Planetary Protection

The U.S. has obligations under the international 1967 Outer Space Treaty to explore space in a responsible manner that avoids the harmful contamination of celestial bodies while also not adversely affecting Earth’s environment with the return of any extraterrestrial samples. To help meet these obligations, NASA’s Office of Planetary Protection draws up cleanliness standards known as planetary protection requirements. These requirements ensure preservation of the integrity of scientific measurements made during solar system exploration by minimizing the chance that microbes or other organic material brought from Earth could be confused with local materials.

Planetary protection categories range from I to V, extending from the fewest protocols to the most. Outbound missions to celestial bodies that may have once held an environment suitable for life – including Mars and outer solar system icy bodies such as Jupiter’s moon Europa – fall into Planetary Protection Category III or IV.

Although the asteroid Psyche is not currently considered to be a body that would be a target for future biological study, the Psyche spacecraft is designated as a Planetary Protection Category III mission because it is flying by Mars for a gravity assist. The mission is required to demonstrate a probability of 99% or higher of avoiding impact with Mars for 20 years after launch, and 95% for a period of 20 to 50 years post-launch. When the Psyche mission concludes, the spacecraft’s disposal orbit will consist of a long-term, non-impacting trajectory.

To meet NASA’s cleanliness standards, engineers assembled the Psyche spacecraft in a clean room. Environmental conditions within the clean room are strictly monitored, and air filters are used that limit the size and number of dust particles. The surfaces and floors of the clean room are frequently treated with strong cleaning solutions to kill and remove living microbes. Mission hardware, including the tools used for spacecraft assembly, is cleaned using techniques that have proven effective on many previous missions without damaging the spacecraft. Technicians working in the clean room must wear “bunny suits,” face masks, hair covers, and latex gloves. Before entering, personnel step into an “air shower” that blows stray particles off the outside of their garments.