Early orbit methods
Abstract
The estimator algorithm in the Goddard Trajectory Determination System (GTDS) requires an a priori estimate of the spacecraft position and velocity in order to initiate the iterative estimation process. GTDS has been provided with the capability to determine a starting value of position and velocity from a limited number of discrete tracking data samples. Three techniques are optionally provided to perform this function. They are as follows: The Gauss method and double riteration method. These deterministic methods use three sets of chronologically ordered gimbal angle observation pairs to solve for the six Cartesian position and velocity components at an epoch time equal to that of the second observation: and the range and angles method. This method uses multiple (more than two) sets of simultaneously measured range and gimbal angle data from the GRARR, ATSR, USB or CBand radar systems. Two body equations are regressively fitted to the transformed data to yield epoch values of the spacecraft position and velocity.
 Publication:

In its Mathematical Theory of the Goddard Trajectory Determination System 31 p (SEE N7624291 1513
 Pub Date:
 April 1976
 Bibcode:
 1976mtdt.reptW.....
 Keywords:

 Orbital Position Estimation;
 Orbital Velocity;
 Spacecraft Trajectories;
 Trajectory Optimization;
 Algorithms;
 Iterative Solution;
 Radar Tracking;
 Time Measurement;
 Astrodynamics