Even with Robert Gates “pulling the trigger,” it wasn’t about the tank of hydrazine, a health hazard only if it hit the ground intact. There’s no way a fuel tank built for Earth orbit is going to survive an atmospheric reentry intact.
Unless it wasn’t built for orbit. Like it was a bomb or something. But I don’t think so.
I have no idea why the feds and the military waited till now to shoot down their brain-dead spy satellite, but it’s an easy speculation that it wasn’t the noxious fuel they were worried about.
The physics of it is simple. You have an object travelling at about 17,000 mph hitting the Earth’s upper atmosphere. It starts rolling, tumbling, shaking, and heating up. You have something like the space shuttle, designed to withstand high temperatures and stress of slowing down from 17,000 to 200 in a matter of minutes. A little nick on the wing will do it in, as it tragically did in 2003.
A fuel tank on a spacecraft is designed for one thing: to hold the fuel until it runs out. Tanks are built to be lightweight. Any kind of hit from orbital space junk or a micrometeor is going to breach most anything we can build, so there’s no real point in wasting materials on making it thick or something.
Looks like the military hit the target, though. Nice aim. Does it worry other nations who wonder about their satellites getting shot down?