Japan’s MMX Spacecraft Ready for Phobos Sample Return Mission

The Japan Aerospace Exploration Agency (JAXA) has moved its Martian Moons eXploration (MMX) spacecraft to the Tanegashima spaceport, marking a critical step toward the first mission intended to return material from the Martian sphere to Earth.

The spacecraft arrived at the Tanegashima Space Center on March 31, 2026. Following its arrival, the vehicle was moved to the Spacecraft Test & Assembly Building 2 for unpacking and the commencement of launch site tests.

Launch Timeline and Technical Hurdles

JAXA expects to launch the MMX mission using the H3 rocket in either November or December 2026. This window is dictated by the optimal Mars launch window, which occurs every 26 months.

The mission has faced several delays, including an original scheduled launch in 2024 that was postponed due to technical issues with the H3 rocket. More recently, a second H3 failure occurred in December 2025. JAXA subsequently isolated the cause of that failure as a payload fairing separation anomaly, which allowed the MMX mission to proceed.

Mission Objectives and Flight Path

The MMX mission is designed to observe both of Mars’ moons, Phobos and Deimos, with a primary focus on Phobos. If the mission proceeds as planned, the spacecraft will enter orbit around Mars in 2027 to conduct mapping and analysis of the two moons and identify a suitable landing site.

In 2029, the spacecraft is scheduled to land on Phobos to collect approximately 10 grams (0.35 ounces) of samples. To facilitate this, the probe will enter a quasi-satellite orbit (QSO) around Phobos before descending to the surface.

Scientific Instrumentation and Research Goals

The spacecraft is equipped with 11 scientific mission instruments to study the topography, gravity, composition and internal structure of the Martian moons. The data gathered from these instruments and the returned rock and sand samples aim to resolve a long-standing debate regarding the origin of the Mars system.

Scientists are currently weighing two primary hypotheses for the formation of the moons:

• The giant impact hypothesis, which suggests the moons formed after a celestial body collided with Mars.
• The capture hypothesis, which proposes that the moons are asteroids from the outer Solar System captured by the gravity of Mars.

Beyond the origin of the moons, the mission seeks to clarify the evolutionary process of the Mars system and explore how habitable environments for life may have developed on terrestrial planets.

Technological Development and Collaboration

The MMX mission serves as a testbed for several critical deep-space technologies. JAXA aims to acquire advanced sampling technology for the surfaces of celestial bodies, optimal communication technology utilizing new ground-based probe stations, and the necessary capabilities for round-trip travel between Earth and the Mars system.

While led by JAXA, the mission is an international project featuring participation from several space agencies, including NASA, the European Space Agency (ESA), the German Aerospace Center (DLR), and the National Centre for Space Studies (CNES).