The European Space Agency (ESA) Arrakihs space mission has passed the Instrument Preliminary Requirements Review (iPRR) in just six months, a key step for the space agency to approve advancing the phase with the aim of completing the mission’s Payload. This payload is the brain of Arrakihs, an instrument composed of two visible cameras and two infrared cameras that seek to obtain the deep images of the universe that will be necessary to achieve the scientific objectives of the mission, consequently, knowing the nature of the dark matter that makes up the cosmos.
This milestone took place last March, when the iPRR success led ESA to determine the transition from Phase A to Phase B, which will begin in May, and thus guarantee the continuation of what is called to be the next fast class mission in ESA's Science Programme (F2). The final decision on its adoption is expected in the first half of 2026.
The mission consortium, which includes more than 100 researchers from more than 20 research centres and universities in different countries, is led by the Institute of Physics of Cantabria (IFCA, CSIC-UC), a joint centre of the University of Cantabria and the Higher Council for Scientific Research, an agency dependent on the Ministry of Science, Innovation and Universities. “Arrakihs is a very beautiful mission, it is focused on a very specific objective, which is to try to demonstrate the nature of dark matter by obtaining very deep images, in the halos of galaxies like the Milky Way,” explains Rafael Guzmán, leader of the consortium and IFCA, CSIC-UC research professor.
ICE-CSIC and IEEC contribute in the three main areas of the mission: science, instrument and ground segment. Currently, ICE-CSIC, IEEC and SATLANTIS lead the main instrument of the Arrakihs payload, made up of an international consortium of European countries. In addition, it is expected that its facilities will serve to contribute to testing the fine guidance system (FGS) and the characterisation of the visible and infrared detectors that the instrument will equip. In the scientific field, the Cosmology research group contributes with unique cosmological simulations, in addition to participating in the ESA scientific study team.
The remnant of dark matter
The objective of the Arrakihs mission is to explore the Universe to understand the nature of the dark matter that comprises it. "To explain the structure and dynamics of our cosmos, it has been necessary to introduce a type of component that we cannot observe directly, but that gravitationally influences the movement of stars and galaxies," explains Guzmán. This is dark matter, which, according to the research community, constitutes more than 80% of the matter in the universe, and its effects can be revealed by the characteristics of stellar streams, faint traces of stars left by small galaxies orbiting in the halo of large galaxies like our Milky Way as they are destroyed by gravitational interaction.
Four high-precision cameras
To analyse these effects, Arrakihs will observe a representative sample of Milky Way-like galaxies in the local universe at very low levels of surface brightness, never achieved at visible and infrared wavelengths, using four high-precision cameras aboard a satellite that will orbit the Earth at around 800 km altitude.
"The successful completion of the iPRR marks a pivotal moment for Arrakihs," said Santiago Serrano, the instrumentation team lead (Satlantis and Institut d’Estudis Espacials de Catalunya, IEEC). "Our team has demonstrated remarkable technical expertise and dedication to advancing the mission at an extraordinary stage. We are excited to move the instrument payload forward to Phase B."
This milestone has been a crucial step for the development of the mission which, in the words of Stefan Kögl, project manager of the iPRR, “means that we are prepared for the most detailed and expensive phases of development, increasing the probability that the entire mission will be a success.” For his part, Patricio Vielva, IFCA director, highlights that the move to Phase B is key “to demonstrate the viability of the critical instrumentation for the mission, and crucial towards the adoption of the mission by ESA.”
Next steps towards 2030
The Arrakihs team will now work for two years to achieve the goal of successfully completing Phase B with the approval of the Instrument Preliminary Design Review (iPDR) in the first half of 2026. This will be the last of different steps in the decision for Arrakihs to be adopted as the next fast-class mission in the ESA's Scientific Program (F2), with an estimated launch date of 2030.
This is the next objective of the mission consortium, led by Spain, with important contributions from Switzerland, Belgium, Sweden, Austria, the United Kingdom and Portugal, and with additional contributions from the Netherlands, Norway, the United States, Taiwan and Thailand. In addition, the consortium includes companies from the aerospace sector, led by the Spanish company Satlantis, and contributions from scientists from different institutions, such as the Institute of Space Sciences (ICE-CSIC), the Complutense University of Madrid (UCM), the Center for Physics Studies of the Cosmos of Aragon (CEFCA), the Institut d'Estudis Espacials de Catalunya (IEEC), the Institute of Astrophysics of Andalusia (IAA-CSIC) and the National Institute of Aerospace Technology (INTA).
“The origin of Arrakihs is in Spain. It was born as an idea from a group of Spanish astrophysicists; but we were aware that a project of this magnitude could not be carried out without the participation of more groups and more countries. The enthusiasm and involvement of all of us who work for Arrakihs in Spain is magnificent, and that makes the coordination and management of these groups easy," concludes María Ángeles Gómez-Flechoso (UCM), coordinator of the Spanish nodes and responsible for the Arrakihs Survey Strategy.
