Contamination Control for Ultra-Sensitive Life-Detection Missions

"This study report summarizes technological developments in science-required contamination
control for cost-capped, life-detection missions in the Solar System. Technology advances focus
on developing implementable strategies to restrict contamination of the spacecraft and instruments
by the launch vehicle hardware. Secondary bake out operations during cruise further
reduce molecular contaminants down to femtomolar levels in the sample path.
The study validated a full-spacecraft, deployable barrier design as an effective strategy to
isolate the spacecraft from the pre-launch processing and launch environment (e.g., fairing
acoustic materials). It accommodates late mounting of RTGs and other required prelaunch
activities. A new, high-fidelity physics, contamination-transport model for particles (including
cells and their parts) and science-relevant molecules (e.g., possible biomolecules) was developed
to validate the barrier concept. Importantly, this model takes into account the physics of
extremely clean surfaces achieved by the best traditional contamination engineering. The ability
to deal with very low levels of particulate and molecular contamination makes this model
unique among standard contamination modeling approaches. Modeling also demonstrated that
a high-temperature bake out during interplanetary cruise of the sample collector that comprises
the largest surface area in the sample path for an Enceladus orbiter reference mission, was
extremely effective. This study included the evaluation of other details necessary for an effective
contamination control strategy for life detection missions including feasibility of achieving parts
per trillion level cleanliness for semi-volatile hydrocarbons in nitrogen purge gas, identification of
launch vehicle services required for the baseline contamination control, and defining additional
contamination control measures to be taken during launch operations.
Key results of the study are: • New spacecraft barrier design that accommodates RTGs is readily
cleanable and repairable. Deployment of a 1/3 scale model was successfully demonstrated. •
The barrier reduces particle contamination (likely biological) from fairing to spacecraft by 1e-2
to 1e-3. • On-cruise bake-out of critical surfaces significantly reduced molecular contamination
(by as much as 1e-12). Subsequently, the probability of a surface contamination particle being
transported to an instrument by an ice particle is less than 5.1e-5 (for microbes specifically,
4.39e-10).
The report concludes that a full-spacecraft barrier designed specifically for life-detection missions
that require stringent control of particulate and molecular contaminates is an effective
means of mitigating risks of false positive and negative results for life signature investigations.
Further, secondary cleaning steps for critical sections of the sample path can be highly effective
at reducing molecular contaminants to low femtomolar levels."