How is the "big belly" of Tianzhou-6 different from the previous ones?

At 9:00 a.m. on May 30, the Shenzhou 16 manned spacecraft was successfully launched on the Long March rocket.

As the first manned flight mission of my country's manned space program entering the space station application and development stage, Shenzhou XVI and the Tianzhou VI cargo spacecraft successfully launched more than half a month ago, one carrying people and the other carrying goods, can be described as the "twin peaks" of China's space transportation.

Cargo spacecraft are the "space couriers" that travel between heaven and earth . They mainly deliver propellants, fuel, food, etc. to the space station, and collect the waste in the space station together. Eventually, they will burn up in the atmosphere together with the waste and fall into the ocean area on the earth farthest from humans.

my country has currently launched a total of six cargo spacecraft, namely Tianzhou-1 to Tianzhou-6.

Tianzhou-6 is the world's largest cargo spacecraft in service, and is also the first cargo spacecraft in a batch of Tianzhou-6 to Tianzhou-11. It is of great significance for the verification of the technology of the same batch of spacecraft and the mass production of subsequent spacecraft.

Congratulations on the successful launch of Tianzhou-6 (Source: watermark)

Unlike the previous five, Tianzhou 6 has been improved and innovated in terms of transportation, power system and loading capacity. This different "big belly" has saved the country hundreds of millions of yuan.

A simulation of the Tianzhou-6 cargo spacecraft in orbit

Source: Xinhua Daily Telegraph, image provided by the Eighth Academy of China Aerospace Science and Technology Corporation

Different transportation

During the transportation of Tianzhou-6 to the launch site, the cabin was in an upright position , while the first five Tianzhous were in a lying position.

After the first five Tianzhous were built, the staff disassembled the extravehicular equipment and transported the cabin and extravehicular equipment to the launch site by shipping, and then installed and tested them. This time-consuming and laborious work is more suitable for the initial stage of cargo spacecraft development.

In order to improve efficiency, the R&D personnel decided to transport the Tianzhou-6 capsule in an upright position, with all the extravehicular equipment except the solar cells carried with the capsule. This way, after arriving at the destination, it can be launched after a simple installation and testing.

The upright state of Tianzhou-6 during transportation determines that its packaging and route are different. Researchers have created a new set of flexible ship clothing for Tianzhou-6, which can not only block the impact of high temperature, humidity and high salt fog environment on the spacecraft, but also prevent rain, dust, lightning and pollution. In addition, the cabin packaging box is made of aluminum alloy and is equipped with air conditioning and vibration reduction, automatic exhaust, inspection and control systems.

Tianzhou-6 is being transported to the Wenchang launch site (see watermark for image source)

In addition, the Tianzhou-6 packaging box is equipped with four fans to ensure that the nitrogen in the packaging box is evenly distributed, ensuring that the atmospheric pressure in the box is higher than the outside air pressure (because the density of evenly distributed pure nitrogen is much greater than the density of air), and preventing salt spray from the sea from entering the packaging box and corroding the cabin and products . Salt spray refers to tiny droplets of salt in the sea air, which are mainly formed by foam generated by wind, waves hitting the shore, and the rupture of foam. Salt spray corrosion is one of the common atmospheric corrosions, which can destroy the protective layer of metals or alloys, reduce mechanical strength; or interrupt the power supply lines of electronic components and wires.

The vertical cabin occupies an area of ​​about 96 cubic meters, which means that the transportation method must be exquisite. For this reason, the R&D team adopted a land and sea method. After the cabin is produced in the Beijing factory, it is transported by land to the Tianjin port, then shipped from the port to the Wenchang Space Launch Center in Hainan by sea. Although this takes more than ten hours more than the previous air transportation, it is undoubtedly more reliable and safer for the upright cabin.

Different power systems

The power supply system provides energy for Tianzhou-6 to travel between heaven and earth, and plays an irreplaceable role.

To this end, researchers have been working to improve the power system of Tianzhou-6 since 2019. After more than three years of exploration, they finally developed a solar panel operating mode that is more suitable for in-orbit operation in space.

When the solar incident angle is small and there is little sunlight, the solar panels enter a "semi-sleep" state, and the system is powered by the Chinese space station. When the solar incident angle is large enough and there is a lot of sunlight, the solar panels wake up from "semi-sleep" and obtain energy from the sunlight to ensure the operation of the cargo ship.

This mode is flexible and can fully utilize the space environment above the earth to obtain energy. The amount of electricity generated by it is enough for an ordinary family to use for more than half a month, ensuring the power supply needed for Tianzhou-6 to "carry goods" and for astronauts to stay in orbit and carry out work.

Tianzhou-6's power configuration and related data (Source: Shanghai Airlines)

It is worth mentioning that starting from Tianzhou 6, the key components of the Tianzhou power system have been 100% localized , which is 15% higher than the localization of the previous Tianzhou power components. This not only improves the reliability of the power supply, reduces costs, meets the needs of uplink remote control and downlink images and payload data, but also greatly enhances the confidence of the Chinese people.

Different loading capacity

In terms of transportation, cabin status, packaging and power supply system, the loading capacity of Tianzhou-6 has been greatly improved compared with the previous five Tianzhous.

Like the other five Tianzhou spacecraft, Tianzhou-6 is also divided into two cabins: one is the cargo cabin responsible for transporting materials, also known as the sealed cabin ; the other is the propulsion cabin that performs flight missions, loads propellants and provides power and energy for the spacecraft. Obviously, to improve the loading capacity of the spacecraft, we have to start with the two cabins.

Simulation of the cargo compartment and propulsion compartment of Tianzhou-6 (Source: Shanghai Airlines)

First, the demand for propellant in the space station has decreased, and the space in the propulsion module has become larger. Previously, because the Chinese space station was under full construction, most of the space in the propulsion module was loaded with propellant for construction. After the completion of the Chinese space station at the end of 2022, the demand for fuel has decreased, and the space in the propulsion module has become larger. Previously, there were 8 propellant tanks in the Tianzhou propulsion module, and the number has been adjusted to 4 since Tianzhou 6.

Second, some equipment will be transferred to the propulsion module, and the cargo compartment will be larger. The more things Tianzhou-6 can carry in a single trip, the more economical and capable it is. The size of the cargo compartment is the main indicator of Tianzhou-6's loading capacity. The increase in cargo compartment volume can reduce the number of launches and improve mission capabilities.

The cargo compartment has a larger volume, so it can naturally provide astronauts with more supplies for a longer time. The part of the propulsion compartment that originally held fuel is now used to hold nearly 30 sets of equipment and instruments in the original cargo compartment. The cargo compartment has been expanded by 20%, and the loading capacity has increased by 1.2 tons. Previously, 5.5 tons of cargo could be transported in the sealed compartment, but now 6.7 tons can be transported. This is how the "cosmic-level cargo delivery" of 70 kilograms of fresh fruit (about twice the fruit carried by Tianzhou-5) for the astronauts of the Chinese space station was finally realized.

According to statistics, with the increase of cargo loading space in the Tianzhou-6 sealed cabin, the cargo loading capacity of the entire ship has increased from 6.9 tons to 7.4 tons, and the uplink (lift-off) cargo ratio has increased from 0.51 to 0.53. The cargo ratio refers to the ratio between the weight of the cargo carried and the total weight of the entire spacecraft. The higher the cargo ratio, the more efficient the spacecraft is in carrying cargo. The uplink cargo ratio of Tianzhou-6 is 0.53, which means that it has the strongest carrying capacity among the current cargo spacecrafts.

Cost estimation of the Tianzhou spacecraft (Source: Shanghai Airlines)

The International Space Station needs to launch about 8 cargo spacecraft every year. According to the calculation of the first five "Tianzhou", the Chinese space station needs to be resupplied twice a year. According to the carrying capacity of Tianzhou 6, three resupply every two years can meet the demand, which means saving 0.5 times a year. Calculated at a cost of about 350 million yuan per cargo spacecraft, it can save 175 million yuan for the country every year. In this respect, Tianzhou 6 may be the most cost-effective "big belly" in the world!

References:

1. “Tianzhou spacecraft ‘upgraded version’ opens a new stage for space station”, People’s Daily, May 22, 2023

2. "Boat Travels Across the World, Carrying Dreams on a Journey", by Liu Shiyao and Yu Sinan, People's Daily, May 11, 2023

3. "Tianzhou, China's Space Ferry Cargo Barge", author Liu Haochi, "Aerospace Knowledge" 2021 Issue 6

Author: Wei Deyong, member of Shenzhen Writers Association, Guangdong