Control Electronics for High Wavelength Accuracy in a Nanosatellite Hyperspectral Imager

Nanosatellite-compatible miniaturized hyperspectral imagers must achieve excellent wavelength accuracy in order to provide data suitable for use in scientific missions. This paper presents the gap control of the Fabry-Perot
interferometer (FPI) used in the hyperspectral imager of the nanosatellite Aalto-1. The imager uses the FPI as a variable band-pass filter by varying the gap between the mirrors. The distance between the mirrors is estimated by measuring the capacitance between three sets of electrodes positioned around the mirrors. Without temperature compensation, the gap controller was not able to keep the temperature drift of the gap within the specified limit of 0.3 nm/°C. The gap control loop was broken down into potential drift contributors, and the worst-case instability is estimated. The measured drift was larger than the estimated drift, probably due to deformation of the FPI substrates. Using a temperature compensation function in the instrument microcontroller software, the resulting drift was reduced by more than an order of magnitude, satisfying the requirement.