SMART Orbit Determination by means of GPS Techniques: Accuracy and Simulation Results

SMART is a 50-kg multi-mission microsatellite hosting remote sensing payloads in sun-synchronous Low-Earth Orbits (400-1000 km). The engineering model of SMART, presented at the 48th IAF Congress (Oct. 1997, Turin, Italy), is being currently improved by the Depts. of Aerospace Engineering (2nd University of Naples, Italy) and of Space Science and Engineering “L. G. Napolitano” (University of Naples “Federico II”, Italy). A GPS Orbit and Attitude Measurement Subsystem (GOAMS) is planned for use as main source of state and attitude information. Knowledge of SMART state vector with GPS-based measurements and the related accuracy analysis are the topics developed in this paper. After outlining the mathematical background of least-squares estimation of carrier phase and pseudorange observables, the GOAMS parameters and performance are derived from software simulation of SMART dynamics. Results on phase and pseudorange observations show that the lower bound of obtainable accuracies, imposed by the GPS constellation geometry, is of the order of 0.2 m for the SMART position vector (with code-range measurements), 10^3 m/s and 10^-5 g for velocity and acceleration respectively (code-phase data). Good tracking accuracy, continuous tracking with reduced need of ground observations, together with consistent savings in cost, power and weight are the principal benefits gained by integration of GOAMS in SMART.