National Aeronautics and Space Administration Planetary Protection Office

Missions to Mars may be designated Category III, IVa, IVb, or IVc for planetary protection purposes, depending on their aims.

Category III missions to Mars (flybys and orbiters), as well as cruise stages, as stated in Section of NPR 8020.12D, shall avoid Mars impact at a probability no less than 0.99 for 20 years after launch and a probability no less than 0.95 for the period 20-50 years after launch.

All Category IV missions to Mars shall meet the following bioburden constraints, as deemed appropriate given the mission type and needs, and as approved by the NASA PPO.

The following table provides the bioburden values for Mars Category IVa, IVb, and IVc missions.

Table is adapted from Frick, A. F., Mogul, R., Stabekis, P., Conley, C. A., Ehrenfreund, P. Overview of Current Capabilities and Research and Technology Developments for Planetary Protection. Adv. Space Res. 54, 221-240.