A star tracker design for CubeSats

This paper outlines a low-cost, low-power, arc-minute accurate star tracker that is designed for use on a CubeSat. The device is being developed at the University of Texas at Austin for use on two different 3-unit CubeSat missions. The hardware consists of commercial off-the-shelf parts designed for use in industrial machine vision systems and employs a 1024×768 grey-scale charge coupled device (CCD) sensor. The software includes the three standard steps in star tracking: centroiding, star identification, and attitude determination. Centroiding algorithms were developed in-house. The star identification code was adapted from the Pyramid Star Identification technique developed by Mortari. Attitude determination was performed using Markley´s singular value decomposition method. The star tracker was then tested with both internal and external simulated star-fields and night-sky tests. The resulting accuracy was on the order of arc-minutes. It was concluded that this system is a viable option for CubeSats looking to improve their attitude determination. Further proof of the system will be obtained when the star tracker flies on the planned CubeSat missions in 2013 or later.