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ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) is an ESA astronomy mission for imaging faint galaxies in the nearby Universe to provide important measurements to test open questions in cosmology.

ARRAKIHS will use innovative twin binocular assemblies of small telescopes to image about a hundred nearby galaxies and their surroundings in order to characterize the number and nature of low-mass dwarf galaxies and stellar streams in their vicinity. This survey in visible and infrared wavelengths will far exceed what is currently possible with ground-based telescopes, allowing for tests of so-called ΛCDM cosmology as well as the production of a dataset of significant legacy value.

The mission will image 50 square degrees of the sky per year in two visible bands (380 to 630 nm and 550 to 900 nm) and two infrared bands at unprecedented ultra-low surface brightness (SB) (920 to 1230 nm and 1169 to 1590 nm). These images will allow us to address major unresolved issues in the cosmological model of Λ-Cold Dark Matter (ΛCDM). If Dark Matter in our Universe deviates from the cold and collisionless model of the standard ΛCDM, then satellite mass functions, satellite merger rates, and the prevalence of stellar streams around dwarf galaxies are all expected to be greatly suppressed. These observational tests could not yet be performed because imaging down to ultra-low SB limits from the ground is extremely difficult due to atmospheric background. ARRAKIHS will instead use an innovative binocular telescope assembly mounted on a mini satellite in Low Earth Orbit. This survey will yield a first-of-its-kind catalog of ultra-low SB extragalactic images for a volume-limited and mass-limited sample of nearby universe galaxies like the Milky Way. The ARRAKIHS mission will image these systems down to an unprecedented surface brightness of 31 mag/arcsecond2 with a resolution of 0.8 arcsec (FWHM) in visible wavelengths and 30 mag/arcsecond2 with 1.25 arcsec (FWHM) in near-infrared wavelengths.

ARRAKIHS is scheduled for launch in the early 2030s on a Vega-C or as a ride-share mission.

Nation: Europe
Type / Application: Science, astronomy
Operator: ESA
Contractors: Airbus Defence and Space
Power: Solar cells, batteries
Mass: < 300 kg
Orbit: 600 - 1000 km SSO
Satellite COSPAR Date LS Launch Vehicle Remarks
ARRAKIHS - 203x Ko ELV Vega-C (baselined)

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