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Orbit Determination at a Single Ground Station Using Range Rate Data 1 Daniel Coyle" and Henry J. Pernicka'' Abstract The solution of the spacecraft orbit determination problem is highly dependent upon the type of tracking data available at the ground station. Many algorithms exist for different types and combinations of tracking data. Well-funded tracking stations are typically able to supply six or more observed parameters simultaneously, enabling explicit solution of the orbit determination problem. The low-cost ground station under development at San Jose State University will initially be able to measure only Doppler shift as a function of time, thereby providing slant range rate as the single observable parameter. An algorithm enabling explicit solution of the orbit determination problem using range rate exclusively was not found, but orbit estimate improvement is still possible via differential correction. By utilizing a differential correction scheme in conjunction with a batch least squares estimator along with convergence improvements, the task of maintaining an acceptably accurate knowledge of the spacecraft orbit is made possible for a single ground station receiving a single measured parameter, even at higher levels of measurement noise and bias than those expected at the ground station.

Introduction The Spartnik microsatellite is currently being built and tested at San Jose State University (SJSU), with plans for its launch in the near future. The mission of the spacecraft is multifaceted, with an emphasis on the opportunity for students to take part in the design, fabrication, testing, launch, and operation of an actual spacecraft. The satellite will carry a particle impact detector and CCD camera, and will relay Earth imagery in the visible spectrum to the ground station at SJSU. 'Presented as paper AAS 00-120 at the AAS/AIAA Space Flight Mechanics Meeting, Clearwater, Florida, January 2000. 2Graduate Student, Department of Mechanical and Aerospace Engineering, San Jose State University, CA 95192-0087. 3 Associate Professor, Department of Mechanical and Aerospace Engineering, San Jose State University, CA 95192-0087. Currently; Associate Professor, Department of Mechanical and Aerospace Engineering and Engineering Mechanics, University of Missouri-Rolla, Rolla, MO 65409-0050. 327

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Necessary to the ability to track Spartnik is a capability to determine and maintain an accurate knowledge of the satellite orbit. At the program inception, a GPS unit was planned for use in orbit determination. The educational value of having the SJSU students perform the orbit determination themselves, however, was deemed to outweigh the advantages of an automated process. Consequently, the GPS unit will not be flown, and the orbit determination task will be performed at the ground station. The solution of the spacecraft orbit determination problem is highly dependent upon the type of tracking data available at the ground station. Many algorithms exist for different types and combinations of tr