Quick Facts: Miniature X-ray Solar Spectrometer (MinXSS)

Mission Introduction

Three MinXSS units, a prototype and two flight models, have been fabricated at LASP. The prototype has been valuable for early testing, fit checks, and for developing flight software. FM-1 deployed from the International Space Station in May 2016 and FM-2 is planned to launch with Google Skybox in late 2017. (Courtesy LASP)

Three MinXSS units, a prototype and two flight models, have been fabricated at LASP. The prototype has been valuable for early testing, fit checks, and for developing flight software. FM-1 deployed from the International Space Station in May 2016 and FM-2 is planned to launch on Spaceflight’s SSO-A rideshare mission in the fall of 2018. (Courtesy LASP)

The Miniature X-ray Solar Spectrometer (MinXSS) was a four-year, student-led project to design, build, integrate, test, and operate a three-unit (34x10x10cm) CubeSat. The first MinXSS flight model successfully launched to the International Space Station on December 6, 2015 to take observations of the sun. Deployment from the ISS occurred on May 16, 2016 and after nearly one year of science operations, the first MinXSS flight model burned up in Earth’s atmosphere as planned on May 6, 2017. Over 40 University of Colorado Boulder students contributed to the project with professional mentorship and technical contributions from professors in the Aerospace Engineering Sciences Department at CU and from LASP scientists and engineers. The second MinXSS flight model (MinXSS-2) is scheduled to launch on November 19, 2018.

The science objective of the first MinXSS mission was to better understand the solar irradiance energy distribution of solar flare soft x-ray (SXR) emission and its impact on Earth’s ionosphere, thermosphere, and mesosphere (ITM). Energy from SXR radiation is deposited mostly in the ionospheric E-region, from approximately 80 to 150 km, but the altitude is strongly dependent on the SXR spectrum because of the steep slope and structure of the photoionization cross sections of atmospheric gases in this wavelength range. This region is of particular interest for observations of solar variability due to flares and the evolution of active solar regions.

MinXSS data helped to improve our understanding of the physics of solar flares themselves. The energy range observed by MinXSS is rich with high-temperature spectral lines from coronal plasma with temperatures from 5 to 50 million K, which are greatly enhanced during even small solar flares. MinXSS observed a continuum of energy ranges that provide an independent diagnostic of the emitting plasma temperatures. Understanding how solar flares heat plasma, especially up to many tens of million K, is a pressing question in solar physics and the MinXSS observations provided the best spectral measurements in this energy range to date. Observing the variations of spectral lines in comparison to the continuum also provided insight into coronal elemental abundances, particularly for Mg, Si, Fe, S, and Ar, to help measure abundances and to understand how they may vary with solar activity and during flares.

MinXSS-2 improves upon several aspects of MinXSS-1:

  • The primary science instrument, an Amptek X123 silicon drift detector, has been upgraded with higher energy resolution and greater dynamic range. MinXSS-2 will be able to resolve spectral lines better and can observe larger solar flares without saturating the detector.
  • The flight radio can transmit at 19200 bps in addition to the default 9600 bps, which will enable downlinking more data than MinXSS-1 was capable of. An additional ground station in Fairbanks, Alaska, will allow yet more data to be downlinked.
  • MinXSS-2 can store commands onboard that will be executed at particular times and can be downlinked over any other ground station with which we have coordinated.
  • MinXSS-2 will be placed into a Sun-synchronous orbit at 575km altitude. This high latitude orbit means MinXSS-2 will be very well aligned with our ground station in Alaska and will get more long duration passes each day there. The higher altitude means that there will be less drag and the satellite can stay up longer. We’re expecting to operate MinXSS-2 for about 5 years, compared with just 1 for MinXSS-1.

With a 5-year mission, MinXSS-2 will observe a significant portion of the 11-year solar cycle. MinXSS-2 science questions:

  • How do soft X-ray (SXR) flare energetics change with different size active regions/magnetic complexity over the solar cycle?
  • What are the differences in Earth’s ionosphere and thermosphere responses to the solar SXR radiation during different solar cycle phases?
  • Do the coronal heating processes, plasma temperature, and composition change for active regions during the different solar cycle phases?

Project Contributors

  • Principal Investigator, Tom Woods, LASP Associate Director for Technical Divisions
  • Co-investigators Amir Caspi (Southwest Research Institute), Phil Chamberlin (NASA Goddard), Andrew Jones (LASP), Rick Kohnert (LASP), Xinlin Li (LASP and CU Aerospace Engineering Sciences, AES), Scott Palo (CU/AES), and Stan Solomon (NCAR High Altitude Observatory, HAO)
  • More than 40 students from different majors including astronomy and planetary sciences, aerospace, mechanical, electrical, and computer engineering helped to design the mission and build all of its subsystems. The lead student throughout the project was James Mason, CU/AES and LASP
  • AES provided the CubeSat laboratory, machine shop, and teaching faculty for the project (Professors Scott Palo and Xinlin Li)
  • LASP assisted with fabrication and flight software development, and provided instrument testing facilities and equipment, as well as scientific and technical mentorship for the project

For more information about MinXSS and MinXSS-2, see:

Scientific Instruments

For the MinXSS spectrometer, the enabling technology providing the advanced solar SXR spectral measurements was the Amptek X123-SDD, a commercial-off-the-shelf silicon drift detector (SDD). The Amptek X123 has a low mass (~324 g after custom modification), modest power consumption (~2.5 W), and small volume (2.7” x 3.9” x 1.0”), making it ideal for a CubeSat. MinXSS included two secondary instruments, a Solar Position Sensor (SPS) and an X-ray Photometer (XP), which provided support for scientific analysis of data from the X123-SDD. The SPS was a quad-diode, responsible for calculating the sun’s position and relaying this information for inclusion in the fine-attitude control solution and for use in science processing. The XP was a single diode that provided a measurement that was compared to the integrated X123 spectrum and was used in science data processing.

Quick Facts

Launch date: MinXSS: December 6, 2015 (deployed from ISS on May 16, 2016 and reentered the atmosphere on May 6, 2017); MinXSS-2: December 3, 2018
Launch location: Cape Canaveral, Florida (MinXSS); Vandenberg Air Force Base, California (MinXXS-2)
Launch vehicle: Atlas V (MinXSS); SpaceX Falcon 9 (MinXSS-2)
Mission target: Low Earth orbit
Mission duration: Minimum three months of science operations
Key organizations involved:

  • University of Colorado Boulder (CU)
  • NASA Goddard Space Flight Center (GSFC)
  • National Science Foundation (NSF)
  • National Center for Atmospheric Research (NCAR)
  • Southwest Research Institute (SwRI)
  • NIST Synchrotron Ultraviolet Radiation Facility (SURF)
  • Spaceflight Industries