A Pre-Processed Orbital Parameters Approach for Improving Cubesat Orbit Propagator and Attitude Determination

Abstract

Nanyang Technological University has built and successfully launched the VELOX-PII and VELOX-I cubesats. Both of the satellites carry a low-power consumption in-house-developed attitude determination and control subsystem (ADCS). The ADCS uses an 8-bit microcontroller. However, in-orbit propagation data indicates that the ADCS suffers high orbit propagation error due to the finite word length of the processor. High orbit propagation error could lead to a higher attitude determination error that affects the satellite's pointing accuracy. This paper presents a pre-processed orbit parameter method to minimize the orbit propagation and attitude determination errors. The two-line-element (TLE) data is propagated to the nearest seven significant digits of a selected time epoch. The time epoch selection is required to fulfill the single precision floating point conversion constraint. The orbit propagator performance has been evaluated for modified orbital parameters in both Geocentric Celestial and true equator mean equinox reference frames, direct input of NORAD TLE, and SGP4 methods using the VELOX-I and FORMOSAT-3/Cosmic Global Positioning System data. The results show a reduction in propagation error on the order of one to two magnitudes. In addition, the method proposed has the lowest attitude determination and target pointing error when compared with different TLE input methods.