Geosynchronous satellites at sub-synchronous altitudes

This paper looks into the possibility of achieving geosynchronous satellite behavior at sub-synchronous altitudes. A constant external centrifugal force is needed to achieve this objective. The force is of the order of 15 N/ton of satellite mass per 1000 km of lowering of the geostationary altitude. Finally, the paper analyses the two-body and multi-body tethered systems to explore the possibility of geostationary configurations wherein the "balancing force" develops internally as tether tension.