Life support systems for manned exploration missions are becoming increasingly complex. In next-generation manned space exploration, closed-loop control of all life support systems must be established, particularly for missions requiring extended human occupation of space or the lunar or martian surface. To accomplish this control, sensors must be developed that are capable of monitoring and feeding back information on the concentrations of a number of chemical and biochemical substances. Two critical sets of variables that must be monitored are: oxygen concentration and flow in crew air supply (both in capsules and in suits and masks); carbon dioxide, oxygen, and moisture content in hydroponic or other food- and oxygen-producing life support systems.
The systems we are developing are based on the use of conventional fibers and sources, but utilize custom wavelength division multiplexers in their optical signal processing sections, and non-standard porous optical fibers in the optical sensing (optrode) elements. Porous optical fibers, when “doped” with indicator dyes, can be made to exhibit optical properties that undergo remarkably large changes in the presence of chemical substances (analytes) to which the indicator dyes respond. These changes take place when the analytes diffuse into the pores of the fibers, and interact with the sensor dyes. By analyzing the data from both “native” and dye-doped fibers, sensor systems can be designed that will achieve high-sensitivity, low-drift measurements of chemical concentration. The use of custom high-efficiency wavelength division multiplexers allows the sensing systems to be very lightweight and rugged.
We will present preliminary experimental results on systems designed to demonstrate sensor operation in regenerative food production and crew air supply applications.