Re: 80-008B tumbling? plus a couple of other items

Alan Pickup (alan@wingar.demon.co.uk)
Sat, 22 Mar 1997 12:06:42 +0000 

In message <9703221039.AA25724@cds.plasma.mpe-garching.mpg.de>, Bjoern
Gimle <b_gimle@algonet.se> writes
>Ed Cannon <ecannon@mail.utexas.edu> wrote:
>>
>>Just wondering -- How much longer will Cosmos 2053 (20389, 89-100A)
stay in
>>orbit?
>> (elsets clipped)
>With these elsets, SatEvo gives 1997 Aug.22,25,31,31 and Sep.9 as decay
>prediction, reflecting the decreasing ndot2 values.
>

The 109 elsets I have for this object since the beginning of 1997 show a
spread of decay date between July 13 and (1998) January 6 using SatEvo.
Recent elsets average to a decay around late-August.

>For a near-circular orbit like this, you can estimate the remaining
>lifetime as Q/ndot2,  where Q is about 0.10 days (actually days^-1,
>since ndot2 is in orbits/day^2). This leads to a much longer lifetime
>than SatEvo, which puzzles me.
>
>Q decreases at higher MM. For elliptic orbits, Q is much higher,
>but seldom more than 2*(16.6-MM)

Using King-Hele's definitions, Lifetime = Q/ndot

Elsets give you ndot2 which is half ndot, so Lifetime = Q/(2*ndot2)

Q is about about 0.1 rev/day for a circular orbit at 16.2 revs/day MM
(mean motion). However, at 15.8 revs/day (as per this object) it is
closer to 0.14 (using King-Hele's graphs).

Taking ndot2 = 0.00044 and Q = 0.14 about day 97080:

        Lifetime = 0.14 / (2 * 0.00044) days

                 = 159 days

        Decay date = 97080 + 159

                   = 97239

                   = 1997 August 27

                   = not a million years from the SatEvo prediction :-)

ref: 

1. Desmond King-Hele "Methods for Predicting Satellite Orbital
     Lifetimes" (Royal Aircraft Establishment, Tech Report 77111,
     July 1977)
2. Desmond King-Hele "The Prediction of Satellite Lifetimes"
     (RAE, Tech Report 87030, May 1987)
3. Desmond King-Hele book "Satellite Orbits in an Atmosphere"
     (Blackie, 1987)

Alan
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