Satgen361  Goodbye Jianbing ?        by GM4IHJ                   24 Feb 96

Several correspondents ask . "How can we follow the soon to self destruct
Chinese satellite" ? The answer is "not easily". The prediction of where a
run away satellite will come to earth is more art/guess than science. But
as Jianbing is unlikely to be the last to meet this fate ( our own Oscar
13 is probably the next kamikaze ), it may be useful to record just what
is happening to Jianbing at the various stages of its uncontrolled
descent.

The data needed is simple to obtain , if you have access to the Keplerian 
elements (object 22870U 93063H), which are appearing every 3 or 4 days
here on amateur packet radio bulletin boards. The table below lists data
recovered from study of these Jianbing Keplerian elements. Period ,
Perigee and Apogee are calculated in the following simple basic programme
:-
10 Input "mean Motion" ;MM
20 Input "eccentricity";ECC
30 LET T=1440/MM          :REM get period in minutes
40 LET A=331.25*T^(2/3)   : Gets length of the orbit major axis
50 LET APOGEE=A*(1+ECC)-6378    
60 LET PERIGEE=A*(1-ECC)-6378
70 PRINT "Period = ";T;"  Apogee = ";APOGEE;"   Perigee = ";PERIGEE

The Table below shows how these orbit features have changed since 1993

Jianbing data file
Date    21Oct93 1Dec95  1Feb96   5Feb96   13Feb96  16Feb96  21Feb96

Period   118.22   96.35   93.744   93.466   92.814   92.487  91.92 mins

Perigee   179     163     155      153      152      151     149 kms

Apogee   3024    1004     760      735      672      641     588 kms

Perigee Latitude  40 S    1 S      2 N      15 N     21 N    29 N

Apogee decline         4       6        8         10      10.6 kms/day

Period decline       .04     .07       .08       .109    .11 min/day

Perigee Latitude is obtained by computing from the Kep Elements using
ordinary tracking software. Apogee and perigee decline are averaged
changes in these factors between their respective dates. If the Apogee
data is graph plotted against date, the curve descends below 150 kms at
around 9th to 11th March 96. Graph plotting the decline in period produces
a curve which goes below 89 minutes period on about 9th March. But both
these curves may steepen still further producing a slightly earlier crash
date. Nothing is certain but Keplerian elements published this next week
should allow a clearer forecast.

Oscar 13 has a much smaller mass , and a different shape which suggests
its final decay curve may be steeper than Jianbings