LOOPUS (Loops in Orbit Occupied by Unstationary Satellite) Orbit

The Loopus (Loops in Orbit Occupied by Unstationary Satellite) orbit is a proposed ¹ for a communication system based on a constellation of satellites in inclined, highly elliptical orbits. In such orbits, satellites appear quasi-stationary for several hours around apogee and are visible at very high elevations, making the concept particularly attractive for user terminals at high northern latitudes.

A representative LOOPUS system comprises nine satellites arranged in three highly inclined (63.4°) highly elliptical orbits, with three satellites in each orbit. Each orbit has a period of approximately 14.4 hours, with satellites spaced 120° apart in argument of latitude. The nominal apogee altitude is about 41,450 km and the perigee altitude about 5,784 km, enabling continuous 24-hour coverage of selected regions in the Northern Hemisphere.

The relative motion of the satellites with respect to the Earth produces two cross-over points in the ground track of the subsatellite points. Each satellite requires approximately 8 hours of its 14.4-hour orbit to travel from one cross-over point, through apogee, and back to the same cross-over point. From the perspective of a ground terminal, the nine satellites appear to follow one another along essentially the same ground track, with successive satellites becoming visible in turn. After approximately 71 hours and 46 minutes, the first satellite in the sequence becomes visible again. With appropriate selection of the orbital parameters, handover between descending and ascending satellites at the cross-over points can be managed by a single Earth station.