MRO approach to planetary protection compliance

The Mars Reconnaissance Orbiter (MRO) Project will be the first United States Mars orbiter to take the compliance option of total spores on the spacecraft less than 5\cdot10^5 instead of the probability of accidental impact less than 0.01, under the National Aeronautics and Space Administration's planetary protection regulations. In addition, MRO has received a special modification of the total spore requirement so that the allowed number of spores after Mars atmosphere entry heating is 5\cdot10^5. The NASA PP standard requirement is "at launch." This modified rule permits the use of a breakup and burn-up analysis performed by Lockheed Martin Astronautics, which has demonstrated that all of the external surfaces and most of the orbiter is ablated away and/or heated to 500°C (NASA PP specification for sterility).^1 Dry heat microbial reduction has been employed to reduce the estimated spore burden (based on NASA PP specifications for burden density) on spacecraft hardware which is not rendered sterile by the entry and can tolerate the process. Finally, proxy assays have been performed to reduce the estimated spore burden for selected hardware items which are not sterilized by the entry and cannot be dry heat processed. The approach to PP compliance will be discussed in more detail. The degree of compliance will be presented. ^1The breakup and burn-up analysis is the subject of another paper in this session.