Since the Soviet Union launched the first Salyut space station 50 years ago, humans have lived in a total of 11 such objects in low-Earth orbit. China will soon add another one to this list. With the launch of the China Space Station (CSS) core module in late April, the culmination of the country’s government project originally conceived in 1992 is finally entering the construction phase.
After the main module reaches space, China is planning at least 10 more launches of other main modules, as well as manned and cargo missions, to complete assembly of the station by the end of 2022. By this time, CSS will join the International Space Station (ISS) as the only fully operational space stations in orbit.
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Putting it all together
The T-shaped 100-ton CSS will consist of three main modules: an 18-meter-long main module called Tianhe (“Heaven’s Harmony”), and two 14.4-meter-long experimental modules called Ventian (“Search for Heaven”) and Mengtian ( “Dreams of Heaven”), which will be permanently attached to either side of the core. As a command and control center, Tianhe Station can accommodate three astronauts for up to six months. Visiting astronauts and cargo spacecraft will connect to the main module from opposite ends. Both he and Wentian are equipped with robotic arms outside, and Mengtian has an airlock for maintenance and repair experiments installed outside the station. Tianhe has a total of five docking ports, which means an additional module can be added for future expansion. The station is designed to operate for over 10 years.
The mass of CSS is less than a quarter of the mass of the ISS, the largest and most expensive human-made structure in space, jointly built by 15 countries. “We weren’t going to compete with the ISS on a scale,” says Gu Yidong, chief scientist for the China Manned Space Program. Instead, the three-module configuration is “based on China’s scientific experimentation needs” and “we consider a reasonable size for the sake of economic efficiency.”
To develop CSS, China followed a three-step strategy: first they built crewed spaceships (missions to Shenzhou), then mini-space stations (Tiangong-1 and 2), and then soon launched a multi-module station. The CSS construction was officially approved in 2010. Although China’s heavy-lift rocket failed at launch in 2017, delaying Tianhe’s launch by more than a year, the country’s space leaders hope to stick to the goal of completing the space station in 2022 with intensive launches over the next two years.
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Domestic and international experiments
The CSS will contain 14 refrigerator-sized science experiment racks and several general-purpose racks to provide power, data, cooling and other services for a variety of research projects. There will also be more than 50 docking points for experiments that will be set up outside the station to study how materials react to the effects of space. Science inside and outside will include space physiology, life science, fluid physics, materials science, astronomy, and Earth observation. According to Gu, about 100 experiments have been selected so far from more than 800 domestic proposals. Some of them may start collecting data as early as next year.
For example, the station will use the world’s most accurate clocks and coldest atoms to support basic research in general relativity and quantum physics. CSS clocks are designed to achieve incredibly low levels of volatility, with a margin of error of just one second every three billion years. The rack for experiments with ultracold atoms can cool atoms down to 10-10 kelvin, the lowest temperature achievable with modern technology. Some of the racks will be the first of their kind on the space station, including one dedicated to studying phase transitions between liquid and gas states of matter, because these processes become more pronounced in microgravity conditions. This research could, for example, help develop more compact and efficient cooling devices for spacecraft and even laptops.
The station will also reserve space and resources for a number of international experiments. Tricia Laroz, a medical researcher at the University of Oslo, is leading the 31-day Tumors in Space Experiment, which tests whether weightlessness can slow or stop cancer growth, among other things. As one of nine international projects selected by the China Manned Space Agency (CMSA) and the United Nations Office for Outer Space Affairs (UNOOSA), the mission will use three-dimensional stem cell organoids, or “mini colons,” grown from cancer cells. and healthy colon tissues of the same patient to study how microgravity affects DNA mutations. “All previous experiments to combat cancer in space have used two-dimensional cell lines,” says Laroz. “In comparison, organelles mimic the structure and function of an organ and are the most physiologically significant bioassays to use.”
Call for cooperation
CSS could expect the company a year or two after its completion: China plans to launch a Hubble-sized telescope that will operate in the same orbit a few hundred kilometers away. As part of CSS, the China Sky Observing Telescope (also called Xuntian) will have a field of view 300 times that of the Hubble and will be used for a wide range of scientific research in the near ultraviolet and optical wavelengths. The observatory will explore cosmology, the large-scale structure of matter in the Universe, galaxy and stellar science, as well as dark matter and dark energy. It is designed to dock with the space station for maintenance when needed, offering a simple, cost-effective and “best way to get astronauts to keep the telescope up and running,” Gu says.
Xuntian has the same projects and goals as the European Space Agency’s Euclid mission and NASA’s Nancy Grace space telescope in Rome, which will be launched in the coming years, but will operate in additional wavebands. Gu believes that collaboration between the three telescopes and the sharing of observational data will lead to a deeper understanding of the universe and fundamental physics.
China welcomes the collaboration of scientists from around the world on CSS, Gu said. The CMSA-UNOOSA collaboration will soon announce a second call for proposals for international experiments. Scientists can also apply through institutional partnerships to access space station resources. However, it is unclear what level of international cooperation CSS will gain, due to geopolitical obstacles. US law severely restricts direct collaboration between NASA scientists and China. In Europe, agency pressure has also made it difficult to obtain funding for projects related to China’s space program. Laros notes that she and her colleagues have faced “an unexpected level of indecision” with CSS-related grant applications. This is disappointing, she said, because cancer knows no boundaries and the search for more effective treatments benefits everyone in every country on earth. “When will we stop looking at our differences and start focusing on our similarities?” Laros asks.
Ling Xin writes about physics, astronomy, space travel and related fields. More of her work can be found at lingxinwrites.com. She is originally from Beijing and now lives in Ohio.