Satellite burns up following SpaceX rocket glitch • Hacker News Board

Re: Satellite burns up following SpaceX rocket glitch

#91

Post by ktizo » Sat, Oct 13, 2012, 1:40 PM UTC

ramidarigaz wrote: post #47

meepmorp wrote: post #39

Earlier quoted context omitted.

> And NASA doesn't have any reason to accept a risk that doesn't benefit its operations. Goodwill in the space community and helping to defray costs of future launches by making commercial launches more successful (and thus less expensive, if only for insurance purposes) seem like things that benefit their operations. Perhaps this is a naive opinion, though.

I agree, and I think NASA does too. They're just really conservative about the safety of the ISS (understandably so).

In risk terms, the satellite that was ditched is worth absolutely nothing compared to the ISS. The ISS is the single most important thing humans have in space at the moment.

Purely on the basis that the new trajectory can't be gone over with a pin, even if all the maths comes out saying that everything is lovely, you do not refire an ISS delivery rocket that is not where you expected it to be, especially one that has already sustained damage, just to test a new robot.

Re: Satellite burns up following SpaceX rocket glitch

#92

Post by mikeash » Sat, Oct 13, 2012, 2:02 PM UTC

ramidarigaz wrote: post #46

mikeash wrote: post #38

Earlier quoted context omitted.

No, the risky part was trying to raise the orbit using the F9 upper stage after it had burned more fuel than expected due to the failed engine. Quoth the article: > Falcon 9 had enough kerosene fuel left over to relight the engine, but the amount of liquid oxygen "was only enough to achieve a roughly 95 percent likelihood of completing the second burn, so Falcon 9 did not attempt a restart," I doubt many satellites h…

You're right. I remember them discussing attempting to raise the orbit with onboard fuel, but I doubt that was possible. My point was more that, prior to the engine failure, raising the orbit with the second stage was considered non-risky. You're correct that after the failure, raising the orbit with the second stage was risky.

Well, if you could assume that everything will work as expected, you wouldn't need insurance!

Re: Satellite burns up following SpaceX rocket glitch

#93

Post by InclinedPlane » Sat, Oct 13, 2012, 2:11 PM UTC

tsotha wrote: post #34

vl wrote: post #32

Earlier quoted context omitted.

It's unclear to me what is the risk to ISS. Secondary payload was on the much lower orbit, and even if it was on the same orbital plane, they could just slightly change orbit plane, and try to raise the obit with any chance of success entirely safe for ISS.

It's probably mostly a theoretical risk. On the other hand, I recall a flight to Mir that ended up slamming into the station. And NASA doesn't have any reason to accept a risk that doesn't benefit its operations.

There were no flights to Mir that "slammed into the station". The collision on Mir was due to an accident during testing of a new manual docking system for the Progress spacecraft. However, prior to the test the Progress had already successfully docked with the station, the test involved undocking and then switching to a new docking system for the test.

Re: Satellite burns up following SpaceX rocket glitch

#94

Post by gus_massa » Sat, Oct 13, 2012, 2:11 PM UTC

Dylan16807 wrote: post #79

sp332 wrote: post #76

Earlier quoted context omitted.

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.

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?

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

Re: Satellite burns up following SpaceX rocket glitch

#95

Post by rtkwe » Sat, Oct 13, 2012, 2:20 PM UTC

vl wrote: post #32

alanh wrote: post #3

Wow, I hope everyone reads the article before commenting. It’s still amazingly successful. There was a 95% chance the satellite would have made it if they tried, but they were obligated not to try if there were less than a 99% chance of success. (The reduced chance was due to the loss of one of the 9 engines.) And, of course, the primary mission to the space station was fully successful (the engine glitch notwithstan…

It's unclear to me what is the risk to ISS. Secondary payload was on the much lower orbit, and even if it was on the same orbital plane, they could just slightly change orbit plane, and try to raise the obit with any chance of success entirely safe for ISS.

Plane changes are one of the most expensive operations in an orbit iirc.

Re: Satellite burns up following SpaceX rocket glitch

#96

Post by EGreg » Sat, Oct 13, 2012, 2:33 PM UTC

ice cream!

Re: Satellite burns up following SpaceX rocket glitch

#97

Post by codex » Sat, Oct 13, 2012, 3:09 PM UTC

aeontech wrote: post #78

[deleted] wrote: post #69

Earlier quoted context omitted.

[deleted]

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…

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

Re: Satellite burns up following SpaceX rocket glitch

#98

Post by caycep » Sat, Oct 13, 2012, 3:20 PM UTC

so the ice cream bit at the end makes it all ok?

Re: Satellite burns up following SpaceX rocket glitch

#99

Post by aeontech » Sat, Oct 13, 2012, 3:36 PM UTC

dbaupp wrote: post #87

aeontech wrote: post #78

Earlier quoted context omitted.

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…

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.)

d'oh! thanks :)

Re: Satellite burns up following SpaceX rocket glitch

#100

Post by aeontech » Sat, Oct 13, 2012, 3:37 PM UTC

ordinary wrote: post #86

aeontech wrote: post #78

Earlier quoted context omitted.

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…

> 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( That's the same answer you came up with, so I guess you have t…

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