On: Satellite burns up following SpaceX rocket glitch

[martinkallstrom]

It is perfectly clear that this is a story of safety margines adhered to in an admirably strict fashion; not allowing short term thinking rule over long term; and certainly not allowing marketing rule over engineering. This is how you move mountains.

[codex → martinkallstrom]

It should; all of the material quotes in this article came from a SpaceX public relations agent and not from independent space analysts. Not exactly objective. The only quote from Orbicomm is practically a tautology.

[codex → codex]

In looking at this a bit further, it seems that the reliability of the Falcon 9 is not looking so good. It has only flown four times and suffered single engine shutdowns on two of them (the other: http://www.spacenews.com/civil/spacex-acknowledges-falcon-en...). See also: http://www.americaspace.org/?p=9044.

Simple probability then gives a failure rate of 3%. I have not attempted the Bayesian analysis.

[saraid216 → codex]

FWIW, they're going to be using a different engine soon.

[aeontech]

You are mixing your terms I think. (2/4)^3 is the chances of the next launch also having a single engine failure.

The chances of a single engine failing in a launch based on these four launches should be 2/36, two engines failed out of 36 fired total.

So, assuming that a single engine failure does not increase failure chance of nearby engines (which is not true probably), and assuming past performance is indicator of future performance, and discounting all the test fires that they have done with the rocket, the formula should look more like the following:

Chances of any given 3 engines failing is the inverse of the chances of at least two engines failing at the same time.

Chances of at least two engines failing equals no engines failing + 1 engine failing + 2 engines failing

Based on current engine failure rate, that's (17/18)^9 + (1/18)^8 + C(9,2) * (1/18)^2 * (17/18)^7

where C(9,2) = 9!/(2! 7!) = 36

So that looks more like 98.88% chance of two or fewer engines failing, the converse of which is about 0.02% chance of a triple or more failure.

(math is not my strong suit, please correct me if I'm wrong, but #math on IRC thought this looked correct).

[ordinary → aeontech]

> Based on current engine failure rate, that's (17/18)^9 + (1/18)^8 + C(9,2) * (1/18)^2 * (17/18)^7

I think the second part of that calculation is incorrect. I'm getting:

  P(0 engine fail) = (17/18)^9 ~= 0.5978
  P(1 engine fail) = (17/18)^8 * (1/18) * C(9,1) ~= 0.3165
  P(2 engine fail) = (17/18)^7 * (1/18)^2 * C(9,2) ~= 0.0745

Adding those together gives:

  P(<=2 engine fail) = (17/18)^9  +  (17/18)^8 / 2  +  (17/18)^7 / 9 ~= 0.9888

That's the same answer you came up with, so I guess you have the correct calculation written down somewhere. Moving to 3 or more engine fails then gives:

  P(>=3 engine fail) = 1 - P(<=2 engine fail) ~= 0.0112

[aeontech → ordinary]

you're absolutely right, i was doing the final subtraction in my head and not paying attention...

[dbaupp → aeontech]

Not commenting on the correctness or otherwise of the rest, but 98.88 + 0.02 != 100. (You probably want 1.12% chance of triple or more failure.)

[aeontech → dbaupp]

d'oh! thanks :)

[codex → aeontech]

I believe this is correct. I had too few digits of precision in my original calculation; rounding is bad!

[RockyMcNuts → martinkallstrom]

Perfectly clear that PR best practices were adhered to in an admirably strict fashion - show beautiful pictures of apparent success on live video, bury the part where the satellite burns up until after hours on a Friday!

[mbenjaminsmith → RockyMcNuts]

Apparently you know nothing about PR "best practices". No consultant worth their salt would have allowed SpaceX to handle the secondary mission failure they way they did. They made a series of classic and potentially disastrous mistakes. The best thing they could have done was address the issue head on with what information they had and then filled in further details as they were known.

To build credibility you have to admit failure. You can't just omit the bad news while focusing on the good news. You can't allow rumor and speculation to be your spokesperson. There's no way around the fact that an engine failure led to the failure of their secondary mission. Test platform or not, fully insured or not, an expensive piece of hardware became a shooting star. Someone didn't get what they paid for.

How it was handled was seriously amateurish. It made me cringe because I really want to see SpaceX (and Musk) succeed. Shit happens, but how you respond to that as an organization defines you for better or worse.

[danielweber → RockyMcNuts]

Everyone in the industry who was paying attention knew that the satellite was having problems on Tuesday. Anyone who wanted to know about it did.

The satellite burned up when it burned up. It was very probable that it was going to have a short life, but no one really knew how short until re-entry was imminent.

[Dylan16807 → martinkallstrom]

On the other hand it doesn't explain why they didn't look at another orbit that they did have enough fuel for. Was this a decision that had to be made immediately?

[sp332 → Dylan16807]

A group of communications satellites have to be deployed in a synchronized way, to continuously cover the area they target. Changing the orbit of this satellite would mean changing the orbits of the other 16 satellites as well. Also I'm pretty sure you have to license a particular orbit ahead of time instead of just picking whatever is convenient at the moment.

[Dylan16807 → sp332]

Were they putting this into the exact same orbit as the others? I thought it was mostly a test sat.

Who do you license orbits from?

[gus_massa → Dylan16807]

I googled a little, and apparently the radiocommunication satellites are regulated by ITU: http://www.itu.int/en/about/Pages/whatwedo.aspx .

[ktizo → Dylan16807]

Issac Newton got quite bored after becoming immortal and now has a little booth set up at the patent office. Don't take the piss out of his wig, otherwise you will get nowhere with him.

[InclinedPlane → Dylan16807]

I strongly suspect it was so that they could collect the maximum amount from insurance as quickly as possible. No other explanation makes as much sense.

[danielweber → Dylan16807]

They didn't fire at all because there was a risk that they might have hit the ISS. SpaceX was operating under NASA's rules and NASA had a safety window where the Falcon 9 could/couldn't fire its second stage.

The risk was almost certainly overstated, but NASA is understandably paranoid about things hitting the ISS.