20 February 2009

Spacecraft Missions Play Dodgeball with Orbiting Debris

U.S., Russian officials consult after recent collision of satellites

At any given moment, thousands of pieces of debris orbit the earth, as depicted in this European Space Agency computer-generated image.

By Jacquelyn S. Porth
Staff Writer

Washington — Tens of thousands of pieces of space debris, or space junk as some call it, orbit the earth, threatening to disrupt space travel and destroy communications satellites on which the world depends.

Using a global network of space surveillance radars and optical sensors, the U.S. Joint Space Operations Center has catalogued 18,000 man-made pieces of debris that are larger than a baseball. (Smaller pieces, though not tracked, can cause considerable damage.)

The field of debris became larger February 10. An active commercial U.S. Iridium 560-kilogram (1,200-pound) satellite collided with an out-of-commission 950-kilogram (2100-pound) Russian military Cosmos satellite 500 kilometers (310 miles) above Siberia.

U.S. Marine General James Cartwright, vice chairman of the Joint Chiefs of Staff, said the new debris cloud will likely require spacecraft operators to “play a little bit of dodgeball.”

NASA scientist Nicholas Johnson said the February collision may have created thousands of pieces of debris a centimeter or a millimeter in size. NASA’s Orbital Debris Program Office in Texas plays a lead role in developing measures to protect assets in orbit. Controlling the growth of orbital debris is a key NASA priority.

The Defense Department is busy analyzing the paths of the new debris — a process that could take weeks. Cartwright said the good news is that once the debris paths stabilize in a month or two, most orbits will be predictable enough to be avoided by space and satellite missions.

But the data-processing capability of the military’s Joint Operations Space Center, in Nebraska, is insufficient to prevent all satellite collisions. For now, the priority is protecting manned spaceflights.

The center did not have warning of this collision, but learned of it when contacted by Iridium. Risk to the International Space Station is deemed to be low because the station and the debris are not in the same orbit.

MITIGATING NEW THREATS

The satellite collision is believed to have been the fourth such occurrence, but scientists say collisions could become more frequent as space assets continue to proliferate. Space is getting crowded — there are an estimated 13,000 satellites now in orbit.

The United States removed one of its dead National Reconnaissance Office satellites from space in February 2008. The satellite’s fuel tank was destroyed without incident. Residual debris circulated briefly in low orbit, but then re-entered earth’s atmosphere within weeks.

China created waves of debris in January 2007 when it destroyed an old satellite with a missile. U.S. Air Force Lieutenant General William Shelton, the commander of the Joint Functional Component Command for Space, told members of Congress that the Chinese anti-satellite test put 2,300 pieces of debris into orbit, creating a hazard to manned and unmanned space flight.

Because of increasing crowding in space, Cartwright called for greater international information sharing about satellite activities and orbiting debris.

The United Nations Committee on the Peaceful Uses of Outer Space convened in Vienna to discuss the issue of how to reduce threats from space debris shortly after the February 10 satellite collision.

The European Space Agency had created its own space debris monitoring system in January.

The United States has been active in trying to identify potential space hazards. Garold Larson, who heads the U.S. delegation to the Conference on Disarmament in Geneva, said the United States does all it can “to preserve safety of flight in the complex environment of outer space.” He told conference members February 19 that the satellite collision underscores the problem of an “increasingly congested space environment.” Collisions, he said, could limit the use of space by researchers and scientists.

U.S. and Russian officials have been in consultation since the collision occurred, Larson said, providing “a valuable transparency and confidence-building measure” between the two countries. Future cooperation with other countries will help prevent further collisions.

The space coordinates for the new U.S.-Russian satellite debris will be posted on the public Web site http://www.Space-Track.org. Defense Department spokesman Geoff Morrell said this will enable spacefaring nations and entities “to determine the risk to their space assets.”

The full text of Larson’s statement is posted on the Web site of the U.S. Mission to the Conference on Disarmament.

For more information on U.S. space policy, see “Protecting Space Environment Remains a Critical U.S. Interest.”