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A comment on SpaceX Falcon 9 – Possible Explosion.

Re:SpaceX Falcon 9 – Possible Explosion by tomp on Tuesday October 01, 2013 @07:04AM (#6475340)
Assuming this is true, and there actually was an explosion, and it was caused by the SpaceX rocket: I wonder how does this amount of space debris impact and potentially endanger future orbit flights. As much as I support technology development and private space exploration efforts, I think that private companies shouldn't be allowed to pollute the orbit without retribution. I hope they figure out the cause, and fix it, and not simply cover it up.
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Re:SpaceX Falcon 9 – Possible Explosion by VLM on Tuesday October 01, 2013 @09:34AM (#6475968)
Weirdly enough in the long run you want to blow up stuff to keep orbits clean. MUCH better surface to volume ratio means faster de-orbit. This is a classic short term vs long term thinking problem. In the short term you're better off with fewer trackable objects but in the long run you're better off with no trackable objects at all.

If you're really bored you can run calculations on deceleration vs mass per surface area. From memory there are (admittedly extremely low) orbits where a rail-car shippable steel construction I-beam, actively pointed end-on, will orbit for months but a hot air balloon would deorbit in less than one full orbit.

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Re:SpaceX Falcon 9 – Possible Explosion by tomp on Tuesday October 01, 2013 @12:59PM (#6477414)
Aren't there better solutions? For functional satellites, of course, you could just de-orbit them (so that they burn while re-entering the Earth's atmosphere), but even for passive objects, maybe you could steer them so that they start falling towards the earth. The Wikipedia article on Kessler Syndrome[1] suggest using lasers, but I guess other ways are possible: if you intend to "blow them up", you might as well redirect the rocket to explode slightly above the orbiting object, so that it is not damaged, but only pushed towards the Earth.

[1]: http://en.wikipedia.org/wiki/Kessler_syndrome

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Re:SpaceX Falcon 9 – Possible Explosion by VLM on Tuesday October 01, 2013 @02:50PM (#6478269)
There are some orbital mechanics problems. You can't "steer" in orbit. Shoving down at any sane rate results in going up half an orbit later. The best place to blow it up would be in front of it. A couple hundred m/s is all it takes in some cases.

There's a free windows only game called Orbiter under continuous (ish) development since early 2000s. Its informative about the weird truths of orbital dynamics. Several years ago I went thru a phase of flying between Jupiters moons for fun.

There's probably a startup idea in creating what amounts to a E6B for orbital mechanics. The problem is making it elegant and easy to use. Anybody can open matlab/octave/mathematica/whatever and say "just enter a bunch of equations". I'm not sure the MFDs in orbiter are the wave of the future either. And its easy to get sucked into the trap of making it too simple for the .edu market such that it can't actually simulate anything. Its a hard problem. Maybe more for a PHD project because I'm mystified how to monetize.

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Re:SpaceX Falcon 9 – Possible Explosion by toomuchtodo on Tuesday October 01, 2013 @02:41PM (#6478197)
One day we're going to need Kessler Cleaners in high geosync orbits to use lasers to "encourage" debris to deorbit.
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Re:SpaceX Falcon 9 – Possible Explosion by swatkat on Tuesday October 01, 2013 @07:49AM (#6475491)
> As much as I support technology development and private space exploration efforts, I think that private companies shouldn't be allowed to pollute the orbit without retribution

Yes; even governments shouldn't pollute orbits. One such example:

http://en.wikipedia.org/wiki/2007_Chinese_anti-satellite_mis...

http://i.imgur.com/QmWXjCP.jpg

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Re:SpaceX Falcon 9 – Possible Explosion by kristaps on Tuesday October 01, 2013 @07:06AM (#6475349)
Have you heard of the Kessler Syndrome? (http://en.wikipedia.org/wiki/Kessler_syndrome)
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Re:SpaceX Falcon 9 – Possible Explosion by JshWright on Tuesday October 01, 2013 @08:12AM (#6475590)
That's a very big assumption at this point. There is no evidence whatsoever that an explosion occurred.

There were numerous reports of visual phenomenon consistent with the vehicle simply venting its fuel. The resulting gas cloud from such an event often results in inaccuracies in tracking.

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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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