Miniature gas sensor for monitoring biological space environments

摘要

A versatile gas sensor for use in gravitational studies and/or long-term monitoring of biological systems in space is described. The sensor combines two diode lasers in a compact, low power package for quantitative, simultaneous measurements of oxygen, carbon dioxide and potentially, water vapor. Wavelength modulation spectroscopy(WMS) combined with digital signal processor (DSP) control allows this system to meet the stringent weight and power restrictions of a space-borne sensor. The sensor, configured for measurements in plant growth chambers, exhibits a very high level of precision for long-term measurements, with an uncertainty in CO_2 concentrations of better than 3 parts per thousand (ppth), and about 5 ppth for ambient oxygen, all at 1 Hz. Allan variance measurements indicate that increasing the averaging time to 100 sec will improve the precision to 0.3 ppth. The dynamic range for CO_2 detection exceeds four orders of magnitude.