Hi Bob and Nico,

I want to add some info about this problem.

If You have the ARRL Satellite Handbook, see  page A-8 (Appendix A - Satellite Orbits).

There is Equation 13a, which give us the value - rate of change of argument of perigee in degrees per day.

The value for RS-44 with  current TLE data is   -2.3331333 degrees per day.

A negative value means that the ARGP angle will be smaller tomorrow.

For example 180  degrees divided by -2.3331333 is approx. -77.1495471 days.

So, in 77.15 days the positions of the apogee and perigee will be swaped. And yet, if we have apogee in the best position for some rare qso with RS-44 transponder,  this situation will be repeated 2.366 times per year.

My calculation: 360/2.3331333 = 154.2989 and 365 days / 154.2989 is 2.366

With the same equation 13a  we can calculate the famous angle of 63.435 degrees of inclination with zero drift as Nico says. This angle was used by the old Russian Molnia satellites at a time when it was still difficult to reach a geostationary orbit.

My favorite FO-29 (now probably nice history) has Rate of change ARGP -2.573348 deg/day. Yet, AO-91 with elliptical orbit (apogee 811.8 km /perigee 453.6 km) has Rate of change ARGP  = -3.251476 degrees/day, so it takes -55.359 days for exchange apogee and perigee positions..

It is very good to check the ARGP angle in the TLE data when working via elliptical orbiting satellites. For example, for the qso between the eastern costs of the USA and Europe, we need an orbit height of approximately 950 km (for OK stations). FO-29has an apogee height of 1320.8 km, perigee 801.2 km. It was not possible to make with the apogee in the wrong position QSO  USA-Europe...

73 Jarda ok2gz