What "space express" did Tianzhou-4 send?

At 1:56 a.m. on May 10, starting from the Wenchang Cosmodrome, the fourth cargo spacecraft on the mainland, the Tianzhou-4, was successfully launched by the Long March 7 Yao-5 carrier rocket. As the first launch of the space station mission in 2022, it opened the prelude to the construction phase of the Chinese space station in orbit.

Photography: Tu Haichao

More than 200 pieces (sets) of cargo supplemental propellant is about 750 kg, and the total weight of uplink materials is about 6000 kg

Astronauts are stationed on the space station for a long time, and the materials needed to eat, wear, use and even breathe must be supplied by logistics to the spacecraft - the cargo spacecraft is sent to the space station in time, and the fuel required for the space station to maintain the correct orbit is also transported by the cargo spacecraft. Last year, the Long March 7 rocket sent the Tianzhou-2 and Tianzhou-3 cargo spacecraft into space, completing the replenishment task during the construction phase of the space station. This time, Tianzhou-4 once again transported supplies to the space station in advance before the Shenzhou 14 astronauts entered the space station in a group.

According to reports, the Tianzhou cargo spacecraft adopts a type spectrum scheme, designs a fully sealed, semi-sealed semi-open, and fully open cargo compartment module that meets different cargo transportation needs, and combines with the general propulsion module to form a fully sealed cargo spacecraft, a semi-sealed semi-open cargo spacecraft and a fully open cargo spacecraft. Tianzhou-4 cargo spacecraft is a fully sealed cargo spacecraft, is the world's largest active cargo transportation capacity, the most comprehensive on-orbit support capacity of the cargo spacecraft, undertakes the task of providing material support for the Shenzhou 14 crew, space station operation support and space science experiments, during the docking of the space station will be the implementation of cargo supply, propellant replenishment, space science experiments.

In this mission, Tianzhou-4 loaded more than 200 pieces (sets) of cargo in total, including cargo packages and direct installations, carrying about 750 kilograms of retro-propellant and a total weight of about 6,000 kilograms of uplink materials, which will provide material support for the 3-person crew of Shenzhou XIV to stay on orbit for 6 months, assemble and build the space station, carry out material science, microgravity, aerospace medical experiments and other space application fields.

In order to ensure the safe delivery of goods to the "Space Home", Tianzhou-4 adopts a variety of cargo loading methods such as cargo bags, brackets, and storage boxes, and the types and quantities of goods can be dynamically configured according to the needs of the space station; at the same time, it also has the ability to undertake space station operation support tasks such as space station attitude orbit control, grid-connected power supply, space station telemetry, data transmission support, and space science experiment support capabilities.

In the process of developing the Tianzhou cargo spacecraft system, the research and development team of the Fifth Academy of China Aerospace Science and Technology Group Co., Ltd. made improvements and optimizations based on the opinions of the previous astronaut crews on-orbit use.

In order to find goods more convenient and intuitive, Tianzhou-4 has increased the color marking of cargo bags through the color design of labels and handles; in order to facilitate astronauts to operate the loading adapter plate in orbit and avoid accurate alignment screws every time, Tianzhou-4 began to add buckle belts to the adapter plate and corresponding shelves to achieve convenient anti-drifting during the orbit; in order to reduce the on-orbit space occupation of buffer packaging materials, facilitate storage and storage, miniaturize and optimize the design of the buffer foam in the cargo bag, and increase the buffering scheme of the gas column to reduce weight. These ingenious designs have made the logistics support and replenishment capabilities of the Tianzhou-4 cargo spacecraft stronger.

The Changqi rocket and the Tianzhou cargo spacecraft "joined hands" to go to space for the fourth time, and the two have been very "tacit understanding"

The Long March 7 rocket is a new generation of medium-sized carrier rockets developed to meet the needs of the space station project to launch cargo spacecraft. The Long Seven rockets, which carried out the first battle, made a good start for the Long March 2 F and Long March 5 B carrier rockets.

2022 marks the 30th anniversary of the implementation of China's manned space project, and it is also the year of decisive victory in the construction of the space station. According to the mission arrangement, a total of 6 flight missions were carried out throughout the year, and the space station Qingtian Capsule, the Dream Sky Capsule, the Two Tianzhou Cargo Spacecraft, and the two Shenzhou manned spacecraft were launched through the Long March 5 B, Long March 7 and Long March 2 F III carrier rockets.

According to Shao Yetao, chief designer of the China Launch Vehicle Technology Research Institute of China Aerospace Science and Technology Group Co., Ltd., this is the fourth time that the Changqi rocket and the Tianzhou series cargo spacecraft have "joined hands" to go to space, the two have been very "tacit understanding", the overall technical state of the rocket has gradually stabilized, and the flight reliability assessment value has reached the international advanced level of 0.9838.

In this mission, the rocket has a total of 17 technical state changes, such as pre-launch process optimization and reliability improvement. For example, the parallel filling of liquid oxygen kerosene on the day of launch reduces the pre-launch preparation time, reduces the requirements for conditions such as meteorological support of personnel and equipment, and improves the reliability of the launch... Through a series of measures, the Long Seven rocket was tested and launched in one month for the first time.

In order to send a cargo spacecraft carrying a large number of materials into space on time, it is necessary to have a carrier rocket with sufficient capacity, great "strength" and high reliability. The total weight of the Changqi rocket is more than 500 tons, the weight of the arrow shell, cable, instrument and so on is only more than 50 tons, and the rest is the weight of liquid oxygen kerosene propellant, more than 90%.

Rocket experts say that rockets are "special vehicles" that lead to space with satellites and other payloads, and the smaller the weight of the car itself, the better, and the more fuel that can provide power, the better, so that as much "transportation" as possible can be left to "passengers".

The Long Seven rocket has a low-Earth orbit carrying capacity of 13.5 tons, more than half more than half that of carrier rockets using conventional fuels. Among them, 6 liquid oxygen kerosene engines on the core stage and booster provide more than 700 tons of takeoff thrust.

Xu Lijie, a rocket design expert in the overall department of the Rocket Institute, said: "The greater the proportion of fuel in the entire weight of the rocket, the higher the structural efficiency of the rocket, indicating that the more reasonable the design." In the design, he said, they designed the rocket's shell, cables, instruments and other components as simple and powerful as possible to reduce weight.

The design reliability of the Changqi rocket has reached the domestic leading position. In order to cope with the humid, hot, rainy and typhoon-prone marine climate in Hainan, the Long March 7 rocket has an all-weather launch capability, which can be parked for 24 hours after the low-temperature fuel is refueled, and strive for more favorable time for the successful launch.

Zhu Pingping, a rocket design expert of the General Department of the Rocket Institute, said that the new generation of carrier rockets represented by the "Long Five" and "Long Seven" are liquid hydrogen, liquid oxygen and liquid oxygen, kerosene, which are low-temperature fuels, of which the temperature of liquid hydrogen reaches minus 253 degrees Celsius, and the temperature of liquid oxygen reaches minus 183 degrees Celsius. Liquid hydrogen and liquid oxygen combustion produce water, non-toxic and non-polluting, and greatly improve the carrying capacity of the rocket.

Source: People's Daily client