93-164
In-Situ Radio-Metric Tracking To Support Navigation For Interplanetary Missions With Multiple Spacecraft
Robert D. Kahn*, Sam W. Thurman** and Charles D. Edwards***
Abstract
Doppler and ranging measurements between spacecraft can be obtained only when the ratio of the total received signal power to noise power density (Pt/No) at the receiving spacecraft is sufficiently large that reliable signal detection can be achieved within a reasonable time period. In this paper, the requirement on Pt/No for reliable carrier signal detection is calculated as a function of various system parameters, including characteristics of the spacecraft computing hardware and a priori uncertainty in spacecraft-spacecraft relative velocity and acceleration. Also calculated is the Pt/No requirement for reliable detection of a ranging signal, consisting of a carrier with pseudo-noise phase modulation. Once the Pt/No requirement is determined, then for a given set of assumed spacecraft telecommunication characteristics (transmitted signal power, antenna gains, receiver noise temperatures) it is possible to calculate the maximum range at which a carrier signal or ranging signal may be acquired. For example, if a Mars lander and a spacecraft approaching Mars are each equipped with 1-meter diameter antennas, the transmitted power is 5 Watts, and the receiver noise temperatures are 350 K, then S-Band carrier signal acquisition can be achieved at ranges exceeding 10 million kilometers.
A brief error covariance analysis has been conducted to illustrate the utility of in situ Doppler and ranging measurements for Mars approach navigation. The results indicate that navigation accuracies of a few kilometers can be achieved with either data type. The analysis also illustrates dependency of the achievable accuracy on the approach trajectory velocity
* Member of the Technical Staff, Tracking Systems and Applications Section, Jet Propulsion Laboratory, California Institute of Technology, MS 238-600. 4800 Oak Grove Drive, Pasadena, California 91109.
** Member of the Technical Staff, Navigation Systems Section, Jet Propulsion Laboratory, California Institute of Technology MS301-125J, 4800 Oak Grove Drive, Pasadena, California 91109. Member AAS.
*** Technical Group Supervisor, Tracking Systems and Applications Section, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109.