Navigation flight operations for Mars Pathfinder

A detailed description of the techniques used and results obtained for the interplanetary navigation of the Mars Pathfinder spacecraft is presented. M ars Pathfinder was launched on Dec. 4, 1996, and landed on Mars on July 4, 1997. To ensure a successful landing, the navigation team was required to g uide the vehicle such that the flight-path angle error was less than 1.0 de g at atmospheric entry. This relatively tight requirement was achieved thro ugh the use of a ground-based orbit determination system ming Doppler and r ange measurements obtained from Earth stations. The resulting orbit solutio ns were used to design and execute four trajectory correction maneuvers nee ded to ensure the vehicle would make a correct atmospheric entry. More freq uent orbit solutions were performed during the final two days to predict th e exact time of entry and preset the onboard entry, descent, and landing se quence to deploy the parachute at the correct moment. The overall result wa s a successful landing less than 30 km from the intended target, well withi n the 100 x 200 km requirement ellipse.