Prasun N. Desai Richard W. Powell NASA Langley Research Center Robert C. Blanchard

1. Entry Trajectory and Atmosphere Reconstruction Methodologies for the Mars Exploration Rover (MER) Mission Prasun N. Desai Richard W. Powell NASA Langley Research Center Robert C. Blanchard George Washington University October 8, 2003

2. Project Overview • Two Mars landers launched on June 10th (“Spirit”) and July 7th (“Opportunity”) of 2003 • Delivered to the surface using the Mars Pathfinder Entry, Descent and Landing system • Two rovers with 5 instruments to conduct remote and in-situ observations • Arrive January 4 and January 25, 2004 at two scientifically distinct sites • Operational life > 90 sols for each lander

3. MER Mission Animation

4. MER Entry, Descent, and Landing (EDL) Sequence

5. MER Lander Hardware

6. Reconstruction Approach • After landing of MER-A, reconstruction of entry is desired • Not only to assess the accuracy of the pre-entry predictions to the flight data, but to develop confidence in this prediction capability for the second landing of MER-B three weeks later • This understanding is crucial in order to have confidence in any changes that maybe proposed to assist the MER-B entry • MER reconstruction effort will closely follow approach employed for Mars Pathfinder (MPF) reconstruction • Multiple methodologies for flight reconstruction will be applied • Simple deterministic methods through statistical Kalman filter approaches • Reconstruct time and conditions of key events (e.g., parachute deployment, retro-rocket firing, etc.) • Reconstruct complete time history of position, velocity, and attitude • Reconstruct atmosphere and aerodynamics

7. Available Flight Data for Reconstruction • Two LN-200 Inertial Measurement Units will provide accelerometer and gyro data (one inside the backshell and one inside the rover) • Measurements will be sample at 8 Hz • During the parachute descent phase, altimeter data will be available from a first return RADAR • Antenna mounted at one of the lower corners of the lander tetrahedron • These data sets will only be available after landing

8. Deterministic Attitude Method • MER attitude reconstruction will follow approach utilized for Mars Pathfinder • MPF effort focused on reconstructing total angle-of-attack history to validate MPF aerodynamic database • MPF aerodynamics developed using only computational fluid dynamics (CFD) methods • CFD analysis predicted two bounded instabilities for the MPF conditions • Only accelerometer data available from MPF (no IMU flown) • Method utilized ratio of normal to axial forces and normal to axial aerodynamics coefficients to determine total angle-of-attack

9. Deterministic Attitude Method (cont’d) • The predicted value for the normal to axial ratio for MPF was calculated using the 6 DOF MPF simulation based on the POST code • Aerodynamic coefficients were obtained from the CFD analysis

10. Statistical Methods • Various “standard” statistical methods will be employed for MER reconstruction • Specifically, vehicle state history, and atmosphere and aerodynamic reconstruction • Effort will focus on using Sequential-Batch Least-Squares first • Advantage is allows processing short batches or segments of the data • Allows allows incorporation of navigation covariance errors and redundant data • After an initial “reference” trajectory is established, extended Kalman filter will be used • Focus will be to obtain an initial trajectory and atmosphere shortly after landing of MER-A • Further refinements will be performed after both landings

11. Summary • MER EDL reconstruction is required to develop confidence in pre-entry prediction capability • This effort is crucial since a second landing will occur three weeks later • Multiple reconstruction methodologies will be employed from simple deterministic to statistical Kalman filter approaches • MER reconstruction effort will closely follow approach employed for MPF reconstruction • Additional data sets will be available for MER as compared to MPF • Stay tuned on January 4th and January 25th …