The US Missile Defense Agency (MDA) wants $10 million to investigate space-based weapons over the next year. As Pentagon budgets go, it is small change, but it is also a red flag for critics who worry that such plans could turn space into a shooting gallery.

Most of the $8.9 billion the Bush administration plans to spend on missile defence over the next year will go towards developing systems based on the ground, at sea, or in the air.

These defences "could be greatly enhanced", however, by adding space-based interceptors, Lieutenant General Trey Obering, head of the MDA, told the House Armed Services Committee on Tuesday.

The US plans to use multiple systems to defend against attacking missiles. These will attempt to intercept missiles at different stages during launch, mid-course flight, and as it approaches a target. So far, however, only one layer has been tested at a time, and with mixed results.
Airborne Laser

Fifteen mid-course interceptors have been installed in Alaska and California, but progress has been slow on developing systems that attack missiles during the boost phase, when they are easiest to spot and most vulnerable. The Airborne Laser is one such system, but it will not be tested until 2009. That is several years behind schedule and its range is also limited to a few hundred kilometres.

Space-based interceptors promise a much broader reach, Obering says. "Space systems could provide on-demand, near global access to ballistic missile threats," he told Congress.

The "Space Test Bed" is not in the 2007 budget, and Obering testified that the $10 million requested for next year would be used "to begin concept analysis and preparation for small-scale experiments".
Classified budget

However, the programme could be bigger than advertised, says Sam Black of the Center for Defense Information, in Washington DC, US. "My suspicion would be that there's black money (from the classified part of the budget) going into it," he told New Scientist.

In a report published online on 21 March, Black notes that the Bush administration originally planned to spend $1.2 billion on space-based interceptors between 2002 and 2007. This did not happen and, since then, public plans for space weapons have become less clear.

An MDA spokesman insists the space program is "a very small thing for studies, modelling and simulation". But Black worries that the Pentagon may be further along in developing such technology. "We would like to see a debate before they go ahead and put something in orbit," says.