Tianzhou 6 launched! How was the "courier brother" of China's space program trained?

Produced by: Science Popularization China

Author: Space Brewing (Young Space Scholar)

Producer: China Science Expo

On May 10, 2023 Beijing time, China's manned space program ushered in the launch of the Tianzhou-VI cargo spacecraft: the Long March-7 rocket, like a giant dragon, took off from the Wenchang Space Launch Center. After the rocket and the spacecraft separated steadily, Tianzhou-VI quickly embarked on a journey to chase the Tiangong space station.

(Photo source: CCTV News Weibo)

This also means that after the Tiangong space station is fully built and enters the space application development stage, the upgraded Tianzhou spacecraft will be officially put into use.

The naming of Tianzhou continues the "Chinese romance" of China's space program in naming spacecraft. Its main function is to transport all kinds of materials to large manned spacecraft at the space station level. It is the "Tianzhou" that connects the heaven and the earth. In other words, it is the super "courier" of China's manned space program. Through Tianzhou-6, let's talk about how this super courier was made.

Before reading the following, let me ask you, what kind of express delivery do you like best?

"More! Stable! Fast! Cheap!"

"Only children make choices. I want them all!"

1. More: I can pull 7 tons of this kind of cargo!

Before troops move, food and grass must be sent first. Adequate material supply is the core factor that determines countless major undertakings. After the Tiangong space station is built, all kinds of consumption will need to be continuously supplied from the earth. Under the same conditions, the larger the capacity of the cargo spacecraft, the better.

The effect of the first flight of Tianzhou-1 and the docking with Tiangong-2 (the upgrade of Tiangong-1). The two are similar in shape, and the simple way to judge is to count the number of solar cells on one side. The Tianzhou on the left has three.

(Image source: Reference [1])

Currently, there are only four types of cargo spacecraft in service in the world, namely China's Tianzhou, Russia's Progress, and the United States' Cygnus and Dragon. Among them, Tianzhou's carrying capacity has reached an astonishing 6.9 tons, far exceeding the carrying capacity range of 2.2-3.3 tons of the other three spacecraft [1]. This is mainly because Tianzhou is developed based on my country's first experimental space station, Tiangong-1. Tiangong-1 is a big guy with a carrying capacity of 8.5 tons, almost reaching the upper limit of the capacity of the Long March 2F rocket. With the commissioning of the more powerful Long March 7 rocket, the developed Tianzhou can be greatly expanded, with a total weight of about 13.5 tons. The combination of a large rocket and a large spacecraft makes Tianzhou's carrying capacity ahead of other cargo spacecraft.

On May 7, 2023, the Long March 7 rocket and the Tianzhou 6 spacecraft were in vertical transfer.

(Photo source: Our Space)

Starting from Tianzhou VI, the spacecraft was further upgraded, especially the cargo capacity of the sealed cabin was greatly increased (increased by about 20%), and the overall capacity reached 7.4 tons, providing greater support for the space station [2].

2. Stable: versatile and absolutely reliable

For a cargo spacecraft, it is not enough to have a carrying capacity, but also to be a "jack of all trades" that can stably meet various needs. The consumption of the space station during operation is multifaceted, and Tianzhou took full account of various details at the beginning of its design.

Due to weak air resistance and other factors, orbit maintenance of large space stations consumes a lot of propellant. The Tianzhou spacecraft carries a large amount of propellant for in-orbit replenishment, turning it into a "space refueling truck". It can also start the engine after docking to help the entire space station raise its orbit, turning it into a "space trailer".

Astronauts are the soul of the space station's scientific research missions, and they themselves are also "scientific research payloads", giving birth to the corresponding aerospace medicine direction. The existence of humans means complex food, clothing, housing, transportation and life support needs, which are mainly completed through the sealed cabin of the Tianzhou spacecraft. Tianzhou-6 focused on strengthening the construction of the sealed cabin and enhancing the supply capacity. For example, Tianzhou-6 carried 70 kilograms of fresh fruit, which is twice the amount of fruit carried by Tianzhou-5, fully guaranteeing the needs of astronauts as "dry eaters".

After the space station is in orbit, it needs regular maintenance and replacement of important parts. Extravehicular activities also require regular consumption of extravehicular suits and auxiliary equipment. The experimental platforms inside and outside the cabin also need experimental materials, all of which need the support and transportation of the Tianzhou spacecraft. According to the characteristics of the device materials, some must be placed in the sealed cabin, while others can be "hook" in the non-sealed part, so as to maximize the transportation efficiency of the spacecraft.

The Tianzhou spacecraft is fully loaded with cargo, in addition to the extravehicular parts and propellant.

(Image source: Reference [1])

In addition, the Tianzhou spacecraft has continued China's glorious record of "0 failures" in manned space flight. It has currently achieved 5 successes out of 5 launches, making it a stable, reliable and all-rounder.

3. Fast: Rapid docking, space arrival within hours

Space flight is subject to various orbital dynamics constraints, which is very different from the ground transportation system that couriers on Earth face. Therefore, rendezvous and docking in space is a very difficult task: the spacecraft must be launched during a very small window period, then enter an elliptical orbit, and then repeatedly correct its orbit in order to meet the space station as scheduled. Under conservative circumstances, it usually takes about two days.

With the iterative development of the Tianzhou spacecraft, the spacecraft's orbital control capability has been improved, the orbit determination and navigation accuracy have been improved, and the control and guidance strategy has been continuously optimized, and the docking time has been continuously reduced. For example, Tianzhou-1 took two days to dock, but Tianzhou-5 completed the docking in just two hours! This is a new world record and the minimum theoretical time for a cargo spacecraft to meet the work requirements and ensure the success rate at the same time: docking is completed after one orbit.

The rendering of Tianzhou docking and servicing the entire space station

(Photo source: National Space Administration)

Therefore, the Tianzhou spacecraft, which performs the space-to-earth transportation mission, has achieved the efficiency of "hourly delivery" within the city. You can imagine such a scene: the astronauts see the order sent out at 9 o'clock in the morning and receive it at 11 o'clock, without delaying lunch.

4. Cheap: A highly cost-effective transportation solution

The direct benefit of the "more, more stable, and faster" Tianzhou spacecraft is that the frequency of use can be greatly reduced under the same capacity requirements. For example, the International Space Station needs to carry out about 8 cargo spacecraft resupply missions every year, while the new batch of cargo spacecraft represented by Tianzhou VI only needs 3 missions every two years to meet the operational needs of the Tiangong Space Station. "8 to 1.5", Tianzhou has a clear advantage in cost-effectiveness.

The reduction in the number of launches means that the use of launch site resources is reduced, the valuable time of the cargo spacecraft testing and maintenance team is also saved, the cost of expensive launch vehicles is greatly reduced, and the work arrangements of astronauts for nodes such as rendezvous and docking and spacecraft separation are also freed up. In addition, the launch and rendezvous and docking process of the Tianzhou spacecraft can use my country's data relay satellite system to achieve measurement, control and guidance, which greatly saves the corresponding costs. And after the breakthrough of key technologies (such as ultra-fast docking), spacecraft can be mass-produced, and the cost of a single one is greatly reduced.

Therefore, the powerful capabilities of the Tianzhou spacecraft can save a lot of money for my country's space industry, and these funds can be used to tackle other key technologies. Better technology can bring more output at a lower cost, and Tianzhou is an excellent example.

In the final stage of the mission, Tianzhou will do its best to maintain the space station's orbit for the last time, and try to improve its orbit to counter the influence of air resistance. Then it will leave the space station with a full load of garbage generated by the space station to make way for the subsequent spacecraft to dock. At the last moment, it will enter the Earth's atmosphere in a controlled manner. The violent impact and heat will turn it into a dazzling meteor. In order to prevent the impact of possible burning residues, it will generally aim at the huge "spacecraft cemetery" in the southern Pacific Ocean to end its glorious life.

References:

【1】Lei Jianyu Jia Dongyong Bai Mingsheng Feng Yong Li Xingqian . Research and Development of the Tianzhou Cargo Spacecraft. Space Sci Technol. 2023:3;0006. DOI:10.34133/space.0006.

[2] The new Tianzhou-6 cargo spacecraft will be launched in early to mid-May with more cargo, Guangming Online.