The Instruments and Capabilities of the Miniature X-Ray Solar Spectrometer (MinXSS) CubeSats

Abstract

The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Science Mission Directorate, with the main objective of measuring the solar soft X-ray (SXR) flux and a science goal of determining its influence on Earth’s ionosphere and thermosphere. These observations can also be used to investigate solar quiescent, active region, and flare properties. The MinXSS X-ray instruments consist of a spectrometer, called X123, with a nominal 0.15 keV full-width at half-maximum (FWHM) resolution at 5.9 keV and a broadband X-ray photometer, called XP. Both instruments are designed to obtain measurements from 0.5 – 30 keV at a nominal time cadence of 10 s. A description of the MinXSS instruments, performance capabilities, and relation to the Geostationary Operational Environmental Satellite (GOES) 0.1 – 0.8 nm flux is given in this article. Early MinXSS results demonstrate the capability of measuring variations of the solar spectral soft X-ray (SXR) flux between 0.8 – 12 keV from at least GOES A5–M5 ( ) levels and of inferring physical properties (temperature and emission measure) from the MinXSS data alone. Moreover, coronal elemental abundances can be inferred, specifically for Fe, Ca, Si, Mg, S, Ar, and Ni, when the count rate is sufficiently high at each elemental spectral feature. Additionally, temperature response curves and emission measure loci demonstrate the MinXSS sensitivity to plasma emission at different temperatures. MinXSS observations coupled with those from other solar observatories can help address some of the most compelling questions in solar coronal physics. Finally, simultaneous observations by MinXSS and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) can provide the most spectrally complete soft X-ray solar flare photon flux measurements to date.

Joint X-Ray, EUV, and UV Observations of a Small Microflare

“…But again it should be noted that GOES/XRS was not designed to be useful for these small fluxes. Future observations with NuSTAR that overlap with other softer X-ray spectrometers, such as MinXSS-2 (Moore et al 2018) or MaGIXS (Kobayashi et al 2018), might help to resolve the true multi-thermal emission of these small microflares over this energy range.…”

Analysis of Quiescent Corona X-ray Spectra from SphinX During the 2009 Solar Minimum

“…It is interesting to speculate on the low level of X-ray emission for the present (2019) minimum, between Cycles 24 and 25, if observed by a SphinX-like instrument. Results from the MinXSS-2 mission, launched in late 2018 (Moore et al, 2018), are currently unavailable, but with its spectral resolution of 150 eV it would be interesting to compare temperatures and emission measures from this study. If the present apparent trend for ever deeper solar minima is sustained, there is clearly a need for a highly sensitive instrument to monitor the Sun's soft X-ray emission during such periods.…”

Future Prospects for Solar EUV and Soft X-Ray Spectroscopy Missions

“…SDDs are more expensive but allow higher count rates and slightly better spectral resolution. Spectral coverage is typically 1-20 keV and resolution is about E/ E = 30-50, which is sufficient to resolve spectral features from which element abundances can be derived (Dennis et al, 2015;Moore et al, 2018).…”

“…In terms of solar missions, the SphinX instrument (Gburek et al, 2013) on board the Russian CORONAS-Photon mission used an earlier version of the AMPTEK detector, while the X-123 was flown on the MinXSS-1 and 2 Cubesats (Moore et al, 2018) in 2016 and 2018, although the latter failed before data could be obtained. New missions are described in section 9.1.…”