The Multi-Service Launch System booster was launched from Vandenberg Air Force Base, Calif. at 7:25 Pacific Standard Time Jan. 15. Its impact with orbital debris apparently occurred approximately 30 minutes later over the Pacific Ocean near Kwajalein in the Marshall Islands.

Reports of the apparent collision have circulated on the Internet in recent weeks.

Lt. Col. Rick Lehner, spokesman for the BMDO at the Pentagon, confirmed the incident in a telephone interview Feb. 12. "Apparently, it did collide with some piece of space junk, he said. "It was after third-state separation and did not affect the actual mission."

Others were not ready to conclude that space junk was the problem.

"It's certainly a possibility. But it's one of the least probable kinds of collisions you could expect," Don Kessler, a retired space consultant and former space debris expert with NASA, said Feb. 13.

"I would look very strongly for something else. Even a very rare internal explosion combined with a coincidental fly-by of an unrelated object is numerically much more probable that an actual collision," he said.

This was the third test flight in the BMDO's Integrated Test Flight program to evaluate Anti-Ballistic Missile sensors. Nine target objects were deployed from the missile. An Exoatmospheric Kill Vehicle carrying a test sensor was launched aboard a Payload Launch Vehicle from Kwajalein in an attempt to detect the targets.

BMDO officials will attempt an actual intercept during a fourth test flight planned for September, Lehner said.

According to several sources on Kwajalein, who stressed that the information had never been classified, the refrigerator-sized third-state tank was behaving as expected when it suddenly disintegrated shortly before hitting the atmosphere.

Its altitude at that point was slightly above 320 kilometers.

"The scope clearly showed a small object moving rapidly from in-range to out-range," Michael Minardi, an employee of Massachusetts Institute of Technology's Lincoln Laboratories, reported in late January. "When its range coincided with the tank it disappeared and the tank slowly changed from a single object to a cloud of targets." Laboratory employees operate the Altair tracking radar under contract to the Department of Defense.

U.S. Space Command analysts used radar tracking and visual tracking date to attempt to explain the event. Imagery from the Airborne Space Track aircraft, a modified Boeing 767 based in Seattle, showed what looked like a tiny streak, on what was nearly a collision course. The streak vanished when it reached the same location in space as the third state of the Multi-Service Launch Vehicle. On the Altair tracking radar, the object showed up in ultra-high frequency but not in very-high frequency, suggesting it was small in size, perhaps 12 to 15 centimeters across, according to a source on Kwajalein.

The tracking data on the object was not sufficient to compute an orbital path, a NASA source said.

All attempts to correlate the object with the more than 8,000 cataloged space objects were unsuccessful. "They don't know what it was," Lehner said.

But because of its apparent small size, the fact that it could not be found in the catalog came as no surprise, according to space debris experts within NASA.

However, Space Command suspicion centered on an uncataloged piece of Pegasus booster debris.

The upper state of a Pegasus rocket exploded in orbit in June 1996 two years after being used in the launch of a U.S. Air Force satellite. The explosion created 700 pieces of trackable orbital debris, posing a potential threat to NASA spacecraft including the space shuttle and Hubble Space Telescope, an FAA official told SPACE NEWS in December.