SIMULATED RAREFIED AERODYNAMICS OF THE MAGELLAN SPACECRAFT DURING AEROBRAKING

Aerodynamic loads upon the Magellan spacecraft during aerobraking through 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 employed to assess spacecraft aerodynamics. Simulated rarefied flows at nominal altitudes near 140 km and an entry speed of 8.6 km/s were compared with simulated and analytic free-molecular results. Aerodynamic moments, forces, and heating for rarefied entry at all attitudes were 7-10% below free-molecular results. All moments acted to restore the vehicle 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 central body axis, as predicted in rarefied-now simulations, were nearly twice that predicted For free-molecular flow, although differences became less distinct for thermal accommodation coefficients well below unity. In general, roll torques increased dramatically with reduced accommodation 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 cost while retaining solution validity.