- 12:02 15 February 2008
- NewScientist.com news service
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The planned destruction of a disabled US spy satellite will create hundreds of thousands of marble-sized fragments, some of which could strike the International Space Station (ISS), although experts are divided about the risk.
The Pentagon cites concern about contamination from toxic hydrazine fuel as the main reason behind the decision to shoot down the satellite rather than let it disintegrate in the atmosphere.
But the decision worries David Wright, co-director of the global security programme at the Union of Concerned Scientists in Cambridge, Massachusetts, US.
"It sounds to me like a bad idea," Wright told New Scientist. "This satellite is about two-and-a-half times as massive as the Chinese satellite destroyed last year, so you would expect to get a lot more debris."
The Chinese anti-satellite test, performed in January 2007, was conducted about 850 kilometres (528 miles) above the Earth, where the atmosphere is thin and objects experience less drag. Debris from the Chinese test is expected to remain in orbit for years or even centuries.
In contrast, the current plan for shooting down the US National Reconnaissance Office (NRO) satellite involves firing a modified navy missile at the spacecraft while it is about 240 km (150 miles) above the Earth. The atmosphere is thick enough at that relatively low altitude that most of the debris will be dragged down and disintegrate in a matter of hours or days.
However, Wright worries that some of the debris from the explosion could get kicked up to a higher orbit, where it could pose a threat to the ISS, which orbits the Earth at about 340 km (211 miles).
"These high-energy explosions are very hard to describe and understand in detail," Wright says. "How certain are they about what the debris consequences are?"
Donald Kessler, a retired manager of NASA’s Orbital Debris Office at Johnson Space Center, also worries about the debris but thinks the possibility of contamination from hydrazine is worse.
"When you're dealing with a chemical like that, it's a different ball game,"Kessler told New Scientist.
Max Meerman, a satellite engineer at the MDA Corporation in Vancouver, Canada, believes that concerns about debris are overblown. "The satellite will be slowed down when it flies into the missile, so most bits from the impact will slow down, rather than speed up, and re-enter [Earth's atmosphere] even quicker," he says.