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PALACE IN THE SKY

Based on the experience of previous designs like the ISS, China’s Tiangong space station minimizes assembly, construction and operation costs while maximizing its experimental capabilities

By NewsChina Updated Sept.1

Tiangong space station in orbit after docking with the Tianhe core module

On June 17, a Shenzhou-12 rocket blasted off from Jiuquan Satellite Launch Center in northwest China with three Chinese astronauts on board. The spaceship docked with the Tianhe core module of China’s orbiting Tiangong space station.  

Veteran astronaut Nie Haisheng, 56, on his third trip to space is the mission leader, accompanied by crewmates Liu Boming, 54, on his second trip, and rookie Tang Hongbo, 45. 
 
The three-month trip marks the longest stay by Chinese astronauts in space to date. Over the next two years, China plans to send nine astronauts to the space station and launch three freight transport spacecraft, carrying out a total of 11 missions.  

The astronauts on the Tiangong (Heavenly Palace), see the sun rise and set every 90 minutes, and live in a zero-gravity environment. An important purpose of the space station is to conduct large-scale experiments and test technology applications. It represents the most advanced scientific achievements in Chinese aerospace technology.  

“China’s space station has the late-mover advantage. Many technologies are developing rapidly, so our construction period is greatly reduced,” Yang Hong, chief designer of Tiangong and the Tianhe core module, told NewsChina.  

“Drawing on the experience and lessons of foreign space stations, we can minimize the assembly, construction and operation costs and facilitate scientific experiments to the greatest extent,” he added.  

Pang Zhihao, a retired spaceflight researcher at the China Academy of Space Technology, told NewsChina that Tiangong is considered a third-generation space station due to its smaller scale, and like the International Space Station (ISS), has multiple docking ports. Secondgeneration stations like the US’s Skylab (launched in 1973) had two docking ports and a first-generation like the USSR’s Salyut 1 (1971) had only one. 

“Some technologies used in the construction of the space station are on par with advanced international levels,” he said.  

Tiangong vs ISS 
The development of space stations worldwide has clear watersheds. Jiao Weixin, an aerospace professor at the School of Earth and Space Sciences of Peking University, told NewsChina that space stations can be roughly divided into two types, the single module and multi-module structure.  

China’s previous space lab prototypes, Tiangong-1 and Tiangong-2 were single-module space stations, neither of which are still in orbit.  

China’s Tianhe core module is a third-generation space station. On April 29, the core module was launched, which serves as the command center and crew cabin.  

Compared with the ISS, China’s space station is lighter and smaller, as well as cost-effective in terms of performance, according to Jiao.  

“For example, the weight of the equipment used in scientific experiments is lighter than that aboard the ISS,” he said.  

Jiao told NewsChina that the ISS weighs 420 tons. The structure, including its solar arrays and robotic arms, spreads across 8,000 square meters, the equivalent of a soccer pitch, and it has living space equivalent to a five-bedroom house. China’s space station, comprised of one core module and two experiment or lab modules, only covers a few hundred square meters. 
 
NASA (the US), Roscosmos (Russia), JAXA (Japan) and the ESA (Europe) each have an experiment module on the ISS mainly used for research, accounting for less than 20 percent of the weight of the ISS. In comparison, roughly 66 percent of the weight of Tiangong space station comprises of the experiment modules. Spaceflight expert Pang Zhihao said the ISS is not comparable to China’s space station in terms of coordination, integration and efficiency because participating countries built their own modules separately.  

Chinese President Xi Jinping congratulates the three astronauts aboard the Tiangong space station’s Tianhe core module via videolink from Beijing Aerospace Control Center, June 17, 2021

Life Without Gravity 
A spacious and comfortable environment and maintaining physical health are essential for astronauts to cope with life in space.  

Compared with the labs on Tiangong-1 and Tiangong-2, each of which weighed about 8.5 tons, the Tianhe core cabin module is China’s largest spacecraft. At 16.6 meters long with a maximum diameter of 4.2 meters, Tianhe is larger than any cabin module on the ISS.  

The astronauts on China’s first manned space mission, the Shenzhou-7 spacecraft, had quarters of about 7 cubic meters and about 15 cubic meters on Tiangong-1. The Tianhe core cabin module is 50 cubic meters. When the next two experiment modules are launched next year, the total space will reach 110 cubic meters.  

In a weightless environment, packages and objects drift around the cabin. Yang Hong said that more than 100 items on the ISS have gone missing.  

Veteran US astronaut Scott Kelly made four space flights, lived on the ISS for 340 consecutive days and participated in NASA’s yearlong Twins Study with his brother Mark Kelly, who remained on Earth. In his book Endurance: A Year in Space, a Lifetime of Discovery, Kelly talks about a common problem: losing track of tools, equipment and other items. The ISS inventory system involves the crew scanning barcodes and manually inputting updates, which are monitored by ground control. Occasionally, astronauts come across objects that were missing for years. Even food drifts away from astronauts, only to become an unexpected snack a few days later.  

Tiangong’s inventory system draws lessons from Chinese logistics companies. By scanning QR codes, astronauts can locate cargo and get item information to better manage their inventory. 

Another prominent feature of China’s space station is its regenerative life support system. On previous missions, water and oxygen were transported from Earth. This time, Tiangong will adopt the system used on the ISS: water vapor exhaled by astronauts is collected and their urine is purified to create potable water.  

The system also creates breathable air. Electrolysis of water produces oxygen and hydrogen, and the redundant hydrogen molecules reacts with the carbon dioxide exhaled by astronauts, which produces oxygen.  

Jiao Weixin told NewsChina this is a more “cost-effective way,” as shipments from Earth cost US$20,000 per kilogram.  

Space Power 
One of the main purposes for building the space station is to conduct scientific research. According to the “Handbook of Scientific Experiment Resources of China Space Station” published in April 2019, the space station has 11 major research directives, including space medicine, life science, biotechnology, astronomy and astrophysics, and it is equipped with more than 10 scientific experiment cabinets and seven vacant ones.  

In June 2019, the China Manned Space Engineering Office and the United Nations Office for Outer Space Affairs released nine experimental projects for international cooperation. Many experiments can be carried out under microgravity conditions, such as developing a more accurate atomic clock, which can improve satellite navigation systems, protein crystallization analysis and polypeptide assembly.  

China’s space station will have a large resident – the Sky Survey Space Telescope, which is expected to go into operation around 2024. With its two-meter diameter, the telescope has a resolution ratio equivalent to the Hubble telescope but a field angle more than 200 times greater.  

If it remains in orbit for 10 years, the telescope will observe more than 40 percent of the visible sky. The telescope has 30 sensors with a total resolution of 2.5 billion pixels. Among them, 18 sensors are equipped with filters that can obtain images in specific bands of the electromagnetic spectrum. The remaining 12 observe the seamless spectrum and can obtain spectral data for at least 1,000 celestial bodies with each exposure.  

Jiao Weixin said that the Sky Survey space telescope will be launched separately as an optical module and will run in common orbit with Tiangong. The advantage is that when the telescope needs maintenance, propellant and equipment upgrades, it can dock with the space station and operate independently of other modules.  

In this way, Tiangong serves as a home port for other spacecraft, something the ISS cannot do. Compared with the Hubble telescope, which has been in operation for 30 years and required five servicing missions involving space shuttles carrying astronauts and equipment from Earth, the Sky Survey model is more practical and economical.  

Jiao told NewsChina that as commercial manned space flights are the future, constructing a space station for scientific experiments is of utmost importance. “It’s also crucial to the process of China becoming a strong space power,” he said. 

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