Spy sat to come home… not too secretly

Bad Astronomy
The entire universe in blog form
Jan. 28 2008 12:00 PM

Spy sat to come home… not too secretly

The news is buzzing that due to a loss of control, a US spy satellite is going to re-enter the Earth's atmosphere sometime in February or March.

This sucks, for many reasons. Obviously, it's one less piece of equipment that will gather intelligence Bush will ignore.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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Haha! That one was for the weenies who hate it when I make political comments.

But seriously, besides the loss of an important tool, the loss of control over the satellite means it cannot be guided in for a safe re-entry over an ocean. Satellites, especially big ones (this one is reported to be maybe 10 meters long) don't completely disintegrate when they come back in. They break apart, and some pieces can survive. This includes very dense parts (like, say a telescope mirror) which can withstand re-entry, and ironically, very light pieces, which slow down so rapidly that they don't have enough time to burn up. They slow to a few hundred kph and then just fall the rest of the way.

These lighter pieces include fuel tanks, which are large and hollow. This particular satellite may have used hydrazine as a propellant, which is toxic. Having some of that in a leaky fuel tank hitting the ground is not a great scenario.

However, I think it's unlikely that it'll hit anyone or damage property. The Earth is still 70% or so ocean, so right away the odds of hitting land are 30% at best. Moreover, most of the land on this planet is unpopulated, and where it is populated, it's mostly lightly populated. However, this doesn't mean the odds of it doing something bad are 0; a Soviet satellite came down in Australia a few years ago. I'd much rather know this thing will burn up over the vast area of the Pacific ocean.

Of course, the government isn't really talking, since this was a secret mission. It's possible more info will leak out, so stay tuned here or at UniverseToday for more info.