NASA Planetary Protection Categories and Requirements

The NASA Planetary Protection Categories and Requirements document is meant to guide space mission development through developing risk assessments associated with the contamination of a NASA mission. The document explains mission types, different planetary bodies, types of bodies, and their associated categories.

NASA establishes criteria for each NASA-sponsored payload. Four risk classification levels (A thru D) are defined in the NASA Procedural Requirements (NPR). For example:

Planetary Protection addresses microbial contamination of the solar system by spacecraft that we launch from Earth (forward contamination). This contamination must be prevented in order to preserve the integrity of exploring the solar system; celestial bodies that may have once held an environment suitable for life (e.g., Mars and outer planet icy bodies) are especially vulnerable. Likewise, extraterrestrial contamination of the Earth and Moon (backward contamination), by way of sample return missions, must be prevented. We must approach with caution and preparedness in bringing unknown and potentially dangerous biological materials back to Earth.

To address both types of contamination concerns, a Planetary Protection category for each mission is assigned according to the combination of the type of encounter a spacecraft may have and the nature of its destination (e.g., lander and moon). If a target body has the potential to support life, a spacecraft going there must undergo stringent cleaning and sterilization processes, and greater operating restrictions. Likewise, samples from planetary bodies that have the potential to support life must be sealed and sterilized prior to Earth-entry.

It is anticipated that the Psyche mission will be a Category II.

This document was adapted from

For more information, visit

Interested in learning more about NASA’s Psyche Mission?

The NASA Psyche Mission Innovation Toolkit includes a series of free online courses based on the real-world challenges and skills associated with the Psyche mission’s science, engineering, technology, and teamwork. Click below to learn more:

NASA Psyche Mission Innovation Toolkit