Satgen84  HOW HIGH IS MIR     DOVE MANUAL      by GM4IHJ 5th Nov 90

Low altitude Space stations like the Russian MIR, are awkward beasts to
track, even if you have a smart computer and, lots of up to date Keplerian
elements. The problem arises because atmospheric drag rapidly reduces
Mir's height, requiring that it use its engines to alter its orbit at
frequent intervals. Orbit height changes of 30 or 40 kms are frequent and
worse still are not officially reported. NASA rarely catch up with them
until a week or so later, by which time , Mir's orbit timings and your
computer predictions can differ by 16 minutes per day times 7 days.

Mir's tracking rules predict Mir passing UK 5 times per day with about 96
minutes between each pass. An orbit one day can be followed the next day
by an orbit timed between 14 and 40 minutes later, depending on Mir's
orbital height.

In fact if we know how many minutes later Mir is per day , we can work out
its height and its orbit period. Table 1 below works it out for us :-

PERIOD   MEAN HEIGHT   MINS LATER PER DAY        REMARKS
90.9       323km           14.4            Rarely below this height
91.1       333             17.6    
91.3       343             20.8
91.5       353             24.0         Usual height for Soyuz crew change
91.7       363             27.2
91.9       373             30.4         Regular cruising height
92.1       383             33.6
92.3       393             36.8
92.5       403             40.0         Recent highest height
92.7       413             43.2

Note the time you hear Mir each day. This last week has been 26/0632 and
0804: 27/0709 and 0845: 28/0613 and 0749: 29/0652 : and 31st/0636 and 0813
Shifts of 37, 41, 40, 39, and 40.5 (2day gap 81 minutes). So Mir is near
the top of its flight envelope and can be expected to drag down slowly
with minutes later per day getting noticably less each week.

Mir is presently coming over UK when the Cosmonauts are asleep . So do not
expect to hear them again until perhaps Nov 10th or later when their orbit
past UK (across SE sky), around 2000 ut should be audible on 143.625 FM.

The Dove Manual is now avaible. SASE to 8 Whitehills Saline Fife KY12 9UJ
will get you details. 73 de John GM4IHJ @ GB7SAN  5th Nov 90