Position uncertainty during autonomous manoeuvres such as orbit-raising/de-orbiting requires that the local knowledge during low thrust (i.e. with electric propulsion) is accurately determined.
Current orbit-raising assumes semi-autonomous control assisted by GNSS, with a long time integral to measure increasing altitude and trajectory of the satellite.
The use of a hybrid GNSS unit that incorporates a low power INS (Inertial Navigation System) and potentially other sensor capabilities (e.g. millimetre wave radar/lidar, stereo cameras) provides a mechanism through which control can be fully or highly autonomous for close manoeuvre in combination with methodologies for modulating electric thrusters.
The understanding of spacecraft position, orientation and velocity gradient with a capable hybrid GNSS unit may provide further mission management opportunities to maximise propellant utilisation.