SpaceX Falcon 9 – Possible Explosion

Re:SpaceX Falcon 9 – Possible Explosion by bbx on Tuesday October 01, 2013 @07:21AM (#6475400)

I always wondered what the odds were of such a collision occuring in space. I realized that the surface of the orbit area is way larger than the Earth's surface. So I imagined satellites and debris located on and moving around the Earth's surface, and wondered what the odds were of them colliding in such a situation. I imagined they'd be extremely low, making the odds of a space collision even much lower.

Not sure I explained it clearly, and it might be a wrong assumption, so feel free to enlighten me.

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Re:SpaceX Falcon 9 – Possible Explosion by throwaway_yy2Di on Tuesday October 01, 2013 @08:06AM (#6475561)

Surprisingly large. This isn't accurate even to within an order-of-magnitude: it's just to get some insight. The surface of the earth is (to the nearest power of 10) ~10^9 km^2. LEO satellites go up ~10^3 km, so that's ~10^12 km^3 of volume for them. A satellite traverses ~10^8 km/year (that's a lot!), so if it has ~10 m^2 cross section (10^-5 km^2), its path encompasses a volume of ~10^3 km^3/year. Under some simplifying assumptions, the probability of two arbitrary satellites colliding is something like ~(10^3 km^3/year / 10^12 km^3) = 10^-9/year. There's ~10^4 satellites, and the rate of collision goes as the number of pairs of satellites ~N^2, so the rate at which any two satellites collide is (10^4)^2 * 10^-9/year = 10^-1/year or once per decade.

I think the particularly "unintuitive" parts of this are, one, the incredible distances travelled when you sustain Mach 20 for years (10^8 km/year); and two, the quadratic scaling (10^4*10^4).

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Re:SpaceX Falcon 9 – Possible Explosion by antubbs on Tuesday October 01, 2013 @08:01AM (#6475543)

So, it's certainly happened:

http://en.wikipedia.org/wiki/2009_satellite_collision

I'm nowhere near talented enough to talk in terms of "odds" with respect to satellite collisions, but it's worth noting that certain orbit geometries are going to naturally see a lot more density because several satellites want to be in a somewhat similar orbit for various reasons.

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Re:SpaceX Falcon 9 – Possible Explosion by swatkat on Tuesday October 01, 2013 @08:10AM (#6475583)

Another one:

http://www.space.com/20146-russian-satellite-space-junk-thre...

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Re:SpaceX Falcon 9 – Possible Explosion by DanBC on Tuesday October 01, 2013 @09:46AM (#6476053)

NASA has some nice pages about orbital debris. They inspect everything when it comes back to Earth to check for impacts, and they have photographs of micro impacts.

(http://orbitaldebris.jsc.nasa.gov/)

Site might not be available because US politics is batshit insane.

The photo gallery has some images of debris impacts. These micro impacts seem to be really common. The amount of debris is pretty large.

> More than 21,000 orbital debris larger than 10 cm are known to exist. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles smaller than 1 cm exceeds 100 million.

The surface area of Earth is about 510 million square kilometers.

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