SpaceX Falcon 9 Statement on First Stage Engine Anomaly | Hacker News Reader

SpaceX Falcon 9 Statement on First Stage Engine Anomaly

spaceref.com

119 pointsceejayoz37 comments

Note additionally it's being reported that the secondary payload on this flight, an Orbcomm sat, did not get deployed into the correct orbit because the Falcon upper stage insertion burn failed. No info on whether or not this was a related failure. Info at the moment just seems to be social networks, can't find anything more solid: https://www.facebook.com/jsrpage/posts/10151048911726680

Bad Astronomy [1] has a comment saying the Orbcomm satellite is a test unit (not the production unit yet) and that a second-choice orbit is possibly where it will be released.

[1] http://blogs.discovermagazine.com/badastronomy/2012/10/08/sp...

I read it as that they have already deployed rather than will be. But yes, the comment seems to suggest that the idea of trying to put it into the nominal orbit was abandoned, the speculating being that the 2nd stage had to burn for longer to get the dragon/ISS primary payload as it should be, and so not leaving enough fuel left over for the secondary payload nominal insertion. That sounds plausible, but equally SpaceX haven't said anything so it's all just armchair speculation, which is fun anyway.

Spaceflightnow.com has some more details:

http://spaceflightnow.com/falcon9/004/121008orbcomm/

Just for the record, since this topic is getting old as these things go, the upper stage insertion burn didn't happen because the longer burns of the first two stages wouldn't allow it without it getting to close to the Space Station, which has very wide margins for safety (i.e. as far as they know the burn could have happened, they didn't try). Sounds like a bet on a cheaper flight that didn't pay off for Orbcomm, although it remains to be seen if they can get any use out of the satellite.

" I believe F9 is the only rocket flying today that, like a modern airliner, is capable of completing a flight successfully even after losing an engine."

Brilliant! By equating the rocket with an airliner (the statistically safest way to travel), this turns what could be a mark against into a huge mark for.

While this is indeed an awesome feature to have, it doesn't by itself mean much. The total reliability of course also depends on the probability that one engine will fail, a rocket that needs all its engines may still be more reliable than one that is capable of of flying with two failed engines, but regularly has to do so.

What makes the airliner seem safe is that it can fly with a failed engine and it very rarely loses an engine.

I guess we will have to wait for some more flights till we have decent statistics on the reliability of the Falcon 9. Of course, I'm hoping that it will turn out to be an awesome rocket!

For whatever it may be worth, it seems right now the engine failure rate for Falcon 9 is 1 in 27.

Is there a similar rate known for regular jet engines?

No idea. I am sure it is astronomically small though.

A lot of Western aviation qualifying authorities specify a maximum allowable mean time between failure (MTBF) of 1 per 100000 flight hours. I imagine most rocket engine designs would be more like one per hour! That said, they only have to operate for about ten minutes though before they are disposed of, in the case of expendable launch vehicles.

In Falcon 9's case, and totally from memory and probably incorrect and very approximate, we've had 4 launches, each has had 9 Merlin C engines on the first stage, the first stage burn time is 170s or about 3 minutes. There have been two failures - a non destructive engine shutdown on the previous ISS mission on the pad at T-very_little, and the rather more messy rapid disassembly failure of something near the engine or the engine itself on the most recent launch.

So, for this first stage engine the MTBF (remember this is all a bit silly and inaccurate and just for ballpark comparisons with the airline industry) the MTBF has been:

9(engines/launch)4(launches)0.05(3 min burns in hours)*0.5(2 failures) = 0.9, i.e. a MTBF of 55 minutes for Merlin 1C lower stage, vs most regulators requiring mtbf > 100000 hours on commercial jet airliner engines.

So there's a bit of a way to go yet!

Ah yes, good stuff. I forgot about the aborted launch, and the initial Falcon 9 launch without Dragon. My 1/27 figure, in addition to being overly simplistic, is wrong.

I agree that there is plenty of room for improvement, but you can't launch a rocket with commercial jet engines.

I don't know if it makes sense to normalize for thrust or not, but it seems like thrust should be included somehow.

They're not saying, "commercial jet engines are more reliable; therefore we should use them". The issue is that the Merlin 1C engine simply hasn't had enough flights to build up its denominator.

It doesn't make sense to normalize for thrust here. This is just failure rate. There's nothing wrong with having a comparatively high failure rate when the sample size is several orders of magnitude smaller: the statistical significance is just weaker; we acknowledge that and move on.

Here's a 1993 paper giving MTBF failures for the space shuttle's main engine. With some improvements that the author of the paper suggests, it looks like MTBF is about one per 254 flights at 100% power and one in 139 flights at 104% power . (It drops to one in 20 flights at 109% power! It's surprised the failure rate has such a strong dependency on power output --- the relationship suggests that failures have something to do with thermal stress.)

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/1993001...

It's interesting to compare that MTBF with the fact that there are about ten million airliner flights per year in the US. If we arbitrarily assume that the average airliner flight is two hours, that's a substantial number of failed engines per year, so obviously the redundancy on these craft really does work.

Incidentally, I went searching for airliner engine MTBF statistics and your comment was already near the top of Google's results.

Edit: erroneously said five million flights per year because I was looking at 2012 statistics for only the first six months. of the year. Oops.

Doesn't seem to be the whole story, since the video clearly shows a significant amount of debris. A simple shutdown wouldn't produce debris, although the loss of internal pressure on the engine bell could cause it to collapse and possibly disintegrate.

I look forward to seeing a more complete analysis.

I, too, am looking forward to a full analysis, but I think it helps to recall that this occurred at or near maxQ (maximum dynamic pressure). At these stresses, pretty much anything looks like an "explosion". For example, the Challenger didn't "explode", per se (there was not an ignition as the root cause of failure), but rather "broke up"...though it sure as hell looked like it exploded.

From what I understand, engine exhaust is too hot for any material to withstand without active cooling, which is done as a side-effect of feeding in the fuel. If you just turn it off, then, it's no longer actively cooled, and will rapidly melt from all the other engines around it still going full bore.

This is just a theory.

The engine exhaust is very highly directional, it doesn't just go everywhere. For example, the supporting structures around the engines are exposed to the same level of exhaust as a shut-down engine would be, and they are completely uncooled.

Here's the latest statement from SpaceX:

SpaceX CRS-1 Mission Update: October 8, 2012 http://www.spaceref.com/news/viewpr.html?&pid=38825

"Approximately one minute and 19 seconds into last night's launch, the Falcon 9 rocket detected an anomaly on one first stage engine. Initial data suggests that one of the rocket's nine Merlin engines, Engine 1, lost pressure suddenly and an engine shutdown command was issued immediately. We know the engine did not explode, because we continued to receive data from it. Our review indicates that the fairing that protects the engine from aerodynamic loads ruptured due to the engine pressure release, and that none of Falcon 9's other eight engines were impacted by this event."

No explosion according to them.

More info and a video from The Bad Astronomer (Phil Plait): http://blogs.discovermagazine.com/badastronomy/2012/10/08/sp...

"There was no effect on Dragon or the Space Station resupply mission." - Elon Musk

Just for those who didn't closely follow the events.

I think we'll see an expanded statement later today when they've had time to analyze the data more thoroughly.

I would hope that it would be later than later today, and that they would take an appropriate amount of time to analyze all the data...

There will be a full investigation however the video clearly shows more than just an engine shutdown. Something else happened and this needs some clarification. There's a lot riding on this mission both politically and financially.

Yes, and it is for that reason that I hope they take their time. SpaceX is very much a pioneer in this space, and how they handle each situation will set the benchmark, for better or worse, for those that come after.

I thought the way they handled the launch abort during the last mission was done very professionally. Likewise, I hope they handle this situation in a manner that underscores the complexity of putting things in space, but also instills confidence that they are up to the task. If they have to walk back any early mis-diagnoses, it could tarnish their image more than a delay in releasing the full details.

How many engines does it take to cause failure?

The Falcon 9 has two engine-out capability.

I believe Falcon 9 has 2 engine out capability.

probably not any 2 engines though, right? I'd guess if the two engines on one side fail it can't recover, since it could only proceed with 1/6th capacity through the middle engines. (They have 6, right?)

Any 2 engines.

Side engine loss is compensated by its opposite side engine reducing thrust (along with those in-between - in ratio).

This leads to a longer burn and slightly greater fuel waste - but it is stable and was designed just for this very occasion.

They have 9, thus Falcon 9.

I'm not familiar with the specifics of Falcon9 redundancy. But in theory, losing many engines can be completely recoverable, because all 9 engines share a single fuel tank.

Outside of atmosphere, a rocket's final speed and orbit depend on three factors: the mass of the payload, the mass of the fuel, and the inherent engine design efficiency. Notably, it does not depend on thrust. Burning one engine for 9 seconds results in a speed boost equal to burning 9 engines for 1 second.

Even if an engine fails and another one is set to reduced thrust, the fuel is still there, and can be burned by remaining engines.

Of course, this is a huge simplification, and loss of thrust while still in atmosphere or near the ground might be a problem.

I think thrust counts to a degree, as you'll lose velocity from gravity drag if the time to orbit is too high. The degenerate case would be if your thrust is less than the weight of your rocket (i.e. not moving).

everybody interested in why rocket engines have the amazing ability to turn thrust into fireworks when least expected should read this excellent book on rocket propellant history: http://library.sciencemadness.org/library/books/ignition.pdf. to spark your interest, foreword was written by isaac asimov.

This thread is pretty cold by now but I wanted to thank you for the link to Ignition — it's a really neat window into some of the chemistry and practice of 20th century rocketry. Reminded me of Max Gergel's "Excuse me sir, would you like to buy a kilo of isopropyl bromide?" http://library.sciencemadness.org/library/books/gergel_isopr... which, now that I look at the link, is hosted at the same server.

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