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If the sky falls, can we shoot it?

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8 December 2011 11:31

Dr Morris Jones, who has written previously for The Interpreter, is an Australian space analyst.

Some time in January 2012, Russia's Fobos-Grunt spacecraft will fall back to Earth. The probe was launched in November 2011 on a sample-return mission to the Martian moon of Phobos. However, the spacecraft malfunctioned soon after launch and became stranded in Earth orbit.

The impending doom of Fobos-Grunt is the latest in a string of well-reported spacecraft re-entries. Such events are likely to become more frequent as more objects are launched into space. But could we one day shoot them down, rather than just await their impact?

From the perspective of international law, spacecraft re-entries and impacts are straightforward events. The 1967 Treaty on the Peaceful Uses of Outer Space is a well-crafted document, widely ratified and respected. Basically, a nation responsible for putting something up also bears responsibility when it comes down.

This has resulted in compensation claims, such as the time NASA was fined by an Australian council for littering after debris from Skylab fell to earth. A more notorious event was the re-entry of the Soviet Union's Cosmos 954, a nuclear-powered satellite that scattered radioactive debris over northern Canada. This required a substantial recovery and clean-up effort.

In recent months, we have witnessed the downfall of a NASA atmospheric research satellite and a German astronomical satellite that re-entered without incident, despite media scaremongering. In fact, objects fall from orbit almost every day, without much attention. Fear and uncertainty arises with some of the satellites for technical reasons. It's very difficult to say when or where a falling spacecraft will land.

Issues with atmospheric density and the aerodynamic properties of the satellites make reliable guesses almost impossible. This results in vague assurances from officials that the probability of someone being injured is very low, but not impossible. The inability to predict or control the re-entry is frustrating to emergency response teams as well as those who must account for any potential damage. Basically, the whole world must go on a partial alert.

In boffin circles, there's a growing interest in destroying these objects with anti-satellite (ASAT) weapons. ASAT systems have been tested by Russia and China. However, it's generally agreed that only the US possesses a true, operational ASAT capability.

ASAT was recently used to destroy an incoming US spy satellite. The official explanation for the ASAT attack was to prevent toxic fuel from posing a hazard after impact. However, this author also suspects that the US Government wished to avoid fragments of this advanced satellite falling into hostile hands.

Despite the potential benefits, ASAT interceptions of rogue satellites are highly controversial. Strategic doves bemoan a potential arms race in space. There's also the thorny question of a potential ASAT attack against a rogue satellite launched by another nation. Doing so without the consent of the satellite's owner could be more than mildly unsettling. Nations without this capacity could feel extremely reluctant to ask America to shoot down their own spacecraft, for political, strategic and diplomatic reasons. Don't expect Fobos-Grunt to be hit by a US missile.

Above, NASA's Upper Atmosphere Research Satellite, which re-entered earth's atmosphere late September 2011. Photo by Flickr user NASA Goddard Photo and Video.

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