon, would the mission have been aborted when the failure occured? I'm not sure of the Dragon abort system so I don't know if it would have been available at that time (i.e. jettisoned or rendered inactive).

Thanks

[peter-b]

2. If this was a manned Dragon, would the mission have been aborted when the failure occured? I'm not sure of the Dragon abort system so I don't know if it would have been available at that time (i.e. jettisoned or rendered inactive).

I imagine that an abort condition would have been triggered if and only if the flight controller decided that there was insufficient margin to reach the target orbit and that an abort-to-orbit was also impossible to achieve. In the SpX-1 case, I don't think that the escape system would have been activated.

[john smith 19]

Orbcomm confirmed re-entry of satellite...

http://www.orbcomm.com/Collateral/Documents/English-US/OG2%20Prototype.pdf

press release however sounds very strange and controversial... basically

Not really. Realizing their satellite had a short orbital life time they have truncated the commissioning phase.

They are also trying to put the most positive view on the events and put out the message that (basically) it's NASA's fault for having this gate.

Think of it like buying a satellite decoder. Got it home? Check. Unpacked box? Check. Connected it up? Check Switched on and running? Check.

But what this does *not* do is allow them to test for *endurance* of on orbit hardware (EG thermal cycling in a vacuum over a *long* period over what about 90mins ) and signal strength (other posters mentioned the output from this altitude will be *loud* to ground receivers).

Weather they have a claim depends on the exact rules in the policy. It did not make the requested orbit and the orbit it did make has a *very* limited life expectancy. They sound like pretty good grounds for a full claim to me.

Intriguingly the tone of it *suggests* they are *not* going to launch a 2nd test mission but going ahead with launching the constellation as planned on F9's and pocket the cash (paragraph 3)

[kevin-rf]

Couple of things I was wondering about:

1. What effect would the engine problem have had if it was much earlier in the flight? Would Dragon have made it to orbit? Would the damage pattern have been different (e.g. would it have been more likely to cause problems with the other engines because of the lower altitude)?

Considering the Falcon has shielding for a turbine RUD around each Merlin I doubt the actual damage would have been much different. Remember it was a sudden pressure drop in the fuel dome, the turbines shut down safely and the cutoff valves held. MaxQ was about the worse point for tearing stuff off after that sudden pressure drop.

[bob the martian]

Glad to see they are taking the anomaly seriously!

like they have a choice?

I don't understand why people think they wouldn't take it seriously.  Their business success hinges on reliability, and while they've demonstrated that their engine-out capability is more then just hype, life's just plain easier for everyone when everything works as expected.  Of course they're going to take this seriously, analyze the data, attempt to find the root cause and correct it if possible.  I would hope that by now SpaceX has shown that they're in this business for real, that they intend to be a player in commercial space flight. 

[Joffan]

Think of it like buying a satellite decoder. Got it home? Check. Unpacked box? Check. Connected it up? Check Switched on and running? Check.

But what this does *not* do is allow them to test for *endurance* of on orbit hardware (EG thermal cycling in a vacuum over a *long* period over what about 90mins ) and signal strength (other posters mentioned the output from this altitude will be *loud* to ground receivers).

Weather they have a claim depends on the exact rules in the policy. It did not make the requested orbit and the orbit it did make has a *very* limited life expectancy. They sound like pretty good grounds for a full claim to me.

Intriguingly the tone of it *suggests* they are *not* going to launch a 2nd test mission but going ahead with launching the constellation as planned on F9's and pocket the cash (paragraph 3)

That was the main test item on my reading of the Orbcomm test program too. Endurance time in orbit. However,  two points:
1.  I'd think the close-in orbit would be somewhat worse for thermal cycling, with a higher proportion of night-time (still not 50% of course).
2. Endurance is never going to be something you finishing testing, in one sense. Of course you want some minimum endurance but you only ever accumulate evidence, never a strong yes/no like some tests.

And like you, I read this as saying they'd seen enough to calm their strongest concerns prior to operational launch, and they just intend to go for full deployment. The insurance companies are likely to take this as meaning that Orbcomm got some significant utility out of this missions - and I'd guess they did, even if not the whole of the actions that they were intending. The negotiation on the value of that unfulfilled expectation will no doubt take a little time.

[john smith 19]

I'm sure he's saying excess fuel over the O2 to burn it.

The prop left for the restart is a small proportion of the total upper stage prop at launch. I suspect it needs only a tiny imbalance of consumption of O2 over kero during ascent to just leave a slight imbalance of kero over O2 for the restart. Thus, enough kero but not enough O2.

cheers, Martin

Note while it sounds like a great idea to *precisely* load just enough propellant to get *maximum* payload to the planned orbit the joker in the pack is statistical uncertainty. So *all* launchers are overloaded with propellant to ensure they reach orbit.

Naturally the better the tanking system, the lower the needed margin.

But to minimize the excess mass the aim is to ensure that while *both* propellants are loaded in excess the *lighter* one runs out *last*.

[MP99]

Makes more sense to adjust the mixture ratio so that both reach their minimum levels (residuals) at the same moment.

cheers, Martin

[baldusi]

Makes more sense to adjust the mixture ratio so that both reach their minimum levels (residuals) at the same moment.

No all engines can adjust the mixture ratio. But even if you could, there's some stochastic component to the amount of fuel left. And you want some reserves in case you have some slight under performance. What's more, an oxidizer rich shutdown might have catastrophic consequences. So, just in case, you bias towards an excess of fuel. Not to mention that in the particular case of LOX/RP-1 you have boil off issue only with the oxidizer. If you had to burn longer, particularly after an engine out, the boil off losses would have accumulated. So the bias would have been even bigger.
And in any case, for this particular mission, it was a "problem" of extremely tight requirements on a payload that wasn't worth too much risk reduction measures.

[john smith 19]

No all engines can adjust the mixture ratio. But even if you could, there's some stochastic component to the amount of fuel left. And you want some reserves in case you have some slight under performance. What's more, an oxidizer rich shutdown might have catastrophic consequences. So, just in case, you bias towards an excess of fuel. Not to mention that in the particular case of LOX/RP-1 you have boil off issue only with the oxidizer. If you had to burn longer, particularly after an engine out, the boil off losses would have accumulated. So the bias would have been even bigger.
And in any case, for this particular mission, it was a "problem" of extremely tight requirements on a payload that wasn't worth too much risk reduction measures.

Nice summary. Note also the issue was that at the propellant loading on the 2nd stage the simulations estimated "only" a 95% chance of reaching the correct new orbit versus a required confidence level of 99%.

I'll note that due to propellants density changing due to temperature and atmospheric pressure it's normal to measure their loading by their mass. Modern weighing systems can weigh a structure the size of the Shuttle stack (c2million kg) to the nearest Kg.

[Robotbeat]

We don't know that. Insufficient information in the press release.

Well, I assume January is goner until proven otherwise. I do not believe they can do it (investigate, correct and test) in less than three months. I assume there was no external damage to engine (worst case).

They may indeed be able to. I wouldn't count it out, yet. Remember how quickly they trimmed the nozzle?

Then again, if I were a betting man, I wouldn't bet anything on it happening in January, either. What is the current NET launch date for CRS-2?

[Comga]

Our expert Jim has stated that tanks are loaded full.  With that, most of the comments on loading are irrelevant. 

With pressure and temperature fixed by design and environmental conditions, the fuel and oxidizer masses are known at launch.  After that I believe they have to estimate based on how long and hard the engines have burned.  The uncertainties result in the probabalisic limits that were the criteria for the second stage relight.

Maybe the controller can adjust the mixture ratio, but that's about all that can be adjusted that I can see.  However, until someone knowlegeable says that rockets do this, I will remain highly skeptical.

[Comga]

(snip) What is the current NET launch date for CRS-2?

As said before, CRS-2 isn't even on anik's list.  Until it is, I don't consider it really scheduled, just planned.   It was planned for December 16th (IIRC) on some less reliable ISS planning schedule.

[LouScheffer]

Our expert Jim has stated that tanks are loaded full.  With that, most of the comments on loading are irrelevant. 

Maybe the controller can adjust the mixture ratio, but that's about all that can be adjusted that I can see.  However, until someone knowlegeable says that rockets do this, I will remain highly skeptical.

See for example, "Modern Engineering for Design of Liquid-Propellant Rocket Engines", page 221, for examples in real engines and a long list of reasons this might be desirable.

[LouScheffer]

Our expert Jim has stated that tanks are loaded full.  With that, most of the comments on loading are irrelevant. 

Maybe the controller can adjust the mixture ratio, but that's about all that can be adjusted that I can see.  However, until someone knowlegeable says that rockets do this, I will remain highly skeptical.

Here's someone fairly knowledgable (Werner von Braun) explaining how and why they do this, in "Popular Science" in 1964:

http://books.google.com/books?id=WCYDAAAAMBAJ&pg=RA1-PA166&lpg=RA1-PA166&dq=rl-10+rocket+engine+mixture+control&source=bl&ots=uOUfQ-ZmLr&sig=BofEm8AfCErEkxe6N8tKlwRBFBg&hl=en&sa=X&ei=wZR4UJ6-IO-80AHUk4DgAQ&ved=0CDoQ6AEwAg#v=onepage&q=rl-10%20rocket%20engine%20mixture%20control&f=false

If the link does not work, you can find this by typing ' "How is mixture ratio controlled" Braun ' into google - at least this worked for me.

[Norm38]

With regard to the announced investigation board and the next mission, there are three main possibilities:

1) A root cause is quickly determined, corrective action is minimal and the next launch is scheduled with minimal delay.

2)  A root cause is quickly determined, corrective action is intensive and the next launch is delayed until changes can be implemented.

3)  Root cause is indeterminate, with conflicting theories and no clear consensus.  Some changes are made, but it is not clear if the root cause has been addressed.


In the event of #3, IMHO, roll the dice and launch the last unmanned cargo flight with Merlin 1Cs and take data.  If that's the only way to learn and move forward.  They've got mass production set up, and engineering time for testing isn't cheap.  They could easily blow through more than the cost of an already built rocket with an obsolete engine if this drags out for a year.

In addition, and I'm sure Jim will correct me if I'm wrong, but if engine out capability is going to factor into man rating and crew survivability, does anyone really think NASA would allow that as a factor without seeing it in action more than once?

Might as well launch again, blow an engine, make orbit again and show everyone it wasn't a fluke.

[newspacer]

Makes more sense to adjust the mixture ratio so that both reach their minimum levels (residuals) at the same moment.

No all engines can adjust the mixture ratio. But even if you could, there's some stochastic component to the amount of fuel left. And you want some reserves in case you have some slight under performance. What's more, an oxidizer rich shutdown might have catastrophic consequences. So, just in case, you bias towards an excess of fuel. Not to mention that in the particular case of LOX/RP-1 you have boil off issue only with the oxidizer. If you had to burn longer, particularly after an engine out, the boil off losses would have accumulated. So the bias would have been even bigger.
And in any case, for this particular mission, it was a "problem" of extremely tight requirements on a payload that wasn't worth too much risk reduction measures.

F9 has a propellant utilization system which uses a fuel trim valve between the fuel pump and injector on each engine to do exactly what MP99 is suggesting.

[Nomadd]

In addition, and I'm sure Jim will correct me if I'm wrong, but if engine out capability is going to factor into man rating and crew survivability, does anyone really think NASA would allow that as a factor without seeing it in action more than once?

Might as well launch again, blow an engine, make orbit again and show everyone it wasn't a fluke.

Engine out capability is meant to be an additional safety factor, not an excuse to lower standards. I'm not sure if NASA would approve of the system because it had that ability if they wouldn't approve without it.