"Dreaming" about the Tiangong: Unveiling the Mengtian Experimental Module and its Development Process

" , one, L, T ..."
From "blank" to "one" configuration, to L configuration, and then to the T configuration that is about to be formed, these simple symbols are the 30 years of hard work of manned space engineering. From the establishment of the "921 Project" to the successful launch of the Dreamliner today, China's manned space engineering is finally about to write the final chapter of the third story.

The Long March 5B rocket lifts the Dreamliner spacecraft into space. Photo by Su Dong

"Mengtian" is one of the last protagonists to appear.

“Building a temple in a snail shell”

The Mengtian Experimental Module consists of four sections: the working module, cargo airlock module, payload module, and resource module. The module is 17.88 meters long, with a maximum diameter of 4.2 meters and a launch mass of about 23 tons. It is equipped with a large flexible solar wing with a power generation capacity of up to 13.5 kilowatts and an unfolded area of ​​138 square meters. There are 13 standard payload cabinets inside the module and 37 payload installation stations outside the module, which provide stronger support for scientific experiments on the space station.

This is the official introduction of "Mengtian", but there is a little-known story behind "Mengtian".
On May 23, 2012, the state clearly stated in the approval of the division of labor and designated points for the space station system that the Eighth Academy of China Aerospace Science and Technology Corporation was responsible for the overall development of the space station experimental cabin II. At the beginning of the plan, the experimental cabin II was called the survey optical cabin, and the survey telescope was only a component of the experimental cabin. However, during the operation of the space station, factors such as excess objects, vibration, attitude adjustment, and orbit control will interfere with the operation of the telescope, and the observation direction of the survey telescope will interfere with the operation of the space station, which is contradictory.

Later, with the improvement of my country's aerospace capabilities and after multiple considerations, the survey telescope separated from the experimental cabin and flew with the space station.

This was a win-win situation, but it caught the Mengtian Laboratory Cabin team off guard. This meant that their previous design faced extensive changes, or even had to be overturned and rebuilt. The dual pressures of sunk costs and the impending mission deadline made everyone in the team think deeply.
"After the redesign, we positioned 'Mengtian' as a place for astronauts to work, supporting various scientific experiments inside and outside the cabin," said Fan Ping, senior engineer and chief designer of the 805 Institute of the Eighth Academy.

The scientific research team took a group photo with the Dream Sky Cabin. Photo provided by the Eighth Academy

While maintaining the original structural configuration and platform functions unchanged, the new plan innovatively proposes a "cargo airlock" function, adds a cargo entry and exit airlock compartment, and cleverly adopts a nested structural configuration, turning the "three compartments" into a "four compartments".

The redesigned "Mengtian" work cabin is at the front end, connected to the core cabin through a docking mechanism. It is oriented towards microgravity science research and is equipped with 13 experimental cabinets in multidisciplinary fields such as fluid physics, material science, combustion science, basic physics and aerospace technology experiments. It also provides astronauts with a nearly 32 cubic meter "Dream Factory" studio. The payload cabin and the cargo airlock cabin are connected in a unique "double-cabin nesting" form, that is, a cargo airlock cabin is hidden inside the payload cabin, and the "main" cargo exit channel. At the front end of the resource cabin is where the sun-orientation device and flexible solar wings are installed.

"The newly designed experimental cabin also solves the problem of large-sized payloads being unable to exit the cabin from the airlock. In Shanghai dialect, it is like 'doing a ritual in a snail shell.'" said Liu Huiying, the project manager of the Mengtian experimental cabin. They also equipped the payload cabin with two deployable exposure platforms and an embedded fixed exposure platform, which is 15 square meters in size and can be equipped with a large number of load exposure points outside the cabin.
It can be said that today's "Mengtian" is the biggest boost to my country's construction of a national space laboratory with world-leading level.

"Goods-oriented" and "people-oriented"

The core of manned space flight is people.

One of the important purposes of manned space flight is to give full play to the role of people on the scene, such as their subjective initiative in dealing with problems and their delicate operating ability. However, people's working ability, especially their delicate operating ability, varies greatly inside and outside the cabin.

During extravehicular activities, the observation effect, operating space and tool use ability of people are greatly restricted by the space suits and gloves. Even with special design and special tools, it is far from the precision level of the work inside the cabin. In the cabin, it can be said that as long as the tools are suitable, the work that can be done on the ground can be completed by astronauts in orbit.

A close look at the Dream Sky Cabin. Photo courtesy of the Eighth Hospital

Therefore, "Mengtian" provides a unique function of automatic cargo entry and exit, creating more suitable working conditions for astronauts in space, and achieving "cargo-oriented, but people-oriented".

Unlike the Wentian laboratory module, the airlock of the Mengtian spacecraft is no longer used for astronauts to exit the spacecraft, but is a dedicated passage for cargo to exit the spacecraft. Before this, astronauts usually "exit the spacecraft to bring cargo" to transfer and install cargo inside and outside the spacecraft, but this method is often limited by the number of astronauts' exits, the number and size of payloads, and astronauts who frequently conduct extravehicular activities will face more complex safety tests in the space environment.

The cargo airlock of Mengtian adopts a double-door design of "inner door + outer door": the inner door leading to the working cabin is a key device for isolating the space environment inside and outside the cabin; the outer door facing the earth is the exit for cargo to the outside of the cabin. In order to ensure the safety of astronauts in orbit, the inner and outer doors will not be opened at the same time.

Taking the cargo extravehicular mission as an example, the astronauts set up the payload in the cabin and install it on the automatic transfer mechanism; the personnel evacuate the airlock, return to the working cabin and close the door; the airlock is depressurized; the cabin door is opened and the transfer mechanism sends the payload out of the cabin; the robotic arm grabs and takes away the payload; the transfer mechanism is withdrawn into the cabin; and the personnel can enter the airlock to carry out normal work.

"The transport capacity of the load transfer mechanism reaches 400 kilograms, and the envelope size of a single cargo transport can reach 1.15 meters × 1.2 meters × 0.9 meters," said Liu Huiying.

After the use of the cargo airlock, astronauts will no longer need to wear extravehicular spacesuits to send or bring back payloads, which greatly reduces the safety risks of such operations and extends the service life of spacesuits.

The interior of the Dream Sky Cabin with on-site staff.

The automatic airlock provides a transitional workroom between the inside and outside of the cabin, where large payload components can be assembled and tested before being sent out of the cabin as a whole. The payload outside the cabin can also be moved here first, and after re-pressurization, the astronauts can disassemble, repair, and maintain it in the same way as inside the cabin.

Furthermore, astronauts can also assemble microsatellites in the Mengtian module and have them transferred outside the module for release.

"Mengtian can support the on-orbit assembly and automatic release of 36U cubic satellites or 100-kilogram microsatellites," said Li Lichun, chief mechanical designer of the Mengtian laboratory module of the space station. "The volume of 1U is 10 cm x 10 cm x 10 cm, which can be held in the palm of your hand."

“1+1+1=1”

The unified three-module system of the space station is a unique advantage of my country's space station.

Following "Tianhe" and "Wentian", once "Mengtian" is transferred to dock and completes system integration, China's Tiangong space station will make another qualitative leap.

Looking at the space stations around the world, the Mir space station has modules arranged on multiple planes, and the problem of solar panels blocking the spacecraft is prominent. The entire International Space Station relies heavily on the Zvezda service module, the core module, for attitude and orbit control. Once there is a problem with this module, the entire station will be greatly affected.

The Tiangong space station emphasizes the system unification of the three modules of the space station based on the analysis and reference of the design concepts, experience and lessons of the Mir space station and the international space station. Extravehicular activities are backed up by dual airlock modules, attitude and orbit control is backed up by "Tianhe" and "Wentian", and "Mengtian" can also back up key functions. The three modules are distributed in the same plane to ensure that the solar panels are not blocked... Through three launches in steps, the assembly and construction are completed in orbit, forming a powerful and complete 70-ton "Tiangong", which can achieve higher research and development benefits under the conditions of moderate scale, obtain efficient resource utilization and stronger system redundancy.

The rendering of the T-shaped configuration of China's space station. Image provided by the Eighth Academy

After the docking and transfer, it will take about a week for Mengtian to integrate its own resources into the space station complex and realize the grid-connected management of control, energy, information, environment and other functions with the other two cabins of the space station. By then, the space station will complete another system integration after the assembly of Wentian.

On the one hand, after the system is integrated, the energy of the three cabins is connected to the grid and managed in a unified manner. The two experimental cabins can allocate energy across cabins and be connected through a thermal control and heat dissipation circuit to implement heat dissipation capacity allocation that matches the energy supply.

For example, if the "Mengtian" load is started up more frequently, and the cabin power generation alone may be short of 1 kilowatt, then 1 kilowatt of electricity can be allocated from the "Wentian" to enter the power grid. At the same time, the "Mengtian" can transmit the excess heat it generates to the "Wentian" and safely dissipate it through the "Wentian" radiator.

On the other hand, after the system is integrated, the three-cabin platform and payload information can be managed in a unified manner. Various information networks are combined, and the platform bus, payload Ethernet and its equipped WiFi are all connected to the network, which can realize the system's indiscriminate monitoring and management of equipment in any compartment, which is conducive to the unified allocation and dynamic management of the entire station's payload resources.

The rendering of the Mengtian capsule being assembled on orbit. Image provided by the Eighth Academy

In addition, after the system is integrated, the living and working environment provided by the three cabins for astronauts can be managed in a unified manner. The sealed spaces of the three cabins are connected to form a complete air circulation, and the air pressure, composition, temperature and humidity can be uniformly controlled and evenly distributed with the air flow, allowing astronauts to be in a suitable environment in each cabin.

Through system integration, the equipment in each module can be deployed and reconstructed on demand. There will also be changes to varying degrees in the control system and robotic arm applications. This is all due to the advanced system design of my country's space station.

Today, as the main module of the national space laboratory, "Mengtian" will greatly enhance my country's space station's ability to conduct scientific experiments in orbit. It may have new key breakthroughs in a large number of cutting-edge fields such as technology development and application, biology, physics, etc., thereby promoting scientific and technological development and "bringing" the distant future closer.

At that time, in the deeper space, there will be traces of the Chinese people left.