HaloSat was designed to survey the distribution of hot gas in the Milky Way and constrain the mass and geometry of the Galactic halo.

The mission, led by the University of Iowa (UIowa, PI P.Kaaret) as a rapid-development CubeSat mission, was selected by NASA with funding started in 2016. Launched on May 21, 2018 from the Wallops Space Flight Facility, as part of the payload of the Cygnus OA-9 International Space Station (ISS) resupply mission, HaloSat was placed in the airlock of the Japanese Experiment Module (JEM) and deployed into circular low Earth orbit on July 13, 2018 using a Nanoracks CubeSat Deployer. The science operations started in October 2018.

To trace the Galactic halo, HaloSat is equipped with a non-focusing instrument, comprised of three independent silicon drift detectors with the following characteristics:
  • Energy range : 0.4–7.0 keV
  • Field of view : 10 deg diameter full response, tapering to 14 deg zero response
  • Energy Resolution : ~85 eV at 677 eV and ~137 eV at 5895 eV.
The observing strategy was to divide the sky into 334 positions and acquire a minimum of 8000 detector-seconds for each position. Originally approved for 12 months of science operations, HaloSat successfully collected science data from October 15, 2018, up to September 29, 2020, effectively doubling the mission life time. HaloSat was the first mission dedicated to Astrophysical Science using a Cubesat platform.

The science data center is located at UIowa where the data are processed and the outputs provided to the HEASARC archive for public distribution. Mission operations are handled by Blue Canyon Technologies.

Latest News

May 23, 2023

The catalog with the fitting results of the HaloSat Circumgalactic Medium (CGM) fields is now available in the archive.

May 1, 2023

All Halosat data collected during the science operations from Oct 15, 2018 and Sep 29, 2020 were reprocessed (version hsuf_20221026) and are now available from the HEASARC archive. More details are available in the reprocessing page

Dec 14 2022

Release of a report on the Halosat background and an update of the data analysis guide

Feb 14, 2022

Release of a report on the in-flight calibration and an update of the data analysis guide

Feb 12, 2021

The complete HaloSat data archive is now available from the HEASARC. This release includes all data collected during the science operations from Oct 15, 2018 and Sep 29, 2020. The observations include 415 fields covering all the sky.

Jan 4, 2021.

HaloSat reentered Earth's atmosphere on January 4, 2021 marking the end of the satellites nearly two and a half year orbit. More on HaloSat

Apr 15, 2020.

HaloSat archive opens