On July 4, 1997, the Pathfinder spacecraft ushered in a new era of planetar
y exploration by successfully landing on the surface of Mars. The atmospher
ic entry and approach navigation activities required in support of this mis
sion are discussed. In particular, the flight software parameter update and
landing site prediction analyses performed by the Pathfinder operations na
vigation team are described. A suite of atmospheric entry simulation tools,
developed during Pathfinder's design cycle and utilized during flight oper
ations, is also presented. Data regarding the accuracy of the primary parac
hute deployment algorithm are extracted from the Pathfinder flight data, de
monstrating that this algorithm performed as predicted. The increased proba
bility of mission success through the software parameter update process is
discussed. The importance of modeling atmospheric flight uncertainties in t
he estimation of an accurate landing site is also demonstrated. With these
atmospheric effects included, the center of the final pre-entry landed elli
pse prediction differs from the postflight determined landing site by less
than 0.5 km in downrange and 5.0 km in crossrange.