The survival of micro-organisms in space. Further rocket and balloon-borne exposure experiments.

This report describes the results of survival studies of terrestrial micro-organisms exposed directly to the space environment on two balloons and in two rocket flights. The work is part of a program to develop techniques for the collection of micro-organisms in the size range of micrometeorite particles in space or non-terrestrial atmospheres, and their return to earth in a viable state for further study. Previous survival studies were reported (J. Hotchin, P. Lorenz and C. Hemenway, Nature 206 (1965) 442) in which a few relatively large area samples of micro-organisms were exposed on millipore filter cemented to aluminum plates. In the present series of experiments, newly developed techniques have resulted in a 25-fold miniaturization resulting in a corresponding increase in the number of experiments performed. This has enabled a statistical evaluation of the results to be made. A total of 756 separate exposure units (each approximately 5 x 5 mm in size) were flown in four experiments, and organisms used were coliphage T1, penicillium roqueforti (THOM) mold spores, poliovirus type I (Pfizer attenuated Sabin vaccine strain), and bacillus subtilis spores. The organisms were deposited either by spraying directly upon the vinyl-coated metal units, or by droplet seeding into shallow depressions in the millipore filter membrane-coated units. Groups of units were prepared comprising fully exposed, inverted (screened by 2 mm of Al), and filter-protected organisms. All of these were included in the flight set, the back up set, and a laboratory control set. The altitude of the exposures varied from 35 km in the balloon experiments to 150 km in the rocket experiments. Times of exposures at altitude were approximately 6 hours for the balloon flights and about 3 minutes for the rocket experiments.