In-orbit VELOX-II orbit propagator performance study using pre-processed two-line-element method

Abstract

Due to the limitation of microcontroller which has a seven significant digit of floating point input, it results in a loss of 30 to 60 seconds of time epoch information if used in satellite’s orbit propagator. This leads to an orbit propagation error of 200 km observed in the initial flight data of VELOX-PII picosatellite’s attitude determination and control system (ADCS). This error can be corrected by using a pre-processed method. In our new VELOX-II nanosatellite mission, both the primary and secondary payloads require a pointing accuracy better than 5 degrees. High orbit propagation error results in a higher attitude determination error. To improve the orbit propagation accuracy without either occupying additional microcontroller memory or physical space in the VELOX-II, a pre-process two-line element method was proposed. Initial theoretical study has shown that the orbit propagation accuracy of 20 km error and target pointing knowledge error less than 1 degree can be achieved. In this paper, the in-orbit data of VELOX-II is compared with real-time GPS data and ground propagated data to verify the accuracy of the proposed preprocessed TLE method. In addition, the pointing accuracy of VELOX-II is studied based on the sun sensor and magnetometer data obtained from in-orbit flight data.