What is the secret to making the space station “sit like a clock and move like the wind”?

On July 24, the Wentian Experimental Module was successfully launched at the Wenchang Space Launch Center. After the Wentian was commissioned, the current space station complex consists of the Tianhe core module, the Wentian Experimental Module, the Shenzhou XIV manned spacecraft and the Tianzhou IV cargo spacecraft. This year, it will also welcome the Mengtian Experimental Module, Tianzhou V and Shenzhou XV. The difficulty of attitude control of this space station complex with an in-orbit mass of more than 100 tons is unprecedented in my country's space flight missions. The sixth episode of "Questions about the Heaven" will answer the secret of making the space station "sit like a bell and move like the wind"!

Is there a “magic weapon” for spacecraft attitude control?

Controlled moment gyro shows its prowess

The traditional method of attitude control for spacecraft is to adjust the attitude through the RCS attitude control power system (Reaction control system), which requires upward travel and consumes a large amount of propellant. It has a very low cost-effectiveness and is not suitable for attitude control of large spacecraft.

During the daily operation of the space station, its attitude will change due to the influence of many factors such as the Earth's upper atmosphere, solar electromagnetic radiation, and gravitational field. The many payloads on board also have specific pointing requirements, especially the large flexible solar wings have dynamic solar orientation requirements.

⬆️Large flexible solar wing for space station

Therefore, the stable operation of the space station requires a powerful "artifact" that can stabilize it - the control torque gyro . It is an inertial actuator for the attitude control of the spacecraft. It obtains angular momentum through a high-speed rotating flywheel and outputs torque to the outside by changing the direction of the angular momentum. Compared with the RCS attitude control system, in addition to the natural advantage of zero fuel consumption, it also has the advantage of minimizing interference with the flexible components of the spacecraft. For large space stations, it is an indispensable core technical equipment.

⬆️Control torque gyro

It was once a "stumbling block" to technological development!

Now we are self-reliant and make smart products

It is impossible to thread a needle through a thousand miles without it; it is impossible to build a space station without it; it is impossible to develop a fast maneuvering spacecraft without it... The technical research and product development of the control moment gyro was once a "stumbling block" for the development of China's space technology. In 1991, my country began to demonstrate the space laboratory and space station projects, and the control moment gyro was proposed as a "heavy weapon". The Chinese people were convinced that "core technology cannot be bought", so they firmly chose self-reliance at the beginning of the demonstration.

The first 200Nms (Newton-meter-second) control torque gyro that my country sent into space. Six such gyro were installed on the Tiangong-1, which was successfully launched into orbit in 2011. Its on-orbit application has become a milestone in the development of my country's space electromechanical components, and has also made my country the third country in the world to master this technology after the United States and Russia.

⬆️200Nms control torque gyro

Since Tiangong-1, the research team has successively developed products with angular momentum ranging from 0.1Nms to 1500Nms , forming a full range of control moment gyroscope products that meet the attitude maneuvering and attitude control requirements of various types of spacecraft in China. Compared with the first generation of products, the newly developed control moment gyroscope has the advantages of high precision , fast response , long life , and high reliability , which can meet the attitude control requirements of various types of spacecraft in China .

The space station mission has taken the use of control moment gyros on Chinese spacecraft to a new level. The control moment gyros of other spacecraft are installed in the cabin, and the working environment is relatively simple, while the control moment gyros on the space station need to adapt to both the cabin and the outside working environment. Due to factors such as the huge temperature difference and vacuum degree changes, the lubrication of key parts of the product and the heat dissipation of the whole machine have brought great challenges, especially for the temperature difference of more than 200 degrees outside the cabin. The developers must carry out special thermal control design, and carry out vibration and noise reduction work on the cabin products to meet the cabin noise index requirements.

⬆️Six large control torque gyroscopes have been installed in the core module of the space station

As a complex space electromechanical product, the control moment gyro has a harsh working environment and a long lifespan. It is required to work continuously for many years at thousands of revolutions per minute, and the probability of failure in orbit is relatively high. Therefore, in order to ensure the life and reliability of the space station, the control moment gyro must also have the ability to be replaced in orbit .

The control moment gyroscope used in the Chinese space station has the largest angular momentum of 1500Nms, and adopts a "6+6" configuration in two cabins. Six of them have been installed on the outer wall of the cone connecting the large column section and the small column section of the core cabin, and the other six will be installed in the Wentian experimental cabin. This configuration is the advanced feature of the system level of the combination, which can be integrated and reconstructed on demand through the general network.

⬆️Shenzhou 14 astronauts set up the control torque gyro in orbit

From a "stumbling block" to a technological peak, the development and application of the control moment gyro series products have significantly improved the attitude maneuvering and attitude stability control capabilities of my country's spacecraft, and also promoted the rapid development of my country's space inertial actuators. The joint use of multiple control moment gyros is enough to help the space station "sit like a bell and move like the wind", and promote the steady development of manned space engineering.

(Beijing Institute of Control Engineering, China Academy of Space Technology)