SIMULATED RAREFIED AERODYNAMICS OF THE MAGELLAN SPACECRAFT DURING AEROBRAKING

Aerodynamic loads upon the Magellan spacecraft during aerobraking thro ugh the atmosphere of Venus are computed at off-design attitudes with a direct simulation Monte Carlo (DSMC) particle method. This method is not restricted to the assumption of collisionless flow normally emplo yed to assess spacecraft aerodynamics. Simulated rarefied flows at nom inal altitudes near 140 km and an entry speed of 8.6 km/s were compare d with simulated and analytic free-molecular results. Aerodynamic mome nts, forces, and heating for rarefied entry at all attitudes were 7-10 % below free-molecular results. All moments acted to restore the vehic le to its nominal zero-pitch, zero-yaw attitude. Suggested canting of the solar panels is an innovative configuration to assess gas-surface interaction during aerobraking. The resulting roll torques about the c entral body axis, as predicted in rarefied-now simulations, were nearl y twice that predicted For free-molecular flow, although differences b ecame less distinct for thermal accommodation coefficients well below unity. In general, roll torques increased dramatically with reduced ac commodation coefficients employed in the simulation. In the DSMC code, periodic free-molecule boundary conditions and a coarse computational grid and body resolution served to minimize the simulation size and c ost while retaining solution validity.