Re: Granat to reenter next year

Jason Hatton (jason.hatton@etss.u-strasbg.fr)
Thu, 12 Nov 1998 09:31:50 +0000

Björn Gimle wrote:

> The Mean Motion is still 0.24, so it will appear nearly at the same time
> every four days. The perigee is at 15N, near sunset, so when and if there
> is a perigee pass near the time of your local sunset, you may have a chance
> of seeing it at a range of 6000 to 9000 km from the northern hemisphere.
> Predicted magnitude 10-11, even at my latitude, because of the improving
> phase angle. My best chance should be Nov.30, western USA's Dec.12, but
> conditions may repeat throughout winter.

I made one unsuccessful attempt to observe Granat some months ago at a
predicted range of 10000km. However, the main problem in observing
Granat & other satellites in similar orbits (such as Astron) is that the
SGP4 prediction routine used by most prediction software may not be
accurate enough due to the strong solar / lunar perturbations near
apogee. I compared consecutive elsets for Granat & found that the
predicted position often varied by at least an  hour between elsets. So
in order to make useful predictions it is very important to use elsets
taken near perigee which we made on the same orbit as the intended
observation. Unfortunately, it seems that elements for Granat are
updated only irregularly (at best once per orbit = 4 days, at worst
every 3rd or 4th orbit). Does anybody know of any software packages
which can accurately predict the position of a satellite in a highly
eccentric orbit which is subject to significant solar / lunar
pertubations?     


Best wishes & clear skies,

Jason

-- 
Dr Jason P Hatton
INSERM U311
ETS Strasbourg
B.P. 36
10 Rue Spielmann
67065 Strasbourg Cedex
France

48.538N / 7.731E / 143m