RE: "bad" elset for #16194 (Met 3-1 r)

Ted Molczan (
Thu, 26 Dec 1996 20:28:32 -0500

Mike McCants:

>Ron Dantowitz said:
>>While tracking Met 3-1 r (#16194 / 85100  B) the satellite was "missing",
>>coordinates, but the satellite was TWELVE+ seconds late! (12.2 secs late).
>The problem is a "bad" elset.

We get them from time-to-time.

>This rocket has had a very slowing declining mean motion for
>a number of weeks  (Longitude resonance?). 

Yes, that's the cause. The object's orbit is almost 
exactly in 13th order resonance with the Earth's 
gravitational field. 

For the benefit of newcomers, resonance occurs when 
an orbit repeats the same groundtrack after a number 
of revolutions. In this case, the groundtrack (nearly)
repeats after every 13th revolution. This causes
normally small gravitational perturbations to continually 
build up into quite large orbital changes.

In the case of 85100B, the main effect is a long-term
periodic variation of the mean motion. Around 1986, the
period of variation was about 291 days, during which
the semi-major axis varied over a range of about 650
metres. I imagine that it behaves similarly today.

In his books Observing Earth Satellites (ISBN 0 333 33041 2), 
and A Tapestry of Orbits (ISBN 0 521 39323 X), Desmond 
King-Hele included discussions of his successful analysis of 
resonant orbit perturbations to accurately measure several 
of the Earth's tesseral (or longitudinal) gravitational 

Ted Molczan