Larry A. Roe

Dynamic Temperature Fields under Mars Landing Sites and Implications for Supporting Microbial Life

While average temperatures on Mars may be too low to support terrestrial life-forms or aqueous liquids, diurnal peak temperatures over most of the planet can be high enough to provide for both, down to a few centimeters beneath the surface for some fraction of the time. A thermal model was applied to the Viking 1, Viking 2, Pathfinder, Spirit, and Opportunity landing sites to demonstrate the dynamic temperature fields under the surface at these well-characterized locations. A benchmark temperature of 253 K was used as a lower limit for possible metabolic activity, which corresponds to the minimum found for specific terrestrial microorganisms. Aqueous solutions of salts known to exist on Mars can provide liquid solutions well below this temperature. Thermal modeling has shown that 253 K is reached beneath the surface at diurnal peak heating for at least some parts of the year at each of these landing sites. Within 40 degrees of the equator, 253 K beneath the surface should occur for at least some fraction of the year; and, within 20 degrees , it will be seen for most of the year. However, any life-form that requires this temperature to thrive must also endure daily excursions to far colder temperatures as well as periods of the year where 253 K is never reached at all.

Investigation of biological, chemical and physical processes on and in planetary surfaces by laboratory simulation

Abstract The recently established Arkansas–Oklahoma Center for Space and Planetary Science has been given a large planetary simulation chamber by the Jet Propulsion Laboratory, Pasadena, California. When completely refurbished, the chamber will be dubbed Andromeda and it will enable conditions in space, on asteroids, on comet nuclei, and on Mars, to be reproduced on the meter-scale and surface and subsurface processes monitored using a range of analytical instruments. The following projects are currently planned for the facility. (1) Examination of the role of surface and subsurface processes on small bodies in the formation of meteorites. (2) Development of in situ sediment dating instrumentation for Mars. (3) Studies of the survivability of methanogenic microorganisms under conditions resembling the subsurface of Mars to test the feasibility of such species surviving on Mars and identify the characteristics of the species most likely to be present on Mars. (4) The nature of the biochemical “fingerprints” likely to have been left by live organisms on Mars from a study of degradation products of biologically related molecules. (5) Testing local resource utilization in spacecraft design. (6) Characterization of surface effects on reflectivity spectra for comparison with the data from spacecraft-borne instruments on Mars orbiters.

DEVELOPMENT OF A MEMS-BASED HEALTH-MONITORING MODULE FOR SPACE INFLATABLE STRUCTURES

Inflatable structures are expected to become increasingly important in space solar power and other space applications due to their low mass and low cost. Structures are susceptible to damage in orbit from effects such as radiation and small holes punctured by micrometeoroi ds. Health monitoring of the structures is important for knowing the condition of the structure and to provide early warning of impending failure. Traditional sensor packages can be bulky, expensive, and rigid, making them unsuitable for the flexible surfaces and contours of inflatable structures. We are currently developing a MEMS-based sensor module that is of low cost, low mass, and flexible. To achieve low cost, the sensor suite utilizes commercial-off-the-shelf sensors for monitoring physical quantities such as temperature, strain, pressure, and acceleration. The sensors are packaged together on a flexible polyimide substrate providing ample flexibility. The double-sided substrate consists of copper traces allowing backside leads and contacts. Through matching contacts on the surface of the inflatable structure, it will be possible to install the healthmonitoring module by simple attachment methods. Integration of sensors and actuators was investigated and initial assessments were made. -The incorporation of supporting electronics with flexible actuators will move the module toward autonomy and active control of the inflatable structure.

Solid State Gas Generator for Small Satellite deorbiter

We present the first MEMS Solid State Gas Generator (SSGG) for use as a deorbit technology, in conjunction with inflation balloons, for Small-Satellites (<180kg mass). The total system, named the Solid State Inflation Balloon (SSIB), is being designed as a simple, reliable, scalable, low-cost, non-propulsive deorbit system. Small-Sats in Low Earth Orbit (LEO) are required, through multi-national understanding, to deorbit within 25 years. The SSIB enhances aerodynamic drag by inflating a balloon at the spacecrafts end-of-life. The SSGG is composed of a 2D addressable array of Sodium Azide (NaN3) crystals on a glass substrate. The crystals are contained in wells formed by a thick-film of epoxy (SU-8). Under each well is a resistive heater that is selectively addressed using Metal-Insulator-Metal (MIM) diode networks. When heated to above 350 °C, the NaN3 spontaneously decomposes to generate the N2 gas in time scales on the order of 10 milliseconds. Each well can be designed with a typical volume of 10−15 m3 to 10−6 m3 of NaN3. The effectiveness of the system has been numerically evaluated for 1U, 2U and 3U CubeSats. The deorbit time for these three spacecraft from a 550km altitude has been calculated to be 118, 236, and 355 days respectively, independent of initial inclination.