Orbital requirements for the Astronomical Roentgen Observatory Satellite

A preliminary examination was made of the orbital requirements for the satellite. The preferred orbit has a large eccentricity, a near-polar inclination, and perigee near the southern apex. The orbital stability is dominated by the very-long-term luni-solar perturbations which depend mainly on the orientation of the orbit with respect to the orbital planes of the disturbing bodies. There is no difficulty in satisfying the experimental requirements for a mission duration of one year. If a lifetime of four years is required, the launch time must be carefully selected or the orbit must be slightly modified. Short closures in the launch window can arise, possibly with a frequency of twice per lunar month.