[77]

Performance Evaluation of a Laboratory Test Bed for Planetary Biology. N. A. Thomas1, P. Todd1, G. W. Metz1, H. Platt1, A. Kurk1, D. J. Thomas2, 1SHOT, Inc., Greenville, IN, and 2Lyon College, Batesville, AR.

   A laboratory test bed was constructed for the simulation of planetary environments for biological experimentation.  The test bed consists of the following subsystems: a 1,000 W xenon arc lamp with an “AM0” filter to simulate solar irradiance in space, an 8 ft3 cryogenic thermal cabinet capable of cooling to -135oC and heating to +50oC using evaporating nitrogen and resistive heaters, a fused silica cylinder that transmits the full solar spectrum and can be evacuated to <10 mbar through stainless steel end caps, a 500-gal liquid nitrogen storage tank, a cylinder of pressurized support gas, and a control system that automatically cycles the interior of the cylinder through a Mars daily cycle, for example.  Biological samples placed in the quartz cylinder are typically mixed with simulated planetary regolith.  During initial operation the test bed was used for preliminary biological experiments designed to test concepts of ecopoiesis. The light and temperature profiles matched those of Mars near the equator at the vernal equinox.  The test bed was cycled daily between -80oC and +26oC following a published temperature curve.  The atmospheric pressure on Mars is 7-10 mbar and the day length is 24.6 hours, but internal pressure of 100 mbar and day length of 24.0 hours were used for early biological experiments.  The gas composition used was 0.139% O2, 1.615% Ar, 2.760% N2 with the balance CO2.  The atmosphere was saturated with water by the daily injection of a few grams of (liquid) distilled water into the atmosphere (water boils at 49oC at 100 mbar).  The measured visible (photosynthetically active) photon flux was 1100 µmoles-m-2-s-1 in direct light and 12 µmoles-m-2-s-1 in the shaded interior of the cylinder.  This corresponds closely to values determined for the Martian surface and is consistent with the 590 W-m-2 total energy flux. Pressure, illumination, cabinet temperature and regolith temperature were recorded during operation of the test bed for 1, 8, 14 and 35-day periods.  Under daily cycling liquid nitrogen was consumed at approximately 1600 liters/week and was exhausted safely to the exterior of the laboratory.