MARS ENVIRONMENTAL SURVEY PROBE AEROBRAKE PRELIMINARY DESIGN STUDY

The objective of this study is to design aerobrakes for the Mars Environmental Survey (MESUR) vehicles. To contain cost, existing flight-certified materials are considered for the structure and heatshield. Since the probes enter the atmosphere directly, the heatshields had to survive entry during duststorm conditions. A slightly modified Viking forebody shape, consisting of a blunted 70-deg cone, is used. An aluminum honeycomb shell is used for the structure. For the nominal 7-km/s entry, the heatshield material used on the Vikings (a silicone elastomeric charring ablator, SLA-561) was found to be lightest, yielding an aerobrake mass fraction of 13.2%. For the extreme case of entry at 9 km/s, the stagnation region heatshield consisted of the medium-density ablator AVCOAT-5026, used on the Apollo capsules, and SLA-561 was used on the conical skirt. The aerobrake mass fraction for the 9-km/s entry was 18%. The penalty resulting if a single conservatively designed aerobrake were used for both entry velocities could reach 4.8% of the entry mass at 7 km/s. Therefore, it is recommended that separate aerobrakes be designed for probes entering at 7 km/s and at 9 km/s.