Satgen 460  Visual Misconceptions   by GM4IHJ  (BID SGEN460)  17Jan98

Any one familiar with visual tracking of satellites probably uses Mir
or the Space Shuttle as the big obvious targets, with the numerous
smaller Transit Navigation satellites as a secondary alternative, for
showing youngsters just how much is going on , over their heads.

Talk to school children , and if they have ever seen any of these big
targets, they generally have the view that they have seen them because
they carry " bright lights". Few if any casual observers are aware
that these vehicles have no bright lights , but simply function as
very effective reflectors of sunlight. Sunlight they can see from
their high altitude, whilst the earth beneath them is in pre dawn or
post sunset darkness.

Now and again some publications ( Eg Sky and Telescope), give details
of other attractive visual targets, such as UARS a satellite
monitoring the Upper Atmosphere. More recently however a lot of new
targets have appeared in the Iridium mobile phone constellation. The
problem is that many radio amateurs seem to equate mobile phone
satellites with Amsats minisat store and forward data birds, assuming
incorrectly that the Iridium series are tiny minisat cubes. When in
fact they are very big satellites indeed, with a typical Iridium sat
having two solar panel each of which is a monster shiny reflecting
surface approximately 6 x 2 metres in length and width. 

So what we have now is 45, ( soon to be 66 ) satellites in low earth
orbits at 700 kms altitude following 86 degree inclination orbits with
11 satellites in each orbit plane. Which works out at one satellite
passing every 10 minutes , and as one dissappears another comes in
view very shortly . They see the Sun from about 150 minutes before
dawn until 50 minutes before dawn , and from 50 minutes to about 150
minutes after sunset . They follow simple paths whereby on a clear
starry night, a Northern hemisphere Temperate Latitude station sees
them going south to north across his eastern sky and, going north to
south across his western sky. Southern hemisphere Temperate Latitude
stations see north to south movement across their eastern sky and,
south to north across their western sky. 

At the moment some of these big birds appear to be slowly flashing as
their solar panels turn in and out of sunlight. So do not be surprised
if they go from faint to very bright quite quickly , but not quickly
enough to be mistaken for quick flashing aircraft lights which may
also have a tell tale colour . The light from the satellights is plain
reflected sunlight.

You can get Iridium satellite keplerian elements from :-
http://www.grove.net/~tkelso/NORAD/elements/tle-new.txt

PS.  ESA have stated that Ariane 503 will be a "QUALIFICATION" flight.
ie not a commercial flight, and it will probably launch in June 98.
The first 500 series commercial launch is not expected until the end
of 1998.