ARRAKIHS

ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) is a planned European Space Agency (ESA) space mission designed to study dark matter and galaxy formation by observing low-surface-brightness structures in the halos of nearby galaxies. Selected in November 2022 as an ESA F-class mission,^[1] ARRAKIHS is currently in its definition phase, with a projected launch in 2030.

ARRAKIHS

Mission type	Cosmology, Dark Matter
Operator	ESA
Website	https://www.arrakihs-mission.eu/
Mission duration	3 years (nominal)
Spacecraft properties
Manufacturer	Satlantis (Instrument) AVS and Redwire (platform primes to PDR)
Landing mass	600 kg
Payload mass	160 kg
Dimensions	~1.5 x 1.5 x 1.6 m3
Start of mission
Launch date	Expected 2030
Main telescope
Type	2 x iSIM170 camera
Focal length	1500 mm (f/10.15)
Wavelengths	280-900 nm visible 900-1600 nm near infrared

The mission aims to test the Λ-Cold Dark Matter (ΛCDM) model by analysing discrepancies between theoretical predictions and observations of small-scale structures, such as tidal stellar streams and dwarf satellite galaxies.

To achieve this, ARRAKIHS will observe the local universe at very low surface brightness levels never before reached in visible and infrared wavelengths, using an innovative binocular telescope system designed specifically to capture ultra-low surface brightness images. The instrument will be launched on a mini-satellite that will orbit the Earth at an altitude of 800 km.^[2]

Name

The mission is named after the planet Arrakis from science fiction novel Dune. The name is a backronym of "Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys".

Background and objectives

ARRAKIHS was proposed by an international consortium of scientists to address the reported tensions between the ΛCDM model, baryonic physics (BP), and ground-based observations of small-scale structures (satellites and stellar streams) in the Local Universe. The mission objective is to compare three key halo properties with current models: the identification and measurement of tidal stellar structures in halos, the structure and luminosity profiles of galaxy stellar halos, and the mass functions of dwarf galaxy satellites. Many of these dwarf galaxies are expected to show signs of disruption, forming diffuse tidal structures as they are accreted by their host galaxy. These structures will contribute to intra-halo light, creating first stellar streams and then, after total disruption, contributing to the faint, extended halo around galaxies.

The mission will offer a statistically significant sample of observables to evaluate whether discrepancies in the ΛCDM model are caused by selection biases or small sample sizes. If these tensions are confirmed, the mission will highlight inconsistencies in current galaxy formation models and may necessitate revisions or the exploration of alternative frameworks to explain the observed data more accurately.^[2][3]

Survey and mission profile

ARRAKIHS is planned to conduct a three-year survey, imaging roughly 100 square degrees of the sky observing approximately 75 Milky Way-type galaxy halos.

Calibration mode

The ARRAKIHS mission will have three operation modes: survey mode, where it will observe the sample galaxies for the ARRAKIHS science goals and the calibration mode.

Survey mode: Each of these targets will be observed simultaneously in 4 bands for a total of 150h, with 900 exposures of 10 minutes each at different times.

Calibration mode: 7% of the observing time will be scheduled for calibration tasks including bias and pseudo-dark exposures, observation of flat-fielding correction, astrometric and photometric calibration, routine monitoring of the PSF and detector pixel operability,

Instrument

The ARRAKIHS mission's primary payload is a dual binocular telescope system with a modified Maksutov Cassegrain design equipped with two visible-wavelength and two infrared cameras, optimized for low surface brightness astronomy. Developed by the Spanish aerospace company Satlantis, the prime contractor for the instrument's design and manufacturing, the system is designed to detect extremely faint stellar structures surrounding galaxies with high sensitivity and precision.^[4][5][6]

Telescope design

The binocular telescope system features:

ARRAKIHS payload design

• Telescope & Camera Module: Includes opto-mechanical assemblies, straylight baffles, instrument structure, focal plane assemblies with Visible CMOS sensors and H2RG detectors, and passive/active thermal control. Also includes the Straylight Baffle Assembly that rejects light outside the field of view such as bright stars and earth shine. =

• Electronics Box: Houses control and data processing units, thermal regulation systems, and power distribution.

Filters

• VIS filters, operating at visible wavelengths (VIS1: 280-420nm , VIS2: 381-863 nm), 2x Te2v CIS304 detectors.
• NIR filters, operating at near-infrared wavelengths (NIR 1: 857-1255nm , NIR2: 1168-1567 nm), 2x Teledyne H2RG detectors.

Satellite and instrument operations

The telescope will be integrated into a small satellite platform with a total mass of approximately 600 kg. Operating in a sun-synchronous low Earth orbit (LEO) at an altitude of 800 km, for which the spacecraft is designed with specialized baffling and thermal control systems to minimize stray light and thermal noise, ensuring stable observational conditions.^[2][4]

The ground segment of a space mission encompasses all Earth-based infrastructure required for spacecraft operations, data reception, processing, archiving, and distribution. It consists of several key components, including ground stations that facilitate communication with the spacecraft and a mission control center responsible for its management.

In the case of the ARRAKIHS mission, the ground segment also includes the computational infrastructure necessary to process raw data, specialized software for generating and archiving scientific images, and calibration tools to periodically adjust the onboard instruments. These elements ensure the mission's efficient operation and data dissemination.  The responsaibility of the structural and scientific components of the ARRAKIHS Ground Segment is distributed between ESA and the ARRAKIHS Mission Consortium.

The Science Ground Segment (SGS) is managed by ESA and includes ESA tracking facilities, the Mission Operation Center (MOC), the Science Operations Center (SOC), and the long-term archive of the mission:

• The MOC is responsible for operating the ARRAKIHS spacecraft, ensuring its safety and health, managing orbit and attitude control, handling all telemetry and telecommand processes, coordinating ground station access, and serving as the central hub for real-time operations, including anomaly resolution and commissioning activities.
• The SOC is responsible for planning and executing the scientific operations of the mission, generating observation schedules and instrument commands, processing and validating science data up to Level 1, managing the science archive, supporting the scientific community, and coordinating with the Instrument Operations and Science Data Center (IOSDC) for calibration, higher-level data products, and instrument monitoring.
• The long-term archive will store the data and will make it publicly available, using Visual Observatory standards within the ESA Sky framework.

The Instrument operations and Science Data Center (IOSDC) is responsaibility of the ARRAKIHS Mission Consortium and manages four key aspects of the mission:

• Mission planning: produces the long- and short-term planning of observations and the optimized Concept of Operations (CONOPS). The responsibility of this task is shared with ESA.
• Instrument operation: produces the protocol for monitoring the operation of the payload as well as the calibration sequence.
• Data reduction: develops the data reduction pipeline to produce all the data product levels.
• Science Data Center: Manages the ARRAKIHS data archive and regular execution of the reduction developed in the data reduction stage. The Science Data Center is located at the Instituto de Física de Cantabria (IFCA, CSIC-UC).

ARRAKIHS Mission Consortium 

The ARRAKIHS Mission Consortium (AMC) is a collaborative network of scientists, engineers, and technical experts from leading research institutes and companies across Europe and beyond. It includes members from Spain, Austria, Belgium, Sweden, Switzerland, Norway, Portugal, and the United Kingdom, which are collectively responsible for funding, designing, and operating the mission's scientific and instrumental components. The consortium also collaborates with research institutions from the Netherlands, France, Denmark, the United States, Thailand, and Taiwan. The Spanish company Satlantis serves as the prime contractor for the instrument, leading a group of technological firms across Europe.

The AMC is organized into three key operational area: Instrumentation, Science, and the Instrument and Science Data Operations Center (IOSDC). Each of which is structured into specialized work packages to ensure the mission's success.^[4]

Milestones

ARRAKIHS is an F-class mission of the European Space Agency (ESA), selected on 2 November 2022 with participation from institutions of five european member states (Spain, Switzerland, Austria, Belgium and Sweden). Following its selection, the ARRAKIHS consortium expanded, holding its kick-off meeting in Barcelona in July 2023 with representatives from over 15 institutions across the member state and collaborators countries.

In early 2024, the mission completed its Payload Preliminary Requirements Review (iPRR), concluding Phase A of development.^[7] By the end of that year, the ARRAKIHS Mission Consortium (AMC) had grown to include more than 150 researchers and engineers from more than 40 institutions of different countries and with the confirmation of three more state members (Portugal, Norway and United Kingdom).

Pending successful Instrument and Spacecraft Preliminary Design Reviews (iPDR and SC PDR), the mission is expected to achieve adoption by mid-2026. Its launch is scheduled for late 2030.

ARRAKIHS workflow

Complementarity with Euclid data

ARRAKIHS observations will be complemented by higher-resolution data from Euclid, which will map the same galaxies as part of its Wide Field Survey. The potential synergies between the two missions were studied under an International Space Science Institute (ISSI) project titled "The Extremely Low Surface Brightness Universe: Calling for Synergy between the ESA Euclid and ARRAKIHS Space Missions" [8]

See also

• List of European Space Agency programmes and missions