TDF-1 is slowing down

Matson, Robert (ROBERT.D.MATSON@cpmx.saic.com)
Wed, 25 Aug 1999 13:03:05 -0700

Hi All,

Got some real good timing data on TDF-1 (#19621) last night.
This satellite is definitely slowing down.  In two days the
period has increased from 29.666 +/- .006 to 29.804 +/- .002,
an increase of .07 seconds per day.  This compares favorably
with Rick Baldridge's period measurement on August 17 (UT)
of 29.24 seconds:

Aug 17  29.24
Aug 23  29.666   + .426/6 = .071
Aug 25  29.804   + .138/2 = .069

So by Aug 28, the period will be just over 30 seconds,
increasing by a little over 2 seconds per month.

Incidentally, the center of last night's (Aug 24; Aug 25 UT)
peak for my location in southern California was about 6:06 UT,
5 minutes later than what I had predicted.  So my spin axis still
needs some work.  The pointing normals I have so far span less
than 2 degrees (with a fair amount of uncertainty on those
points), so the 5-minute error is not surprising.  Only more
data points (preferably from geographically separated regions)
will improve the model.

PPAS report for TDF-1 (19621, 88098A):


88- 98A 99-08-25 06:13  RM 730.20 0.05 24.5 29.804 mag +2 -> inv