This paper presents accurate orbit determination (OD) of the Iran University of Science and Technology Satellite (IUSTSAT) from Global Positioning System (GPS) data. The GPS position data are treated as pseudo-measurements within an onboard orbit determination process that is based on the numerical integration of the equations of motion using an earth gravity model and applying an Extended Kalman Filter for the data processing. In this paper, through accurate tuning of GPS duty cycle and on/off time intervals, a solution is suggested to achieve the desired OD accuracy despite power constraints. Moreover, a new scheme for automatic fault management in the orbit determination system is derived that provides fault detection and accommodation features. K E Y WO R D S 1. Orbit determination. 2. GPS. 3. Kalman filter. 4. Fault detection and accommodation.
In this paper, gradient method is applied to the problem of satellite orbit determination. We used the ground station data (range, azimuth and elevation), for calculating the satellite position vector in the ECI frame. Satellite orbit is in the elliptic shape and satellite turns in orbital plane. Hence, orbit frame (PQW) is defined. Based on representation of input data in the PQW frame, we can define an ellipse. With the characteristics of an ellipse, beside definition of cost function and optimization technique, the satellite orbit is determined. This method, which can be easily implemented in hardware with moderate computational complexity, yield an efficient satellite positioning without assuming a prior knowledge of measurement noise. The performance, accuracy and error of algorithm are checked, by a test case.
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