Solar TDOA measurement and integrated navigation for formation flying

To improve the positioning accuracy of autonomous celestial navigation systems when flying in formation, we exploit the fact that the sole light source in the solar system is the Sun to directly provide positioning information for relative navigation. We term this solar Time Difference of Arrival (TDOA) navigation for formation flying. Solar light has the potential to provide a solar Time of Arrival (TOA) because of its unstable intensity. However, the solar TOA cannot be used for navigation because it has no baseline. To solve this problem, we took the difference between the solar TOAs of two spacecraft (the solar TDOA) as the basis for navigational measurement. The solar TDOA represents the relative distance between two spacecraft in a radial direction. However, whilst the solar TDOA is insensitive to solar direction errors, a free-standing solar TDOA navigation system is not observable. We therefore combined the solar TDOA with the Mars direction and inter-satellite link navigation system, to form an integrated solar TDOA/Mars direction/inter-satellite link navigation method for formation flying. Simulation results indicate that solar TDOA-based integrated navigation for formation flying can provide highly accurate navigation information, especially under relative conditions.