Re: Molniya 3-11 decay

Chris Peat (
Tue, 15 Sep 1998 12:21:52 +0200

Tony Beresford wrote (in answer to Jay Respler);

>>Do Molniya keep their special orbit by rocket firings during their
>>lifetime, or are natural forces enough to hold them ?
>I dont know the answer to that question Jay. However it
>is appropiate to point out that the lunar/solar pertubations that
>effect the perigee height are conservative forces, and the dont affect
>the orbital energy and hence the period or semi-major axis.
>So thruster firings to maintain the 12 hour sidereal period
>of the object is not required.

The important point about Molniya orbits is there inclination of 63.4
degrees which
is precisely the value needed to stop the argument of perigee precessing due
to the
earth's flattening. At all other inclinations, the perigee and apogee will
rotate within the orbital
plane over time, thus the apogee would not remain over the northern (or
southern) hemisphere
as desired. The value of this critical inclination doesn't depend upon the
semi-major axis, and
so is relatively immune to the lunar/solar perturbations.


Chris Peat, Anite Systems
Currently working at the German Space Operations Centre near Munich