Tiangong Space Station

Modules: Tianhe, Wentian, and Mengtian

Tiangong's three-module architecture distributes functions logically across its structure. The Tianhe (天和, "Harmony of the Heavens") core module, launched on 29 April 2021, is the station's nerve centre. Weighing approximately 22,500 kg at launch and measuring 16.6 m in length with a maximum diameter of 4.2 m, Tianhe houses the primary life support, guidance, navigation and control systems, main propulsion, and the crew's primary living quarters. It is divided internally into three sections: living quarters with a galley, sanitary facilities, and workstations; a service module containing propulsion and thermal control hardware; and a docking hub with multiple ports for visiting crewed Shenzhou spacecraft and uncrewed Tianzhou cargo vehicles. Tianhe has two lateral berthing ports for the experiment modules, three axial docking ports for visiting vehicles, two large two-axis-steerable solar wings spanning over 55 m, and six lithium-ion battery sets. The module's total pressurized volume is about 113 m³, of which roughly 50 m³ is habitable.

Wentian (问天, "Quest for the Heavens"), the first experiment module, launched on 24 July 2022 and docked with Tianhe the same day. Like Tianhe, it has a maximum diameter of 4.2 m and an axial length of about 17.9 m. Wentian is oriented primarily toward space life sciences and biotechnology, housing a suite of life-science experiment racks, ecology science facilities, and backup attitude-control and life-support systems that enhance station resilience. It also carries a large robotic arm for external payload manipulation and support of spacewalks, two deployable external platforms offering 22 experiment sites for exposed payloads, and its own pair of solar wings with four battery sets.

Mengtian (梦天, "Dreaming of the Heavens"), the second experiment module, launched on 31 October 2022 and docked approximately 13 hours after launch. Sharing the same 4.2 m diameter and approximately 17.9 m length as Wentian, it forms the opposite arm of the T-shape. Mengtian is focused on microgravity science — fluid physics, combustion research, materials processing, and fundamental physics — and features 30 external experiment adapters. Its most distinctive feature is a dedicated cargo airlock that allows experiment hardware to be transferred between the pressurized interior and the exterior without a full spacewalk, substantially increasing the tempo of external experiment operations. Mengtian also carries its own solar wings and four battery sets.

Scientific Research and Experiments

Tiangong is designed as a genuine space laboratory, with CMSA having approved over 1,000 experiments to be conducted across the station's lifetime. The research programme is concentrated in five broad domains: space life sciences and bioastronautics; ecology and closed-loop life support; biotechnology and medicine; microgravity physics and materials science; and space technology demonstration. The two experiment modules divide this work thematically: Wentian is oriented toward life sciences and biology, while Mengtian focuses on physical sciences and microgravity engineering.

Biological and medical experiments have yielded some of the station's most significant early results. In the station's first operational years, Tiangong completed the first full rice life cycle in microgravity — from seed through growth to harvest and new seed — as well as Arabidopsis thaliana cultivation studies with implications for long-duration closed life-support systems. Zebrafish-based aquatic ecosystem experiments have been used to study nutrient circulation as a model for closed ecological systems needed on future deep-space voyages. Medical research covers bone loss mechanisms in microgravity, stem-cell behaviour, early mammalian embryonic development, and radiation-related effects relevant to cancer research, with recent missions returning 37.25 kg of samples from 25 experiments that included 20 different biological sample types.

Materials science experiments have explored tungsten alloys, high-strength steels, semiconductor crystal growth, novel lubricants, and materials reinforced with lunar regolith simulants. These address practical needs for next-generation jet engine turbine blades, deep-UV lithography equipment for semiconductor manufacturing, flexible space solar arrays, and long-lasting space lubricants. The microgravity environment aboard Tiangong removes the convective mixing and sedimentation that interfere with such materials processes on Earth, allowing more uniform crystal and alloy structures than are achievable terrestrially.

Among the most notable individual experiments conducted to date, the Shenzhou 19 crew performed 12 experiments using a drawer-type device employing semiconductor catalysts to convert carbon dioxide and water into oxygen and ethylene via artificial photosynthesis — the first in-orbit demonstration of this process. Producing both breathable oxygen and a hydrocarbon feedstock that could serve as rocket propellant precursor, the experiment demonstrated a key in-situ resource utilisation concept directly relevant to future crewed missions to the Moon and Mars.

Power System and Solar Arrays

Tiangong's electrical power system is one of the most capable ever deployed on a space station relative to its mass. The station's combined photovoltaic system is designed to generate over 100 kW of electrical power — roughly equivalent to generating around 1,000 kWh per day — sufficient to run all core systems and dozens of experiment racks with margin for expansion.

Each of the three modules carries one pair of large flexible solar wings. Wentian's arrays are the best-documented: each of its two wings is approximately 30 m long, giving a tip-to-tip wingspan of over 55 m and a collecting area of about 110 m² per wing. All six wings across the station use triple-junction gallium arsenide photovoltaic cells with a conversion efficiency exceeding 30%, substantially higher than the first-generation silicon arrays of the International Space Station. The wings are steerable around two axes, continuously tracking the sun to maximise power generation while managing aerodynamic drag and thermal cycling. This design also mitigates degradation from atomic oxygen, which is present in significant quantities at orbital altitudes.

Energy storage uses lithium-ion battery packs distributed across all modules: six sets in Tianhe, four in Wentian, and four in Mengtian. The batteries store power during the sunlit portion of each orbit to cover the approximately 35-minute eclipse periods that occur each 92-minute orbital revolution. Tianhe houses the main power management and distribution equipment, with cross-ties to the experiment modules allowing station-wide load sharing. The solar arrays are designed for up to 15 years of operational life, consistent with the station's overall design lifetime. Supporting this longevity, the Hall-effect thrusters used for orbit maintenance have been ground-tested for over 8,000 hours of continuous operation and consume roughly 90% less propellant than equivalent chemical thrusters, greatly reducing the refuelling demand on Tianzhou cargo missions.

Life Support Systems

Tiangong's environmental control and life support system (ECLSS) is housed primarily in the Tianhe core module and is regenerative — meaning it recycles water and other consumables rather than relying solely on resupply. China tested increasingly capable life support technologies on the earlier Tiangong-1 and Tiangong-2 space laboratories before fielding the operational system on the current station.

The system provides continuous pressure control, oxygen supply, carbon dioxide removal, trace contaminant control, and air circulation for a nominal crew of three. Water recovery includes urine recycling to produce potable water — an explicit feature of Tianhe's regenerative life support — along with humidity condensate collection. Solid waste is stored aboard and periodically disposed of via Tianzhou cargo vehicles, which deorbit and burn up in the atmosphere. Tianzhou missions also replenish food, gases, water top-ups, and replacement components for life support hardware, as well as propellant for the station's thrusters. The station's life support is sized for permanent three-person occupation over the intended decade-plus operational lifetime.

Future Expansion Plans

China has publicly confirmed plans to expand Tiangong beyond its current three-module T-shape. The first step is the addition of a fourth module — described in official and state-media statements as a multifunctional extension — that will attach to the Tianhe core module and transform the station from a T-shape into a cross-shaped four-module arrangement. This new hub module will feature multiple docking ports and a dedicated spacewalk airlock, and will serve as the primary attachment point for two further laboratory modules.

The ultimate goal is a six-module complex with a total mass of approximately 180–198 tonnes. China's Bai Linhou of the China Academy of Space Technology has explained the architecture: the current three-module station can expand to a four-module cross shape via the new hub, after which a second Tianhe-type core could enable attachment of two more modules. Hardware for this expansion is partly already in hand — China built a backup duplicate of the Tianhe core module in case of launch failure, and this unflown unit is reported to be available for reconfiguration as the new multifunctional module. Expansion missions are expected to use an upgraded Long March 5B with a larger payload fairing. No firm launch dates have been officially released for any of these expansion elements; official statements describe the work as planned for the "coming years."

Separately, the Xuntian (CSST) space telescope — a large co-orbiting optical telescope — is planned to launch around 2027 and will periodically dock with Tiangong for servicing and refuelling, extending its operational life while remaining independent of the station for most of its scientific operations.

Chinese officials have framed the expansion partly in the context of the anticipated retirement of the International Space Station around 2030–2031. A six-module Tiangong could serve as the primary long-duration crewed outpost in low Earth orbit for a period during and after the ISS transition, positioning China's space station as a key node for international research in the 2030s.