CARIOQA Phase B - The next step on the European path to quantum sensors in space

CARIOQA (Cold Atom Rubidium Interferometer in Orbit for Quantum) is a European initiative to demonstrate quantum sensing from space, paving the way for next-generation, gravimetry-based climate and Earth-system observations. By deploying a cold atom interferometer on a dedicated satellite, CARIOQA seeks to validate the operational feasibility of quantum sensors in a space environment, thereby strengthening Europe’s technological sovereignty in quantum technologies and pushing the boundaries of space-based science.The first part of CARIOQA – the Pathfinder Mission Preparation (PMP) – started in late 2022. It focuses on the development of an engineering model of the quantum accelerometer accompanied by the scientific background and considerations for the operation in orbit. Phase A (PHA), executed from early 2024 to mid-2025, defined the mission architecture, established requirements on the mission, instrument and satellite, and successfully demonstrated the technical feasibility of a Quantum Space Gravimetry Pathfinder Mission within the next decade. Building on this progress, Phase B (PHB) officially began in October 2025 and will span 24 months. During this phase, the mission concept will be consolidated, and critical technologies for both the quantum payload and satellite platform will be advanced to Technology Readiness Level (TRL) 6. This milestone will validate the maturity and space worthiness of key components, positioning CARIOQA for future flight implementation.While the primary objective of CARIOQA is the technological demonstration of a spaceborne quantum accelerometer, the mission also addresses scientific questions. These include the potential of quantum sensors to achieve higher accuracy in Earth’s gravity field recovery, probe the density of the upper layers of the atmosphere and the feasibility of upgrading the accelerometer into a spaceborne gradiometer. Such capabilities could revolutionise the ability to monitor mass transport processes—such as the distribution of water masses—offering vital data for climate change modelling, sea-level rise assessment, and sustainable water resource management.This contribution presents the current status and scientific vision of CARIOQA-PHB, highlighting the scientific possibilities of a quantum pathfinder mission.CARIOQA-PHB is a joint European project, funded by the European Union (id: 101189541), including experts in satellite instrument development (TAS, exail, ZARM, LEONARDO), quantum sensing (LUH, LTE, LP2N, ONERA, FORTH), space geodesy, Earth sciences and users of gravity field data (LUH, TUM, POLIMI), mission analysis (GMV) as well as in impact maximisation and assessment (PRAXI Network/FORTH, G.A.C. Group), coordinated by the French and German space agencies CNES and DLR under CNES lead.