Periklis Papadopoulos

Heatshield Erosion in a Dusty Martian Atmosphere

The effects of dust particle impacts on the erosion of the forebody heatshield were calculated for a 26 m diameter aerobraking vehicle entering a dusty Martian atmosphere at 8600 m/s. An explicit, thin-layer, Navier-Stokes code was used to compute the dustless flowfield about the vehicle for the actual Martian atmospheric composition. The deceleration and melting of 1-19/on diameter dust particles within the forebody shock layer were computed. All particles began vaporizing shortly after entering the shock layer, but most survived to hit the heatshield surface. The two different heatshield materials considered were Shuttle ceramic tiles and the ablator used on the Apollo capsule. For a vehicle with a ballistic coefficient of 200 kg/m2, the heatshield surfaces experienced an average of about 7 mm of surface erosion. For the ablator, the increase in the forebody thermal protection mass was 29%, or about 1.3% of the vehicles mass. This modest mass penalty does not compromise the use of aerobraking at Mars.

Simulation of Galileo probe descent through Jovian clouds

One of the instruments on-board the Galileo probe that entered Jupiter’s atmosphere was a Nephelometer. This instrument measures the light scattered from cloud particles, and, by comparing the results to model particles, the particle size, phase, and number density can be determined. Unfortunately, some of the results obtained from the Nephelometer can not be explained by any known particles. One hypothesis for this result is that the Nephelometer instrument, part of which extends outward from the probe body, modifies the flow in such a way to change the particle distribution in the measurement region. To investigate this hypothesis, a three-step simulation has been performed. First, the gas-phase flow around the orbiter is modeled using a Navier-Stokes solver. Second, particles are tracked through the numerically-determined flow using a particle-trajectory simulator. Third, The trajectories of thousands of particles are analyzed to determine the number density in the vicinity of the Nephelometer instrument. ‘The results of this study reveal that the number density in the vicinity of the Nephelometer measurement region is affected by the portion of the Nephelometer that extends into the flow. These results are currently being used to correct the data sent back from the Nephelometer probe. Simulations such as that performed here might be used in the future to aid in the design of similar planetary-probe instruments.