Mars Exploration Rover

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LaRC

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

Mars Exploration Rover

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LaRCProject 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

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LaRCMER Mission Animation

Mars Exploration Rover

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LaRCMER Entry, Descent, and Landing (EDL)

Sequence

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LaRCMER Lander Hardware

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LaRCReconstruction 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

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LaRCAvailable 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

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LaRCDeterministic 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

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LaRCDeterministic 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

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LaRCStatistical 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

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LaRCSummary

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 …