Clean rooms are highly controlled environments accessible only to trained personnel following strict and unambiguous cleanliness protocols. Representative standard NASA clean-room protocols include the following:

• During assembly, workers are required to wear full face shield suits;

• No human contact directly with spacecraft is permitted. Latex gloves are worn in the clean room, and spacecraft are not seeded with tracer organisms to facilitate monitoring;

• Cameras are used to observe and monitor assembly;

• Clean-room air passes through high efficiency particulate air (HEPA) filters and dehumidifiers to minimize airborne microbial contamination and corrosion, respectively;

• Surface particles are removed by vacuuming;

• Witness plates are regularly collected and stored;

• Contact between hardware and biologically relevant materials is minimized; and

• Surface areas of the spacecraft are monitored periodically for their microbiological burden, during and after assembly. Sterile cotton swabs are used to collect contaminating surface microorganisms, which are subsequently cultured and counted.

Unfortunately, clean rooms do not guarantee contamination-free assemblies. Mistakes happen, and clean hardware may not remain clean. Thus, good in-process cleaning procedures are necessary.

¹ Viking '75 Project, Pre-launch Analysis of Probability of Planetary Contamination, Volumes II-A and II-B, M75-155-01 and M75-155-02, Jet Propulsion Laboratory, Pasadena, Calif., 1975.