Tianwen-4

• 1. Origins And Naming

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  The mission carries the name Tianwen-4, a title that signals its place in China's expanding interplanetary fleet. Before adopting this designation, planners referred to it as Gan De. This earlier name honored an astronomer from the fourth century BCE who made early planetary observations. Some historical accounts suggest he first observed the Galilean moons with the unaided eye. The choice of name reflects a strategic desire to build upon centuries of Chinese astronomical tradition while launching into modern space exploration. In 2018, Pei Zhaoyu served as deputy director of CNSA's Lunar Exploration and Space Program Center. He stated that China planned four major interplanetary missions before the end of the 2020s. These included Tianwen-1 for Mars, Tianwen-2 for asteroid sample return, Tianwen-3 for Mars sample return, and the Jupiter system mission now known as Tianwen-4. The agency had already launched Chang'e 1 and Chang'e 2 robotic lunar orbiters. They followed these with Chang'e 3, which landed on the Moon. By the 15th of October 2003, China had successfully sent its first independent crewed orbital mission into space. These achievements formed the foundation for more ambitious projects beginning in the 2020s.

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• 2. Competing Mission Profiles

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  Western media reports describe two competing mission profiles under consideration: the Jupiter Callisto Orbiter and the Jupiter System Observer. The Jupiter Callisto Orbiter would conduct flybys of Jupiter's irregular satellites before entering a polar orbit around Callisto. This profile may include a lander or impact probe to study the moon's surface directly. In contrast, the Jupiter System Observer would forgo an attempt to orbit Callisto. Instead it focuses on intensive studies of Io, Jupiter's volcanic moon. The spacecraft would perform several flybys to examine how Jupiter's gravity powers Io's eruptions. It might also release small satellites to study the dynamics of the Jovian magnetosphere from multiple points. At the end of its tour, this profile could send the craft to the Sun, Jupiter L1 point. There the planet's gravity balances with the Sun's allowing long-term observation of solar wind outside Jupiter's magnetic field. Presentations by Chinese researchers suggest that the Jupiter Callisto Orbiter combined with a Uranus flyby probe may have been selected by mission planners during 2023 and 2024. Reports published in China Space Science and Technology support this direction as of early 2024.

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• 3. Trajectory And Timeline

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  One possible Earth, Jupiter mission trajectory was presented at the 2020 General Assembly meetings of the European Geosciences Union. Under this scenario the Tianwen-4 probe launches in September 2029. Six months later in April 2030 it conducts a Venus fly-by. The spacecraft then encounters Earth twice: first in February 2031 and again in May 2033. Before arriving at Jupiter the sub-probe separates from the main probe. It continues toward Uranus for a flyby scheduled in March 2045. The main probe enters Jupiter orbit in December 2035. After one or two braking passes it stays in a large elliptical orbit around Jupiter with a period of 30 days. During about a year it completes ten orbits while making flybys of irregular moons. In February 2038 Tianwen-4 enters orbit around Callisto at an altitude of 300 km. Its orbital period becomes 17.7 hours. An impact probe releases to strike the surface of Callisto shortly after arrival. This timeline reflects careful planning to use gravity assists and minimize fuel consumption over decades.

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• 4. Scientific Payloads And Instruments

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  Potential scientific instruments were discussed during a session of the 2020 General Assembly of the European Geosciences Union held in May 2020. Four payload packages address the mission's main goals regarding formation and current workings of the Jovian system. Package A includes plasma and dust analyzers such as a thermal plasma spectrometer operating between 100 eV and 100 keV. It also contains high-energy charged particle detectors and energetic neutral atom analyzers. Package B features multi-wavelength imaging and spectroscopy tools including visible-wavelength cameras and near-infrared imagers. Far-infrared submillimeter wave radiometers and ultra-violet imagers complete this suite. Package C holds geology glaciology and geochemistry analyzers like high-mass resolution mass spectrometers fed by sampling systems for ice surfaces. Package D covers radio optical links and radio science instruments including transmission reception radio links for Doppler tracking. The 2024 update published in China Space Science and Technology lists specific instruments for the Jupiter Callisto Orbiter. These include microwave radiometers atmosphere composition monitors polarimeters cameras spectrometers particle analyzers magnetometers microwave radars gamma X-ray spectrometers. An interplanetary flyby probe carries its own camera magnetometer spectrometer radio science package and particle analyzer.

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• 5. Callisto Landing Strategy

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  The outermost of the four Galilean moons is Callisto. Its interior experiences less heating due to gravity from other moons and Jupiter itself. It likely formed with leftover Jupiter material and has sat mostly dormant since then. Only asteroid impacts have modified its surface over billions of years. This makes it a prime target for studying early Solar System history. A lander on Callisto would provide unprecedented insights into the moon's formation and evolution. The moon possesses a thin atmosphere containing small amounts of oxygen adding scientific allure despite being less glamorous than Europa or Ganymede. It also sits outside Jupiter's intense radiation field making landing technically easier than on other Jovian moons. A spacecraft requires less fuel to reach Callisto compared to closer satellites. These rationales argue strongly for Callisto as the main mission target within the Jupiter Callisto Orbiter profile. An impact probe releases to strike the surface after orbital insertion in February 2038 at an altitude of 300 km.

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• 6. Uranus Flyby Component

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  Presentations by Chinese researchers suggest that Tianwen-4 may include an additional probe conducting a fly-by of Uranus sometime after 2040. Under the selected Jupiter Callisto Orbiter plus Uranus flyby profile this secondary craft travels independently toward the ice giant. It separates from the main probe before reaching Jupiter and continues its journey alone. Scheduled encounters place the Uranus flyby in March 2045 according to one trajectory scenario. The interplanetary flyby probe carries its own camera magnetometer spectrometer radio science package and particle analyzer. This component allows simultaneous exploration of two major outer planets using a single launch architecture. Reports published in China Space Science and Technology indicate this combined approach may have been chosen by mission planners during 2023 and 2024. The dual-target strategy maximizes scientific return while minimizing overall cost and complexity across decades of travel time.

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