VERIFICATION OF THE EFFICACY OF SPACECRAFT STERILIZATION

The possibility that terrestrial micro-organisms can survive decontamination and be ejected into the environment of planets emphasizes the need for control of sterilization, and the development of standards based on models made of relevant materials, which can be carefully investigated. Control of sterilization can be by physical, chemical or biological (bacteriological) means, depending on the purpose; bacteriological methods are the most precise and most generally useful. Test objects should be artificially infected by cultures of micro-organisms which are highly resistant to the sterilizing agent being tested and which are of high stability. To ensure reliable sterilization the density of contamination of test objects should be 10–100 times the natural level of contamination. The nature of the surface on which the test micro-organism is placed affects the efficacy of sterilization owing to differences in heat transmission or sorption of chemical disinfectants. The role of the recovery medium is also important. Physical and chemical methods are particularly valuable as indicators of efficacy of sterilization, e.g. the use of chemical indicators of temperature in heat sterilization. Results by various methods of control are in good agreement, but improvements in techniques are still necessary to make spacecraft sterilization more reliable.