High Performance Spectroscopic Observation from a CubeSat

Many operational and scientific CubeSat missions opportunities are contingent on the development of miniaturized spectroscopic or hyperspectral imaging instruments with very high spectral resolution. Such missions include profiling of processes and conditions in the upper atmosphere, exploring energetic inputs and responses in the upper atmosphere, atmospheric sounding, Doppler sensing of winds in the upper atmosphere, and hyperspectral earth monitoring for agriculture, resource management, oceanography, and disaster assessment. In addition to the challenge of achieving excellent optical performances in a miniaturized package, spectroscopic instruments for CubeSat missions must satisfy a range of challenging interface constraints: • Minimal use of expensive custom optics; • Affordable focal plane technology; • ConOps that efficiently utilize limited data link capacity; • Static instrument attitude (no slewing or scanning); • Stray light control in a small package; • No precision mechanisms; • Low power usage; and • Passive thermal stabilization. Experience reveals that no single miniature instrument concept can be optimized for all missions. Previous advances in miniaturized spectroscopic instruments have applied innovative spectral filter technologies, e.g. the linear variable filter (LVF) spectrometer and gas filter correlation radiometer (GFCR). In the following three examples, spectrometer and interferometer concepts have been dramatically miniaturized to enhance the resolution for CubeSat missions. Optical Profiling of the Atmospheric Limb (OPAL). This dispersive spectrometer with a multi-slit array and a volume holographic grating was developed for dynamic temperature profiling of the lower thermosphere from a CubeSat. OPAL is a snapshot hyperspectral instrument with very high spectral resolution and tradeoffs with respect to bandwidth and horizontal sampling. Split-field Etalon Doppler Imager (SEDI). A fixed-gap Fabry-Perot etalon provides picometer resolution of atomic emission lines suitable for measurement of winds and temperatures in the mid-thermosphere. Vertical profiles are obtained by image processing of the SEDI interferograms. Energetic Event Spectral Imager (EESI). This miniaturized spatial heterodyne interferometer can be built with COTS components. EESI supports hyperspectral imaging with very high etendue for low-light hyperspectral imaging (scanned mode) or collection of instantaneous wideband spectra of dynamic events (snapshot mode). Our presentation details the capabilities of these spectroscopic sensors and their applicability to future CubeSat missions