ABSTRACT
As seen in Chapter 6, to determine the spacecraft attitude, one needs to know a set of observed (measured) astronomical vectors and the corresponding ephemeris astronomical vectors at the given time. This chapter provides the information on how to measure the astronomical vectors and calculate the corresponding ephemeris astronomical vectors at any given time. Several most widely used astronomical vectors are considered. Section 7.1 discusses the star trackers, which use star catalogs to get ephemeris star information and charge coupled device (CCD) to measure the vector the instrument is pointing to. Using this information, methods discussed in Chapter 6 can be used to determine the spacecraft attitude. Section 7.2 is focused on Earth’s magnet field vector, which includes the mathematical formulas to calculate ephemeris Earth’s magnet field vector and measurement for Earth’s magnet field vector. Section 7.3 provides the formula to calculate ephemeris Sun vector and a measurement method for getting the Sun vector.
