Design and Development of the Compositional InfraRed Imaging Spectrometer (CIRIS) for Outer Planet and Primitive Body Missions

The CIRIS instrument is a Fourier Transform (FT) spectrometer that utilizes a constant-speed rotating refractor to alter the path length of incoming light beams, in place of the linear moving mirror used by traditional FT spectrometers. At any given instant, the path length difference is governed by angle of incidence of the beam onto the refractor, as Snell's law predicts the refraction angle. This design allows for a compact and robust device, and eliminates the need for a constantly accelerating/ decelerating mirror. This, along with the intrinsic radiation-hardness of an FT spectrometer, make the instrument ideal for spaceborne measurements from near-IR to thermal-IR wavelengths (1-12μm). The refractive scanning design was developed and proven for terrestrial and airborne use by Designs & Prototypes, Ltd., under contracts with the US Army Edgewood Chemical and Biological Center (ECBC), and with CSIRO in Australia. Here we present the design for spaceflight applications, and results from laboratory testing and development. Testing efforts include the development of low-noise electronics, lab experiments on radiation noise immunity, and thermal/ vacuum testing of our spaceflight breadboard unit. The wavelength range and radiation hardness of this instrument can allow compositional analysis of many planetary and primitive body surfaces.