I hope that this message has not already been posted to the list. Apparently, while an ABM test conducted on a re-entry vehicle successfully destroyed the incoming warhead(s), a piece of space junk did a number on the discarded third stage of the ascent vehicle. The article was culled from: http://www.abcnews.com/sections/science/DailyNews/spacejunk0212.html By James Oberg Special to ABCNEWS.com Feb. 12 - A collision 240 miles above Earth last month has U.S. missile experts pondering the statistics of chance. The most likely explanation is "practically impossible," said one. =A0=A0=A0=A0 The third stage of a military missile launched from California apparently collided with a piece of space debris and was destroyed within range of sensors on Kwajalein Island, a small atoll in the western Pacific. =A0=A0=A0=A0 A modified Minuteman-II Intercontinental Ballistic Missile (ICBM) was launched from Vandenberg Air Force Base at 7:25 p.m. PST on Jan. 15. It carried a collection of targets and dummy warheads to test an anti-missile sensor on a missile to be launched from Kwajalein. That part of the exercise turned out successfully. =A0=A0=A0=A0= But half an hour after launch, and about a minute before it was to hit the atmosphere, the discarded third stage of the missile suddenly disintegrated into a cloud of shrapnel, which burned up in the atmosphere soon after. The fuel tank, about the size of a refrigerator, was falling at about 5 miles per second. A grapefruit-sized chunk of space debris was also zooming at about 5 miles per second on a collision course with the missile section. =A0=A0=A0= =A0 "Apparently it did collide with some piece of space junk,| said Lt. Col. Rick Lehner, a spokesman for the Ballistic Missile Defense Organization in Washington, D.C., the test's sponsor. =A0=A0=A0=A0 Enginee= rs reviewed data from radar screens and from telescopes on the aircraft tracking the missile. =A0=A0=A0=A0 "The scope clearly showed a small objec= t moving rapidly from in-range to out-range," said a witness who didn't want his name used. "When its range coincided with the tank, it disappeared and the tank slowly changed from a single object to a cloud of targets." Differing Data The tracking data, however, is ambiguous to some space debris experts within NASA. One radar that tracks larger objects saw only the fuel tank, while a radar using frequencies better suited to small objects saw both the tank and the "intruder." =A0=A0=A0=A0Although the visual reco= rds, which have not been released, show a streak approaching the tank horizontally, there's no way to determine whether the streak was at the same altitude as the fuel tank. =A0=A0=A0=A0Don Kessler, formerly NASA= 's guru on space debris, says a collision is certainly possible. "But it's one of the least probable kinds of collisions you could expect." =A0=A0=A0=A0 "I would look very strongly for something else," he says. "Ev= en a very rare internal explosion combined with a coincidental fly-by of an unrelated object is numerically much more probable than an actual collision." =A0=A0=A0=A0 The U.S. Space Command tracks about 7,000 objects= in Earth orbit bigger than a few inches across, many of them fragments of rocket explosions. But all attempts to correlate this object with any catalogued space junk have been unsuccessful. =A0=A0=A0=A0"They don't know what it was," Lehner says. =A0=A0=A0=A0 Many thousands of even-smaller pie= ces are known to be circling Earth, but they're too small for accurate tracking or even detection. =A0=A0=A0=A0 In recent decades, concern has gr= own that space junk could pose a hazard to satellites, even manned space vehicles. Space experts believe that collisions are rare; most spacecraft failures-even those in which a collision is initially suspected-are caused from within. Shuttles Steer Clear On half a dozen occasions over the past decade, space shuttles have altered their flight paths to avoid predicted collisions. But these precautions were probably not really necessary. The Russian Mir space station, in orbit since 1986, has had a few tiny impacts and a few close calls, but has suffered no real damage from space junk. =A0=A0=A0=A0 Citing decades of flights, experts consider the odds of a missile on a half-hour flight actually hitting something in space to be exceedingly remote, and they're reluctant to believe it could have happened. The other explanation is even more worrisome-a coincidental explosion of a third stage might point to a defect that other missiles may have. =A0=A0=A0=A0Although the probability of a bizarre combination of other circumstances-a self-induced explosion from leftover fuel combined with an unrelated space junk fly-by-may actually be much less unlikely, the Defense Department seems satisfied it was a freak accident that will probably never happen again. James Oberg spent 22 years as a rocket scientist for NASA, and has written eight books and numerous articles on space flight, He became an ABC News consultant in mid-1997.