Fast algorithm for prediction of satellite imaging and communication opportunities

A new equation for nadir tracking estimation, taking into account secular p erturbations from the Earth's gravitational field and the influence of drag , is presented. The advantage of this proposed approach is that it needs to be solved just twice per day with respect to a specific ground target (the re are usually 14 orbital periods per day for sun synchronous orbit). The r esultant approximate near nadir angle time, whose root of mean square error is around a few seconds (i.e., similar to 30-km groundtrack error), is the n further refined using a newly developed controlling equation, reducing th e maximum error to about 0.4 s (similar to2.8 km groundtrack) for over 20 d ays prediction period. This is acceptable when the imaging field of view of 10 km is considered for high resolution small satellite cameras. The predi ction period of 60 days can be used for a typical small satellite camera wh ose field of view is about 100 km. This method can also be expanded to solv e the rise-and-set time problem. Because of the low complexity of the propo sed method, it is very suitable for implementation on the onboard processor whose computational resources are generally limited. The new computational process is described and simulation results are presented.