A Balloon-Borne Infrared Coronagraph and Spectropolarimeter for Magnetic Field Measurements of the Solar Corona

We propose to develop a multi-wavelength infrared coronagraph and spectropolarimeter for NASA’s scientific balloon program and eventual use in space. The Coronal Spectropolarimeter for Airborne Infrared Research (CORSAIR) will make continuous long-duration measurements of coronal plasma and magnetic fields by observing five emission lines at 1.1, 1.4, and 3.9 microns, including a density sensitive Fe XIII line pair, a temperature sensitive Si IX/X line pair, and a He I line for probing cooler plasma. CORSAIR will measure line-of-sight magnetic field strength through the longitudinal Zeeman effect and plane-of-sky magnetic field direction through the saturated Hanle effect, as well as plasma temperature, density, and line-of-sight, plane-of-sky, and non-thermal velocity. Our primary science goals explore the transition of coronal structures between closed and open field and the role of waves and flows in transporting mass and energy in coronal magnetic fields. Our development plan calls for a 1 day commissioning flight in September 2024 and a 1–2 week science flight over Antarctica in late 2026, addressed in a future proposal. This proposal describes the instrument design and development and the commissioning flight.

Recent state-of-the-art ground-based instrumentation has expanded the infrared window for coronal spectropolarimetry, while the 2017 and 2019 AIR-Spec eclipse flights have demonstrated that high-altitude infrared remote sensing is a promising new method for measuring coronal plasma and magnetic fields. CORSAIR builds on this work, but its observations are distinguished by their (1) duration: continuous observations over several days cover the timescales for flux emergence, (2) field of view: the global scale allows us to follow the large-scale evolution of the corona, and (3) altitude: less atmospheric absorption means greater sensitivity and fewer corrections to apply. CORSAIR will lead to a major advance in understanding the inner corona while serving as a prototype for future space instrumentation.

CORSAIR is a coronagraph, polarimeter, and grating spectrometer that provides two-dimensional spectral imaging of the full polarization state of the corona up to 1 solar radius from the limb. The spectrometer includes multiple slits in order to allow the spectral dimension and both spatial dimensions to be acquired simultaneously. By operating in multiple orders, the polarimeter and spectrometer measure each of the five emission lines with similar sensitivity and resolving power. Lines are selected by refocusing the instrument and tilting the grating. CORSAIR will be developed by Smithsonian Astrophysical Observatory (SAO), in collaboration with the NCAR High Altitude Observatory (HAO) and the University of Hawaii Institute for Astronomy (UH IfA). HAO has extensive experience designing ground-based coronagraphs and polarimeters, and UH IfA is currently developing a ground-based multi-slit coronal spectropolarimeter that targets many of the CORSAIR lines. SAO will contribute expertise in coronal spectroscopy and high-altitude (airborne, rocket, and satellite) instrumentation.

Recent developments in sensor technology have dramatically increased access to the mid-infrared wavelengths that are uniquely suited to measuring the coronal magnetic field. The storage of magnetic free energy in coronal structures has been recognized for decades, and the build-up of energy over long time scales and its rapid release in the form of flares and CMEs are defining characteristics of activity on the sun and sun-like stars. The prospect of following the global coronal magnetic field evolution continuously over time scales from tens of hours to weeks holds great promise for advancing our understanding of coronal energy storage and the onset of instabilities that result in energy release.

Enabling lower cost innovative remote sensing instrument development from concept through breadboard and demonstration

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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