The Shenzhou 18 spacecraft is about to be launched, and many netizens compare the Shenzhou spacecraft with Musk's Dragon spacecraft, thinking that the Shenzhou spacecraft technology is too old.
Indeed, the Shenzhou 18 spacecraft actually still follows the structure of Shenzhou 5, and the spacecraft can be divided into three structures: single-cabin, double-cabin and three-cabin, of which the three-cabin spacecraft is the most advanced. The Soviet Union's first manned spacecraft, the Vostok 1 spacecraft, was a two-cabin structure consisting of a re-entry module and an equipment module.
When China developed the Shenzhou spacecraft, it gave up the development model of the first, second and third cabins of foreign advanced aerospace countries, and directly adopted the most advanced third-generation spacecraft technology at that time - the three-cabin configuration.
What is the three-cabin configuration
The spacecraft adopts a three-compartment structure, consisting of three compartments: the orbital module, the return module and the propulsion module, as well as additional sections. Wherein, the orbital module and the additional segment are located in the front part of the spacecraft, and the return capsule is located in the middle of the spacecraft, which is a sealed structure, and the shape is a bell-shaped large blunt-headed inverted cone, and the return capsule is located in the middle of the spacecraft, which is a sealed structure, and the shape is a bell-shaped large blunt-headed inverted cone.
The total length is nearly 9 meters, the total weight is about 8 tons, the crew is 3 people, and the astronauts in the spacecraft have 6 cubic meters of free space. The payload mass of the spacecraft is not less than 300 kg when it is put into orbit and 100 kg when it returns. Its reliability is 0.97, and the safety of astronauts is 0.997. The spacecraft can fly autonomously for 7 days and dock for 180 days.
The launch of Shenzhou-5 also marks that China has reached the level of the world's third-generation manned spacecraft with only one manned space launch mission. To this day, the third-generation spacecraft technology is still the mainstream spacecraft technology adopted by most countries (the only fourth-generation spacecraft that is truly practical at present is the Dragon spacecraft).
Generally speaking, a reusable manned spacecraft refers to a manned spacecraft that can be reused, can quickly pass through the atmosphere, freely travel between the earth's surface and space, transport crew and payload, and can also stay in orbit for a long time and maneuver in orbit to complete various tasks.
In fact, the research of multiplexed spacecraft is also a matter of nearly 10 years, and the only reusable manned spacecraft currently in the application stage is the Space Crew Dragon spacecraft, on May 30, 2020, the Crew Dragon spacecraft conducted the first manned flight test, sending 2 astronauts to the International Space Station, which is also the first practical application of the multiplexed spacecraft.
The Shenzhou spacecraft, although the technical architecture is still a three-cabin configuration. However, it is also enough for the construction and operation of the space station, and the Shenzhou 18 spacecraft has already been reborn compared with Shenzhou 5.
Shenzhou 18 has long been reborn
In fact, although the technical structure of the Shenzhou spacecraft has not changed, it has undergone many improvements and upgrades in appearance and technology. During the Shenzhou 7 mission, because there was an out-of-cabin mission, we canceled the additional section according to the characteristics of the mission, and made corresponding technical adjustments to the out-of-cabin function on the orbital module. Shenzhou 8 has added a docking mechanism, and starting from Shenzhou 16, the Shenzhou spacecraft's uplink and downlink capabilities have been greatly improved, and the maximum capacity will be increased by nearly 300%, which can better support the operation of the space station.
Not only that, the Shenzhou-18 manned spacecraft belongs to the second batch of products after the batch production of the "Shenzhou" manned spacecraft. This batch of products technically inherits the status of the previous batch of spacecraft, and further promotes the domestic substitution of components, while improving and upgrading the human-computer interaction interface of the spacecraft. These improvements are designed to improve the reliability and performance of the spacecraft.
Moreover, scientists found that after the Shenzhou spacecraft docked radially, it would be seriously obstructed by leaning there, and the Shenzhou spacecraft power system has a total of three power sources: solar cell sail board, cadmium nickel battery, and emergency battery. For more than 30 minutes after shading, the solar cell sail will stop working during the shadow period when there is no sunlight, and the power to maintain the normal operation of the spacecraft will come from the power stored in advance by the nickel-cadmium battery. In order to solve the problem of energy balance, after the successful rendezvous and docking, the space station needs to provide some electrical energy for the Shenzhou spacecraft.
In order to ensure the stability of the space station system, Shenzhou 18 ushered in a major upgrade, the battery was replaced with a lithium battery, the lithium-ion battery has high capacity, light weight and other excellent performance, a prominent advantage of lithium-ion battery compared with nickel-cadmium battery is that there is no memory effect, and the life advantage will also help the Shenzhou spacecraft to have a longer time to berth the space station assembly. According to the research of scientists, lithium batteries have a long cycle life, the number of cycles can reach more than 1000 times, in the case of balanced charging and discharging, the service life can reach 5~10 years, and the life span is about 2 times that of nickel-cadmium batteries.
Not only the Shenzhou spacecraft, but also the Long March rocket that launched the Shenzhou spacecraft is also constantly improving and upgrading, and the reliability assessment value of the Long March-2F launch vehicle has been increased to 0.9896, and the safety assessment value has reached 0.99996. Compared with the Chang-2F Yao-17 carrier rocket that launched Shenzhou-17, the Yao-18 rocket that served as the launch mission has made more than 30 technical status improvements to further improve the reliability and safety of the whole rocket.
A new generation of manned spacecraft is already on the way
It can be said that the technology of the Shenzhou 18 spacecraft has long been not comparable with the Shenzhou 5, of course, China has also developed a new generation of manned spacecraft, compared with the Shenzhou spacecraft, the new generation of manned spacecraft adopts a new design, larger size, and adopts a modular design, which can not only take into account the manned and cargo missions in low earth orbit: it can carry 6~7 astronauts when performing manned missions, which is double that of "Shenzhou"; when performing cargo missions, it can carry 4 tons uplink and 2.5 tons downward. It can carry both people and cargo, and can also take into account deep space launch missions such as the moon landing by changing the service module, and will become a heavy-duty multi-functional manned spacecraft on the same level as the American "Orion" and the Russian "Federation".
In 2020, China's new generation of manned spacecraft test ship was successfully launched, and further tests are needed, which cannot be used during the construction of the space station, so the new generation of manned spacecraft mainly serves the space station operation period and the manned lunar landing. This is another reason why the Shenzhou spacecraft is still on mission.
China's Shenzhou spacecraft adopts batch construction, with a maximum of 6 ships in a batch, which means that after Shenzhou 21, China may adopt a new generation of manned spacecraft.