Satgen 618  ISS and MIR   by GM4IHJ   (BID SGEN618)   2001-01-27

Today 24th January 2001, the international space station is a morning
object over Scotland. None the less, several observers have reported
it as a very bright object in the evening sky for the past week. The
fact that what they are reporting is the planet Venus - an almost
stationary target in the sky, rather than a fast moving satellite, is
a consequence of their being misled by the press. Noting that
newspaper reporters who have never bothered to look for ISS. Insist
on describing it as a "magnificent bright object". 

Unfortunately ISS is not yet all that bright. The recent addition of
big solar panels, has not added much to its ability to reflect
sunlight to earth. So it actually disappointed many viewers who saw
it when it was an evening object here in the North, about a month
ago.

ISS follows a roughly 60 day cycle. Appearing as a sunlit object
passing across your starlit post sunset sky for a few nights in
succession , roughly every 2 months. It is not much brighter than the
much older MIR station ,now in its last few weeks in orbit. Hopefully
however, ISS will get a lot brighter as more bits are added over the
next months and years.

Stations located in the northern hemisphere above latitude 40N , all
see ISS at roughly the same local time . ie an 1830 local London pass
will be followed much later by an approximately 1830 local time pass
in Calgary Alberta. Both will get 5 or 6 successive orbits a day but
not all orbits will be sunlit post sunset. Equatorial stations have a
different pattern of orbit passes in a given day. They get perhaps 2
passes then a break of about 11 hours occurs before they get 2 more
passes. While stations much further south in the southern hemisphere
get a 4 to 6 consecutive orbit pattern very similar to that at
stations above 40N, but at a different local timing from that of the
northern stations.

Meanwhile MIR is still up there and it is as good a post sunset
visual target as ISS. Interestingly enough in the 4th week of
February MIR will nearly be in the same part of the sky as ISS,
provided its orbit is not greatly changed by then. Unfortunately , it
appears presently, that one will be in the eastern sky whilst the
other is in the western sky. So unless MIRs orbit shifts dramatically
we are unlikely to see the two stations flying in formation. Pity
really. We have not had stations flying in orbit since Salyut 7 and
Soyuz did it 15 years ago. MIRs funeral date has recently been put
back until March 6th. Even this date is provisional . It being more
important to get the re entry conditions exactly right, than to do it
on a particular day. As its altitude is reduced from 320 to about 160
kms , it will become an even better visual object . Although
forecasting its actual pass times as its orbital elements change ,
will be difficult . Though the old (pre computer) rule, X minutes
early today, 2X minutes early tomorrow , may help. But what ever
happens, the Russians have done a great job. So many voice and packet
QSOs. Grateful thanks to all who kept MIR flying. MIR will be missed.