Given the constant orbit, the only guidance, navigation, and control (GNC) to be performed is maintenance of the orbit. The orbit will degrade over time due to perturbations, making stationkeeping necessary. The fuel mass necessary for stationkeeping is dealt with in the “Stationkeeping” section. However, the control aspect itself is dealt with separately in this section. The primary tradeoff for the GNC subsystem, in this case, is whether to perform orbit control autonomously or via ground station. As there are no issues with satellite to ground station communication, performing orbit control via ground station is the best choice. Though autonomous control would result in a more robust system, the infrequent need for stationkeeping maneuvers makes it unlikely that any issues with ground station control would result in mission degradation or failure.
The orbit determination requires three main elements – collection of data, algorithms for orbit modeling, and software to process the observations. The algorithms and software used are often commercial packages, or if they are custom implementations, are based off well established methods. However, the data collection can be performed in multiple different ways. Given that a star tracker is necessary for ADACs, though, the issue of collecting data about the orbit is already solved. A star tracker will be used to collect the necessary information for orbit determination. An additional benefit of using the star tracker, aside from the fact that it is already in use for a different subsystem, is the high accuracy it can provide (higher than needed for this mission’s orbit determination, in fact).
