That Darned Satellite

Unsurprisingly, the MSM is misreporting this – here’s what’s actually happening.

A crippled military observation satellite is expected to re-enter the atmosphere next month. That could be dangerous since about half of it will survive re-entry and hit the surface of the earth, including its thruster fuel tank containing hydrazine, a nasty poison.

So the US Navy plans to use an SM-3 ABM missile fired from the ship in the northern pacific to break the satellite into little bits, all of which will burn out in the atmosphere.

No doubt a subsidiary goal is to make clear to the Chinese, Russians et al that the US can whack their low orbit spy sateliites whenever it chooses.

The physics is quite straightforward. The earth’s atmosphere doesn’t just stop at a certain height, but thins out. My first and only satellite work was on one flying at 200 miles, and I had to compute the atmospheric drag so the thruster designers could figure out how much fuel they needed to keep it at altitude and pointing in the right direction.

Absent thrusters, or when they run out of fuel, low orbit satellites progressively decay to lower orbits until the atmosphere gets thick enough to heat them up (they move at about 15,000 MPH). The smaller the item, the quicker it burns up, since heating is a function of frontal area, and small objects have more area for their volume, so less volume to dissipate heat in.

Hence the breaking the target into smaller fragments.

The SM-3 is deployed on Aegis cruisers and destroyers, and its software currently assumes the target is an ICBM on a ballistic trajectory.

For the current task the developers will have modified the software to allow for the different characteristics of a satellite – which won’t be trying to dodge, and will be at a constant altitude during the intercept.

The trick is to hit it as just before it begins to start tumbling and burning up, while leaving enough time for another shot if the first misses:

Intercepting the satellite at about 130 nautical miles altitude will reduce the risk of debris in space. Once the satellite is hit, officials hope 50 percent of the debris will come to Earth in the first two orbits and the rest shortly thereafter…

That way the fragments don’t stay around in orbit doing damage (a flake of paint can go through a space suit at 15,000 MPH).

This will be a great test, and highly visible, so the software mod will probably be the most reviewed in the history of software development.


One Response to That Darned Satellite

  1. Crum says:

    Great post. This kind of post is what i was looking so far. It’s really hard to find this kind of post this day. thank you so much for the info. I’ll follow your next posts.

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