The Idefix rover, developed jointly by the German Aerospace Center (DLR) and the French space agency CNES, has begun its journey to Mars' moon Phobos following the launch of Japan's Martian Moons eXploration (MMX) spacecraft on October 19, 2026. The 25 kg rover incorporates a lightweight structural system built around carbon-fibre-reinforced polymer (CFRP) composites and aluminium honeycomb sandwich panels. It is scheduled to reach Phobos around the turn of 2028 and 2029, where it will investigate the moon's surface for approximately 100 days.
CFRP Sandwich Construction Reduces Structural Mass
The rover's chassis weighs just 2.96 kg and consists of more than 160 bonded components. As JEC Composites reports, its main panels use a sandwich construction, with two outer CFRP skins separated by an aluminium honeycomb core. This configuration provides high stiffness at low mass, an important requirement for a compact rover that must withstand rocket-launch vibrations, landing impacts and the mechanical demands of operating in extremely low gravity.
The chassis also incorporates carbon-fibre-reinforced PEEK (CF-PEEK) inserts at locations exposed to concentrated loads. These inserts replace portions of the honeycomb core and provide attachment points for components such as the wheel units. Additional CFRP stiffening ribs distribute loads from these attachment points into the surrounding sandwich panels, while titanium flanges provide further load-transfer and mounting interfaces.
The material combination is designed to balance lightweight construction with local strength. Rather than relying on a uniformly thick structure, the design uses composite skins for stiffness, a honeycomb core for efficient structural support, and reinforced inserts where bolted connections and concentrated forces require additional reinforcement.
Composite Structures Engineered for Extreme Conditions
Thermal stability is another key design consideration. Phobos experiences temperature variations exceeding 200°C over its day-night cycle. The rover's cover plate, which supports the solar generator and associated electronics, must remain dimensionally stable between approximately -145°C and +75°C. Despite these requirements, the plate weighs only 324 grams and carries equipment accounting for approximately 16% of the rover's total mass.
The rover's mechanical-electrical-communication and separation system (MECSS) also uses a sandwich structure, incorporating a 40 mm-thick aluminium honeycomb core to achieve high bending stiffness during launch. Its integrated release mechanism will detach the rover from the MMX spacecraft before the descent to Phobos. A spring-driven push-off system will propel the rover away from the mothercraft at approximately 20 cm per second.
These structural features support a mission in which the rover will be released from a height of approximately 40 to 100 metres, experience an uncontrolled impact and potentially several rebounds, then autonomously right itself and deploy its solar panels. Phobos has less than one-thousandth of Earth's gravity, making landing and wheeled movement in this environment a major engineering challenge.
Rover to Investigate Phobos Ahead of Sample Return
After reaching Mars, the MMX spacecraft will study Phobos and Deimos from orbit before deploying Idefix on Phobos. The rover will analyse surface properties using two DLR instruments: the RAX Raman spectrometer and the miniRAD radiometer. Its measurements will help characterise the moon's mineralogical, mechanical and thermal properties and support selection of a landing site for the spacecraft's later sampling operation.
The broader MMX mission, led by the Japan Aerospace Exploration Agency (JAXA), aims to collect samples from Phobos and return them to Earth in 2031. Idefix builds on the German-French team's experience with MASCOT, a lander deployed to asteroid Ryugu during Japan's Hayabusa2 mission in 2018. Unlike MASCOT, which moved by hopping, Idefix is designed to travel across the surface on wheels.
The rover demonstrates how CFRP sandwich panels, honeycomb cores, reinforced polymer inserts and metallic interfaces can be combined to meet demanding spaceflight requirements. Its mission will also provide operational experience with lightweight composite structures exposed to launch loads, extreme temperature variations and the low-gravity environment of a small celestial body.
