Solar Cycle Studies for the Miniature X-ray Solar Spectrometer CubeSat Missions (MinXSS)

OBJECTIVES. The Miniature X-ray Solar Spectrometer (MinXSS) program is a successful science CubeSat mission for the H-TIDeS LCAS program, and we propose to extend the MinXSS studies with a second launch in December 2016 with improved instrumentation for a new 4-year mission. The original MinXSS-1 mission objectives are to better understand the energy distribution of solar flare soft X-ray (SXR) emissions and its impact on Earth’s ionosphere, thermosphere, and mesosphere (ITM). These studies, currently funded through 2016, focus on the solar SXR variability of active region evolution and flares during the MinXSS-1 six-month mission, modeling of the solar SXR variability, and understanding how the solar SXR energizes Earth’s ionospheric E-region (80-150 km). The MinXSS-2 mission with its longer 4-year life will extend these studies during the declining phase of solar cycle 24, cycle minimum, and the rising phase of solar cycle 25. MinXSS will enhance these original studies during these different solar cycle phases by characterizing the differences in (1) the active region heating / abundance, (2) flare energetics, and (3) solar forcing in Earth’s upper atmosphere. METHODOLOGY. MinXSS is a solar-oriented, 3-axis-controlled, 3-unit CubeSat to observe the solar SXR spectrum between 0.6 and 30 keV (0.04 and 2 nm). The X-ray spectrometer on MinXSS has a nominal spectral resolution of 0.15 keV full width half maximum (FWHM). The capabilities of this X-ray spectrometer have been flight-proven on MinXSS-1 and also previously on sounding rocket flights in 2012 and 2013. An improved version of this X-ray spectrometer is on MinXSS-2. The other major technology on MinXSS is the Attitude Determination and Control System (ADCS) from Blue Canyon Technologies (BCT); the BCT 0.5-unit ADCS has been flight proven on MinXSS-1 with precision solar pointing to ~10 arc-seconds. The MinXSS-1 was launched in December 2015 to the International Space Station (ISS) and deployed from the ISS on May 16, 2016. Starting from the ISS altitude of ~400 km, the MinXSS-1 mission life is only about 6 months. The MinXSS-2 spacecraft was built in parallel with MinXSS-1 and is being delivered to Spaceflight Industries in fall 2016 for its launch into a 500-km sun-synchronous orbit (SSO). This free ride-of-opportunity for MinXSS-2 from Google Terra Bella (formerly Skybox Imaging) was not planned in the original MinXSS program that only provides support for development of the MinXSS spacecraft and the MinXSS-1 mission through 2016. This proposal supports the new MinXSS-2 mission for two years (2017-2018) and an extended mission for two more years (or opportunity to be extended in the next Senior Review in 2017). As with MinXSS-1, closure on the science objectives involves comparisons with SDO and RHESSI measurements, ITM modeling using the NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM), and improvements to the empirical Flare Irradiance Spectral Model (FISM) that is used for a variety of space weather research applications. New for MinXSS-2 is the addition of comparative studies with Hinode and NuSTAR solar measurements, studies correlating the measured photospheric magnetic field flux to soft X-ray spectra, and physics-based modeling of the SXR spectra. We have added two more Co-Is for supporting the extra research, and we are also adding a second ground station at Geophysical Institute (GI) in Alaska for increasing the daily data downlink by a factor of six over MinXSS-1. We are willing to share LASP and GI ground stations with another NASA CubeSat.