China’s space station prepares for new frontiers of science with launch of Mengtian module
- Once docked with Tiangong station, module will house experiments in combustion, heat transfer and fluid physics under microgravity
- Ultracold atoms physics cabin aims to use lasers to cool atoms to lowest temperature ever achieved by humans
Mengtian is an 18-metre (59ft) long, 22-tonne module designed mainly for scientific experiments. It is the third and final major component of the Tiangong space station. The module is expected to lift off on October 31, although an official launch date is yet to be announced.
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Mengtian will carry a number of world-leading physics facilities into orbit, including one that can create the coldest matter in the universe.
The ultracold atoms physics cabin, which will be among the eight fridge-sized research cabins on board, aims to use lasers to cool atoms to 10 picokelvins. That is 100-billionth of a degree above absolute zero (−273.15 Celsius) – the lowest temperature ever achieved by humans – said the cabin’s chief scientist Liu Liang, of the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences.
If successful, it will surpass Nasa’s cold atom lab, a similar experiment on the International Space Station (ISS), about tenfold, according to a presentation by Liu at the National Space Science Assembly in Taiyuan in August.
Ultracold atoms have wide applications, from quantum computing to the world’s most accurate clocks. They are also an ideal tool for studying fundamental physics. For instance, they allow scientists to observe a fifth state of matter called Bose-Einstein condensate.
First predicted by Albert Einstein in the 1920s, Bose-Einstein condensate is a group of atoms chilled to near absolute zero, when their energies become so low that they stop moving and clump together to behave like a “super-atom”.
Scientists have used pairs of lasers pointing in opposite directions to trap and cool atoms. Every time the atoms absorb and release light particles from the laser beams, they lose some of their energy. After thousands of such impacts, the atoms come to within a few billionths of a degree above absolute zero.
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However, cooling atoms on Earth is tricky. They are constantly pulled downward by gravity, and will not stay put to let lasers do their job, a problem that does not exist in a microgravity environment.
On Tiangong, rubidium or potassium atoms will be chilled by more than two dozen lasers in multiple steps. The ultracold atoms will form gas bubbles, some as big as 1 centimetre across, to allow astronauts and scientists to observe their behaviour and interactions with the naked eye.
A major difference between the cold atom experiments on Tiangong and the ISS is that the Chinese facility uses three dimensional lasers to produce ultracold gas bubbles while the US device features an atom chip which is used to generate magnetic fields and manipulate the bubbles, Liu said.
While 10 picokelvins is a challenging goal, tests on the ground had shown stable and replicable results, according to Gu Yidong, chief scientist of China’s manned space programme, who spoke at the same meeting.
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The module is also equipped with cabins to study combustion, heat transfer and fluid physics under microgravity, as well as exterior facilities which can support experiments on how materials and plants react to space radiation.
