The U.S. Missile Defense Agency (MDA) intends to spend nearly $675 million from 2008 through 2011 to develop an experimental constellation of space-based missile interceptors that would launch in 2012, according to budget justification documents submitted to Congress in March.

There is no money for the so-called Space Test Bed in the MDA’s 2005 budget or in its spending request for 2006, reflecting a 2003 decision to put such activities on hold. But the documents show the effort roaring back to life starting in 2008 on a budget of $48 million. Program spending would rise to $150 million in 2009 and $248 million in 2010 before slipping back to $230 million in 2011, the charts show.

U.S. Air Force Lt. Gen. Henry “Trey” Obering, the MDA director, said at an April 11 conference here that there are no firm plans to deploy operational space-based interceptors, which would destroy ballistic missiles by crashing into them. But the potential of space-based interceptors is worth evaluating, he said.

The MDA also has tentative plans for a larger constellation of operational space-based interceptors that would launch starting in 2016, the budget documents show.

The Space Test Bed would draw on previous work including the MDA’s planned Near Field Infrared Experiment (NFIRE), Obering said during a speech here at the American Institute of Aeronautics and Astronautics’ 3rd Annual U.S. Missile Defense Conference . NFIRE, scheduled to launch in 2006 or 2007, is a test of sensors designed to distinguish between a rocket’s hot exhaust plume and the actual hardware.

The MDA plans to release a formal request for proposals for the Space Test Bed in early 2008, and award up to four concept design contracts later in the year, according to the budget justification material. One or more companies would be chosen to continue their design and development work in 2009.

The Space Test Bed would consist of five satellites and would be used for experiments including attempts to destroy medium- and intercontinental-range target missiles by ramming them, the budget documents show.

The program is likely to be controversial. Many on Capitol Hill and in the Washington think tank community oppose the deployment of space-based weapons in general, arguing that doing so would create a new arena for a costly and potentially dangerous arms race. Among the arguments against space-based missile defenses in particular is that they would create orbital debris that poses a threat to operational satellites, and that an effective shield would require an unaffordable constellation of thousands of interceptors.

U.S. Rep. Terry Everett (R-Ala.), chairman of the House Armed Services strategic forces subcommittee, has said the subcommittee will examine these issues in the course of classified briefings and in a public hearing on space weaponization.

Hugh Brady, a Democratic staffer on the House Armed Services Committee , said during a panel discussion at the conference that congressional debate over the Space Test Bed likely would heat up once MDA begins requesting significant funding for the effort .

Proponents of space-based interceptors dismissed concerns that such systems would do more harm than good. Among them is David Smith, chief operating officer of the Fairfax, Va.-based National Institute for Public Policy, who represented the United States during discussions with the former Soviet Union on defense and space issues from 1989 to 1991.

During a separate panel discussion, Smith noted that many critics of space-based missile defenses also predicted that there would be massive negative political fallout from the United States’ unilateral withdrawal from the 1972 U.S.-Soviet Anti-Ballistic Missile Treaty in 2001. So far, that has not happened, he said.

Steven Lambakis, a senior analyst at the National Institute for Public Policy, acknowledged during the discussion that destroying missile warheads in space might create debris. But space debris is infinitely preferable to having a U.S. city “turned into debris,” he said.

On the question of affordability, the MDA budget documents say the operational space-based system contemplated for 2016 would consist of 50-100 interceptors — far less than the thousands envisioned under the Pentagton’s now-defunct Brilliant Pebbles program. Lambakis said such a system would not break the Pentagon’s bank, especially given recent advances in miniaturization and other technologies.

In his speech, Obering said the space-based interceptors would constitute just one layer of a multi-tiered defense that includes the Ground-based Midcourse Defense system now being deployed and systems like the planned Kinetic Energy Interceptor. A Brilliant Pebbles-type constellation would only be necessary if the United States faced an adversary with a huge ICBM arsenal like the former Soviet Union, he said.

Such arguments did little to sway panel participant and outspoken space-weapons opponent Theresa Hitchens, vice president of the Center for Defense Information, a think tank here.

Hitchens cited a July 2003 study by the American Physical Society that found that a constellation of at least 800 to 1,600 interceptors would be needed to provide a limited measure of protection against just Iran and North Korea. The study assumed an attack scenario involving only one ICBM fired at the United States , she said. A far larger constellation would be needed to provide even a limited defense against a salvo of missiles , she said.