Orbit Determination Error Analysis System (ODEAS)

ODEAS is a general purpose, linear analysis system designed to evaluate the accuracy of the orbit determination process for various spacecraft. The basic orbit determination problem involves estimating values of a set of parameters based on an observation model. An estimated trajectory does not fit the measurements exactly due to inherent errors in the measurement process and imprecise knowledge of the dynamical process governing spacecraft propagation.

ODEAS incorporates both the batch and the sequential error analysis capabilities in a single system. The batch algorithm implements a weighted least square procedure. The sequential capability utilizes the Kalman filter algorithm. ODEAS simulates the data processing logic and computes the statistical characteristics of the orbit determination error on the basis of a prescribed tracking schedule and the expected accuracies of the orbital dynamics and measurement process.

ODEAS currently has measurement models for range, Doppler, and angle data for ground station tracking and TDRSS tracking, and some limited GPS tracking. ODEAS allows the following error sources to be considered, and some to be estimated, in the algorithm:

• Earth & planetary GM
• Earth & Moon non-spherical gravity models
• Planetary position errors
• Drag coefficient
• Solar flux error
• Solar reflectivity coefficient
• Measurement biases
• Station locations
• Station & onboard clock errors
• TDRS & GPS ephemeris errors
• Ionospheric & tropospheric refraction
• Impulsive & finite burn models

ODEAS has been used in the FDAB for over 10 years to assess orbital accuracy for a variety of low Earth, lunar, and libration point missions.