WIND-TUNNEL TEST OF FLOW-THROUGH MARS PATHFINDER LANDER

The Pathfinder Lander, launched in December 1996, is scheduled to land on Mars July 4, 1997. The Lander is a tetrahedron with open edges and corners, permitting a moderate flow through the interior during parac hute descent. One of its scientific experiments is intended to measure ambient temperature and pressure during parachute descent by use of s ensors inside the Lander envelope. This location was required by safe landing considerations. Wind-tunnel and computational fluid dynamics s tudies were undertaken to determine whether valid atmospheric data cou ld be obtained by sensors so constrained, Internal flows through the w indow openings at the apex corners of the Lander were measured and com puted, Internal flow was found to be complex, recirculating, and highl y turbulent with velocities as small as 0.1 that of the freestream. Th e temperature sensor is in a region of fluctuating, negative (upstream ) velocity. This environment is clearly not optimum for atmospheric me asurements, and temperatures measured in parachute descent are likely to he thermally contaminated. The data reported here will be of value for evaluating the measurements and identifying requirements for meani ngful atmospheric measurements on future missions, They are also an in teresting example of secondary flow through a vented spacecraft.