Friday, 15th February 2008

Shooting Down Satellites

2:58pm As is all over the papers today the US has announced that it's interested in shooting down one of their old satellites. All motivated by the health dangers of those of us sitting down here, oh yes, really:

The multi-million dollar craft is due to re-enter Earth's atmosphere next month after spiralling out of control shortly after launch in 2006.
Weighing 5,000lb, L21 is fitted with thruster engines which contain a toxic rocket fuel called hydrazine.

Defence officials said they feared that the fuel could kill if it was released into the atmosphere on re-entry.

"What makes this case is a little bit different is the likelihood that the satellite could release much of its 1,000-plus pounds of hydrazine fuel as a toxic gas," said James Jeffries, the Deputy National Security Adviser.

No, no, really, that is the reason they're giving. There couldn't be any truth at all to the rumour that the entire military establishment has been gagging for a chance to try out part of the Star Wars catalogue, shooting down a satellite. Oh no:

However, some experts believe the risk is minimal and that the US wants to test out its missile-defence system.

No, perish the thought. No, really, we all do believe the US Government don't we? Just as we trust our own Lords and Masters? As the US Government actually says:

Accidental discharge into water, air, and soil may occur during storage, handling, transport, and improper waste disposal. However, hydrazine rapidly degrades in the environment and is rarely encountered.

They also note that most common method of exposure is via smoking. Or as the WHO says:

Assuming an average hydroxyl radical concentration of 106 radicals/cm3 for the lower troposphere, the half-life of hydrazine with respect to this radical is estimated to be about 3 h (Harris et al., 1979; Pitts et al., 1980). Assuming an average level of 80 µg ozone/m3 air (Singh et al., 1978), the lifetime of hydrazine with respect to ozone would be approximately 1 h. Nitrogen dioxide also reacts with hydrazine (Pitts et al., 1980; Tuazon et al., 1982). In a polluted atmo- sphere, the lifetime would be of the order of minutes (Pitts et al., 1980; Tuazon et al., 1982; Schmidt, 1984).

To put that more plainly, if it burns up on re-entry, there's no problem, if it hits the ground in one piece then being under that one piece could be a problem but the hydrazine won't be.

Nice try Mr. Jeffries, but come on, own up, you boys just want a chance to play with your very expensive toys, don't you?