Chemical sensors for space applications

There will be a great need for a wide variety of chemical analyses, both for biomedical experimentation and for the monitoring of water and air recycling processes on Space Station Freedom and later long-term space missions. The infrequent logistics flights of the Space Shuttle will necessitate onboard analysis. Chemical sensors offer several advantages over conventional analysis onboard a spacecraft. They require less crew time, space, and power. A chemical sensor consists of a selector which selectively interacts with the analyte present in a mixture of substances, and a transducer which produces an electric signal in response to the interaction of analyte and selector. The transducer signal thus provides a quantitative and selective measurement of the analyte. Types and requirements for chemical sensors to be used in biomedical experimentation and monitoring of water recycling during long-term space missions are discussed. With chemical sensors, a wide variety of analytes can be determined selectively without separation steps. In principle, chemical sensors can provide (near) real-time monitoring of many important analytes. In some cases they can even provide continuous monitoring of such analytes. The sensors, and even the ancillary instruments, are small compared to conventional analytical instruments. Their power consumption is low. Sensor measurements do not require extensive sample treatment before analysis. In most cases a sensor can simply be inserted in, or be attached to, the organism; or be placed in the water flowing through the water recycling system. Since the sensor signal can usually be provided in digitized form, rapid transmission to the ground is possible. The use of sensors thus provides an efficient use of the scarce resources of crew time, pressurized volume, and power.