RE: Milstar 3 Centaur (was Unidentified subject!)

Ted Molczan (
Sat, 22 May 1999 11:57:47 -0400

The orbit posted by Anthony Beresford:

1 99010U          99139.43272912  .00000000  00000-0  00000+0 0    02
2 99010  28.3800 241.2335 2130000  63.6428 296.3566  9.66794000    05

is in excellent agreement with the circumstances of the Milstar launch from
Cape Canaveral on 30 Apr 99, at 16:30 UTC.

The mean motion suggests that this is the Centaur stage, not the Milstar.

The original Milstar orbital dimensions, 741 x 5000 km, released by the U.S.
Air Force soon after the launch, were consistent with a mean motion of about
9.77 rev/d. According to the USAF, during 6-10 May, Milstar's propellants
were gradually burned off, which raised its orbital dimensions to 1096 x
5150 km, consistent with a mean motion of 9.38 rev/d. Since the orbit of the
object discovered by the Australians is somewhat lower, it must be the

Interestingly, the Centaur's orbital elements appear to confirm that the
bright cloud observed from Sesfontein, Namibia (13.65 E, 19.12 S) on 30 Apr
99, at about 19h UTC, was indeed the Centaur, venting its remaining
propellant. An ephemeris shows that during the period 19:00 - 19:10 UTC, the
Centaur was very near the sky location described by the Namibian observers.

The one flaw in the Namibian sighting is that they reported the cloud was
stationary for about 20 minutes, which seems impossible. Perhaps they were
so entranced by the sight, that it seemed to last longer than it really did.

Ted Molczan