Recovering Time and State for Small Satellites in Deep Space

Autonomous navigation in the satellite world is at best, a semi-autonomous solution. All systems currently require an outside presence or prior state to get a navigation. As the small satellite revolution brings about numerous more spacecraft, the need for truly autonomous navigation becomes a greater necessity for deep space travel as communication resources become limited. When spacecraft are in deep space, communication times between a satellite and the Earth can be prohibitive and ride-sharing opportunities as well as on-board faults can leave the spacecraft without time information. The proposed approach uses optical observations of available planets and corresponding celestial satellites (for interplanetary operations) to initially recover the approximate time and state. These observations are then followed by precise, filter-based determination of time, position and velocity from the chosen optical beacons available in interplanetary spaceflight. The innovation of this approach is to use the periodicity of celestial bodies and artificial satellites to initially determine time. This capability is analogous to that of advanced star trackers that can initialize themselves by identifying any star field in the celestial sphere. Being able to quickly and autonomously recover time and position from an environment with no Earth contact will advance mission safety and automation from current methods which require an Earth contact. The impact of this concept crosses both human (full loss of communication scenario) and robotic (autonomous recovery from onboard fault) exploration applications, where some form of spacecraft-to-ground communication is required to establish approximates for time and position. In both cases, the current state-of-the-art navigation systems require some knowledge of time and some approximate position to initialize the estimation process before the mission objectives can be obtained. This presentation will examine the best-known solution for time in different scenarios related to the future of small satellite missions. While the solution is applicable to a wide range of missions, small satellites used for solar system exploration will be the focus as small satellite solutions can then be scaled to larger spacecraft