Accurate Orbit Determination from Short-Arc Dense Observational Data

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Accurate Orbit Determination from Short-Arc Dense Observational Data1 David A. Vallado2 and Scott S. Carter'' Abstract Requirements have existed for several decades for highly accurate satellite orbits. With increased computer power, simplified analytical techniques have lost most of their competitive edge and numerical techniques are experiencing wide-spread popularity. When coupled with increased accuracy requirements from commercial satellites owners and accurate computations for debris and close approach for the International Space Station, a reliable method must be found to form highly-accurate satellite state vectors. This paper explores one approach using dense observational data from short-arcs of geographically distributed sensor sites. In particular, dense observations (consisting of one observation per second for about two minutes) are analyzed to determine the accuracy that can be achieved via high fidelity, numerical, orbit-determination techniques.

Introduction The basic processes for orbit determination are well-defined in the literature. With the widespread use of the modern computer, applications for precise orbit determination are now commonplace and increasingly, we perform them on the personal computer. This is coupled with a rapid growth in the use of space for satellite missions. An overview of orbit determination is presented in Fig. 1 [1]. From Fig. 1, we see that the accuracy of any orbit determination process ultimately relies on the observations and the computer processing of the data. We'll see later that quantity and quality of the observations are very important in this process. To evaluate the accuracy of an orbit determination method, we must use numerical techniques to preserve as much of the original accuracy of the observations. Thus for this paper, we will only consider differential correction (taking observational data and producing a state vector of position and velocity vectors) and propagation techniques (moving the satellite state vector through 1Presented at the AAS/AIAA Astrodynamics Specialist Conference, Sun Valley, Idaho, August 1997. 2Lt Col, USSPACECom/AN, 250 S. Peterson Blvd. Suite 116 Peterson AFB, CO. 80914-3180. email: [email protected]. 3Capt, Air Force Research Laboratory, 3550 Aberdeen Ave, SE, Kirtland AFB, NM, 87117-5776. email: [email protected].


Vallado and Carter


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FIG. 1. Representation of Orbit Determination. Many Mission Application s, shown at the Lower Right, require Observations, Orbital Element Sets, and Ephemeride s. Future Observations Complete the Cycle.

time) that use robust numerical techniques. The use of simplified analytical techniques is inconsistent with a goal of exploring accurate orbits. Although there are numerous high-fidelity numerical programs, we used the operational version of Goddard Trajectory Determination System (GTDS) from NASNGoddard to perform most of the analyses and appreciate the support of Joseph Toth. We are also grateful to Paul Cefola for the use of the Draper Laboratory Res