The China National Space Administration opened a scientific-payload competition for Tianwen-4 on November 13, 2026, inviting proposals for a mission intended to orbit Jupiter and conduct orbital and landing exploration of Callisto. The agency’s international opportunity announcement describes an orbiter carrying 10 scientific instruments and a lander carrying two.
The planned instruments combine remote observations with measurements of particles, magnetic fields, and surface material. The orbiter’s proposed equipment includes cameras, spectrometers, and a Callisto laser altimeter. The lander’s two designated payloads are a surface-composition analyzer and a magnetometer.
Instruments for an Icy Moon
Callisto is Jupiter’s second-largest moon and the third-largest moon in the solar system. NASA’s Callisto overview describes a heavily cratered world whose surface preserves evidence of impacts. Observations by the Galileo spacecraft also indicated that a salty ocean may exist below its surface.
That combination gives surface measurements and orbital observations different scientific roles. Images record terrain and geological features over an extended area. Spectrometers examine how material interacts with radiation, helping distinguish composition. A laser altimeter measures distance to the surface to establish elevations along the spacecraft’s path.
A surface-composition instrument would examine material at the landing location. A magnetometer records the local magnetic field. Measurements from a landed instrument and an orbiting spacecraft sample different positions, linking local observations with the wider environment around the moon.
Galileo studied the Jupiter system from orbit until its mission ended in 2003. NASA also identifies observations of Callisto by Cassini and New Horizons. Tianwen-4’s stated landing objective would add a surface component to an investigation that also includes Jupiter orbit and Callisto orbit.
Proposals Due in December
The Chinese-language competition notice describes a competitive selection process assessing technical feasibility, costs, and the teams proposing each instrument. Domestic applicants must register for the requirements briefing by November 26. The proposal deadline is December 31, 2026.
International institutions may lead proposals or collaborate with Chinese-led teams. The international notice specifies Chinese and English PDF submissions and says that work undertaken by institutions outside the Chinese mainland generally requires their own funding.
The domestic rules limit a consortium to five participating organizations and require each member to account for at least 10% of the project budget. The notice places initial screening with the Lunar Exploration and Space Engineering Center, followed by an external assessment and a combined review of the leading proposals.
The immediate procurement step is the submission of instrument-development proposals. CNSA will communicate the international selection timetable separately.
