Sensor technology will gain in particular from nanotechnological developments. Out of the multiplicity of different sensor systems in space technology, only a few examples are described below, where nanomaterials offer significant application potentials.
Gas Sensors - Schottky Diodes, Resistive Sensors and Electrochemical Sensors
Gas sensors are used in a wide area of technical and scientific space applications, among other things for the detection of hydrogen leakages in rocket engines, for the measurement of the oxygen content in upper atmosphere layers, or for the monitoring of the air quality in manned space systems. In principle, three different gas sensors are used for space applications:
• Schottky diodes (e g. based on SiC),
• Resistive sensors (e.g. polymer films),
• Electrochemical sensors (e.g. based on tin oxide).
Electrochemical Sensors Made with Nanomaterials and Nanopowder Coatings
Regarding the employment of nanomaterials, in particular, electrochemical sensors are concerned. Miniaturized electrochemical gas sensors with sensitive metal oxide coatings (e.g. SnO2) are energy saving and can be easily integrated into CMOS circuits. The use of nanopowders for sensor and electrolyte coatings offers, in principle, advantages both regarding the production process (reduced sintering temperatures, which allow ‘co-firing’ of metals and ceramics) and the sensitivity and robustness of the sensors by improved ionic conductivity. By variation of the working temperature of the electrode or the electrolyte material, different gases can be detected (e.g. H2, CO2, NOx, CO or hydrocarbons). As electrolyte membranes ZrO2 or YSZ are, for example, used.
Electrochemical Gas Sensors Used in Space and Potential Industry Spin-Offs
Electrochemical gas sensors for applications in space are developed, for example, by the company Escube in Germany. For the production of the electrolyte membranes, sub micron powders (average particle size 200 nm) are used. Schottky diodes, which change their electrical conductivity by absorption of gas molecules, can be used in particular for the detection of hydrogen or hydrocarbons under the harsh space conditions. The automobile industry is likewise interested in gas sensors, so spin-off effects from space technology could arise in this area.
Sun Sensors Made from Nanomaterials such as Nanoporous Silicon
Another application for nanomaterials in sensor technology is sun sensors, on the basis of nanoporous silicon. Advantages of nanoporosity are, for example, decreased reflection losses and improved quantum yields. A prototype of a miniaturized sun sensor with use of nanoporous silicon has been developed in the frame of a Spanish nanosatellite project, under the leadership of the Instituto Nacional de Técnica Aerospacial.