The Biology Instrument for the Viking Mars Mission

Two Viking spacecraft have successfully soft landed on the surface of Mars. Each carries, along with other scientific instruments, one biology laboratory with three different experiments designed to search for evidence of living microorganisms in material sampled from the Martian surface. This 15.5-kg biology instrument which occupies a volume of almost 28.3 dm3 is the first to carry out an in situ search for extraterrestrial life on a planet. The three experiments are called the pyrolytic release, labeled release, and gas exchange. The pyrolytic release experiment has the capability to measure the fixation of carbon dioxide or carbon monoxide into organic matter. The labeled release experiment detects metabolic processes by monitoring the production of volatile carbon compounds from a radioactively labeled nutrient mixture. The gas exchange experiment monitors the gas changes in the head space above a soil sample which is either incubated in a humid environment or supplied with a rich organic nutrient solution. Each experiment can analyze a soil sample as it is received from the surface or, as a control, analyze a soil which has been heated to above 160C. Each instrument has the capability to receive four different soils dug from the Martian surface and perform a number of analysis cycles depending on the particular experiment. This paper describes in detail the design and operation of the three experiments and the supporting subsystems

The angular spectrum of dyadic green\u27s function in 3-D scattering environments

A rigorous representation of the dyadic Green\u27s function of the 3-D vector wave equation is derived between two disjoint communication volumes with arbitrary external scattering. The resulting expression is a double-integral of two plane waves multiplied with a dyadic kernel called the double-angular spectrum of the system. The two plane waves are the wave components traveling in various directions on the transmit and receive sides, respectively, and the dyadic spectrum, which is composed of orthogonal vector spherical harmonics, describes the waves\u27 interaction strength and polarization change. The derived DGF representation offers valuable physical insights and provides a rigorous mathematical framework that potentially can facilitate other electromagnetic propagation-related studies. As the core of this framework, the dyadic spectrum is numerically investigated in a model system with random scattering. The results bring to light many insightful characteristics on the statistical behaviors of the wave propagation between the communication volumes