As there is no appreciable atmosphere on the Moon, satellites can orbit at any chosen altitude down to the altitude of the highest mountains. Mass anomalies can cause perturbations in the orbit and these should be known. A possible solution could be the Lunar equivalent of the terrestrial MLAT system used by aviation comprising a number of ground receivers triangulating satellites as they pass over. A certain amount of control using thrusters would be useful to control the configuration of the constellation. Primary missions could be surveillance of both the bright and dark sides using radar, radio reception and magnetometers. These data as well as the orbit parameters (Keplerian Co-ordinates) would need to be monitored by ground stations making this a large wide ranging project.