Novel solar soft X-ray imaging spectroscopy from a CubeSat platform

Amir Caspi ¹ Albert Shih ² Harry Warren ³ Daniel Seaton ⁴ James Klimchuk ² Thomas Woods ⁵ James Mason ⁵ Marek Steslicki ⁶ Szymon Gburek ⁶ Janusz Sylwester ⁶ Craig DeForest ¹

¹Planetary Science Directorate, Southwest Research Institute, Boulder, CO, USA
²Goddard Space Flight Center, NASA, Greenbelt, MD, USA
³Space Science Division, Naval Research Laboratory, Washington, DC, USA
⁴CIRES, University of Colorado, Boulder, CO, USA
⁵LASP, University of Colorado, Boulder, CO, USA
⁶Space Research Centre, Polish Academy of Sciences, Wrocław, Poland

We present a proposed small satellite pathfinder mission, the CubeSat Imaging X-ray Solar Spectrometer (CubIXSS), to measure spectrally-resolved, spatially-isolated soft X-rays (SXRs) from the quiescent and flaring Sun from a 6U CubeSat platform in low-Earth orbit during a nominal 1-year mission.

A critical observational gap exists from 0.2 to 3 keV ( 4–60 Å), where spectrally-resolved stellar observations are plentiful but have not been routinely made for the Sun in many decades. These SXR emissions provide crucial diagnostics of plasma temperature distributions, as well as elemental abundances that probe plasma origins over a wide range of temperatures, that are not available from observations at other wavelengths but are essential for understanding plasma heating, particle acceleration, and energy transport from magnetic reconnection processes in both solar flares and quiescent active regions.

The primary CubIXSS instrument is the Multi-Order X-ray Spectral Imager (MOXSI), a novel spectro-spatial imager utilizing a custom pinhole camera and Chandra-heritage X-ray transmission diffraction grating to provide full-Sun imaging spectroscopy. MOXSI covers the 0.2 to 10 keV ( 1–60 Å) passband with 0.25 Å FWHM spectral resolution and moderate spatial resolution of 25 arcsec FWHM, sufficient to isolate solar flares and active regions from their ambient surroundings. Additional pinholes with tailored filters provide non-dispersed images with coarse spectral information to seed analysis of the dispersed spectro-spatial images and for improved sensitivity to quiescent conditions. MOXSI’s unique capabilities enable SXR spectroscopy and corresponding temperature and elemental abundance diagnostics of individual flares and active regions over a spectral range never before accessed by any prior solar mission.

MOXSI is supported by low-noise, commercial off-the-shelf (COTS) SXR spectrometers enabling full-Sun SXR spectroscopy from 0.5 to 20 keV with 0.15 keV FWHM spectral resolution. Multiple detectors and tailored apertures provide sensitivity from deep solar minimum to >X5 flares.

CubIXSS is a pathfinder for larger SmallSats with improved sensitivity and spatial and spectral resolutions.