Analytic approach for near circular orbit determination

Future missions including satellite constellations, formation flying and precise target pointing will require accurate and up-to-date orbital knowledge, especially frequent orbit maintenance manoeuvring is involved. Autonomous onboard orbit determination can be preferred in order to minimise the costly ground segment. Recently low cost and low power GPS (Global Positioning System) receivers are also available as an orbit sensor, which enable us to implement the onboard orbit determination function on micro or even nano satellites. The heavy computational demand required for executing orbit determination, however, is not desirable for the onboard processing environment. In this paper, we describe our approach to design the orbit estimator by using our analytic modelling of perturbed orbit for near circular low earth orbits, called epicyclic orbit. To use the analytic orbit for the estimator extensively reduces the computational demands because no numerical integrator is required to propagate the orbit and the variational equation of orbit. We present the way we have implemented the orbit estimator based upon the epicycle description of perturbed orbit. Some simulation results and UoSat-12 orbit processed by onboard GPS measurements are also shown.