Far field approximation for a nozzle exhausting into a vacuum.

a perfect update of velocity, position, and attitude occurs prior to the burn from the parking orbit. The system parameters used in the evaluation technique can be estimated using techniques that are relatively unsophisticated but are of sufficient accuracy to accomplish the desired result. These techniques were implemented in computer programs now in use at NASA/ERG. The computer programs were exercised on a Jupiter flyby mission. For this mission and the assumptions made, it can be concluded that the accuracy of the strapdown guidance systems evaluated is adequate to accomplish the guidance and navigation of a Jupiter flyby mission. If the first midcourse correction is made 10 days after launch and the required probability of mission failure attributable to guidance is 0.05, the reliability (mean time to failure) of the pure inertial strapdown guidance systems considered is such that no system examined would succeed if operated continuously from launch to midcourse. If the probability of mission failure attributable to guidance is relaxed to 0.1, the two specified systems still fail if midcourse correction is made 10 days after launch. An optimum system which will succeed is found. Concentrated attention to reduction of system power requirements would yield a significant reduction in the weight attributable to guidance for this specific mission. This might be achieved by development of a lightweight variable thermal impedance for the ISU.