Space War

July 29, 2013. SY-7 Launch. Xinhua Photo.

Rumor has it that China is playing with anti-satellite weapons. This might prove to be unintentionally disastrous. China "shot down" one of their own satellites a few years ago by colliding a chunk of iron (or strawberries, anything would do) with the satellite. The collision vaporized both the target and the weapon. Okay, vaporized might not be quite accurate. The smash up broke both boxes into clouds of small pieces that essentially continued on their merry way: in orbit, where they will stay for the next umpteen years destroying anything they run into.

3/8" steel plate with 30 caliber bullet holes

Bullets can make mince meat out of iron plate, and rifle bullets only travel about 1/2 mile per second. Satellites are travelling 5 miles per second. Now you might think that is not such a big deal, I mean, velocity is directly related to altitude, and all the satellites are all going the same way, so anything close enough to collide should be going just about the same speed. Well, yes and no (my new favorite phrase). If all orbits were circular and going around the equator, then yes, there should be no problems. That's how we manage to keep so many geosynchronous communications satellites (over 200) in orbit simultaneously.

Debris field from Chinese anti-satellite missile test five minutes after impact (simulation).

Not all orbits are at the equator. The one in the picture is a polar orbit, it goes over the poles. Not all orbits are circular. Spy satellites sometimes dip down as low as 70 miles in order to get a better view, then go back up to 100 or so where there is less air resistance (we're talking molecules per cubic foot here). Both the US and Russia use the Molniya orbit in order to get more hang time over Russia (the US for spy satellites, the Russians for communications). Geosynchronous orbits don't work so well for locations on Earth at high latitudes. The Molniya orbit varies in altitude from a high of 25,000 miles to a low of grazing the tops of the Andes Mountains. The velocity likewise varies from a low of one mile per second at apogee (that's the high point) to a high of six miles per second at perigee (that's the low point over South America).

    The Fermi Gamma-Ray Space Telescope had a near miss (30 milliseconds, or less than 1,000 feet) with a derelict satellite a few years ago (the 4:37 mark in the video).