Mir close encounter

Matson, Robert (ROBERT.D.MATSON@cpmx.saic.com)
Tue, 27 Jul 1999 11:35:39 -0700

Hi List,

I've discovered another upcoming close encounter -- this time with Mir.
The encounter is with GPS 2-23 r1 on 28 July at 22:59:10 UT -- about
29 hours from now as I type this.  Here is the COLA output for the
encounter:

   Date     UTC Time   Norad Satellite Name   Range/OrbSep  NdAng EphAge
 7/28/1999 22:59:09.81 22878 GPS 2-23 r1        6.5/   0.1   91.0  +5.48

I've been following this one for a few days, and with each new Mir
element set, the minimum range is going down.  But the number to pay
attention to is that 0.1-km orbital separation!

The Mir elements are quite fresh.  What I need are more up-to-date
orbital elements for #22878.  The ones used for this prediction will
be over 5 days old by the time of tomorrow's encounter.  Here's what
I used:

Mir Complex
1 16609U 86017A   99208.11641024  .00029703  00000-0  21123-3 0  7105
2 16609  51.6593 139.3393 0006657 356.4393   3.6453 15.73587156767695

GPS 2-23 r1      5.9  2.4  0.0  5.0 v 12.6
1 22878U 93068B   99204.48041634  .00122310  00000-0  74510-3 0  9884
2 22878  35.1265 344.4899 0012714 296.0536  63.8885 15.75962106322207

The conjunction is sunlit and occurs close to the equator, south of
the Hawaiian Islands (roughly 1.3 S, 162 W) while Mir is on an
ascending node.  Unfortunately, the ground below is also sunlit,
so the conjunction won't be visible from the ground.

For those onboard Mir, if your feet point down toward the center
of the earth and you face into the "ram" direction (velocity vector),
the booster will come from the left and zip across to the right,
nearly perpendicular to Mir's flight path.  At this point it's too
close to call whether the booster will pass above or below Mir.
Using the above elements, the GPS rocket body passes just in front
of Mir by about 4 miles and ~100 meters above it.  If Mir arrives
just 1 second early (or conversely if the GPS R/B is 1 second late),
the Russians will be in for quite a scare.  --Rob