Satgen625 Don't Shoot. Friend by GM4IHJ (BID SGEN625) 2001-03-17 For some time now professional and amateur observers have been trying to compile a catalogue of asteroids which just might come into earth orbit and, one day, collide with the planet. A collision , which if the asteroid were to be big enough, could result in almost complete destruction of life on earth. As happened 65 million years ago ,in the asteroid collision event credited with destroying the dinosaurs. On February 18th 2001. A fast moving object was spotted by observers using a 36 inch telescope operated by the Arizonan Space Watch team. Further sightings of the object on subsequent days suggested that it was a small object in a near earth orbit around the Sun. An orbit which was bringing it within 580,00 kms of the earth on the 23rd of February. The object was assigned a temporary designation of 2001 DO47, by the Harvard Smithsonian Minor Planet Centre. But it quickly became clear that it was not quite that simple. The object was certainly small 10 metres or less, but it was not following the predicted orbit. Sometime on or around Februry 23rd it speeded up, and was thereafter getting well ahead of predictions. Suggesting as one observer remarked , " that it had switched on its engine". Two days later NASA confirmed that the target was friendly. The NASA solar WIND probe had indeed been in that part of the sky and it had just used its engine to initiate an orbit change. Launched in 1994, WIND is a lonely wanderer. Journeying out towards Lagrange point 1 nearly 1 million miles sunward of the earth, at one time. It has also looped high above the plane of the earths orbit round the Sun, on a mission to measure solar wind and magnetosphere parameters , sunwards of earth, antisunwards and high up in the magnetosphere above the earths poles. On rare ocassions its wandering brings it back closer to the earth and the moon. So it will undoubtedly be seen again by Spacewatch. A situation which has prompted the Minor planet centre, to put information relating to the orbits of both WIND and the dozen or so other satellites which wander far from earth, into its computers. All of which suggests that the Spacewatch observers are doing an excellent job, locating and tracking an object as small as the 2.5 metre diameter WIND. Anything less than 10 metres in diameter should pose no serious threat if it enters the earths atmosphere. So Spacewatch should spot the bigger more dangerous objects much further away, provided they have enough telescopes for all round tracking. Note. Mir is now responding to the denser atmosphere . Altitude is reducing quite quickly with a re entry somewhere around 17th March 2001 looking likely. To the questioner who asked where is its perigee low point occuring. The answer is that the atmosphere has almost circularised the orbit . So perigees and apogees are not really important any more.