The clock is ticking for the world’s most accurate working time piece, the NIST-F2 atomic clock operated by America’s National Institute of Standards and Technology in Boulder, Colorado.
And fittingly, the challenge is coming from the country that invented the mechanical clock almost 1,300 years ago – China.
The US clock is a large, heavy machine, standing more than 2.5 metres high, with support facilities filling an entire room, but it is so accurate that it would lose just one second in 300 million years.
In contrast, the Cold Atomic Clock in Space (Cacs) recently developed by researchers in Shanghai can easily be lifted by two people and would fit comfortably in the boot of a car. But it is expected to be three times more accurate than NIST-F2, losing only a second in one billion years.
It will be able to beat the US clock because it will have escaped the negative grip of gravity.
“It is the world’s first cold atomic clock to operate in space ... it will have military and civilian applications,” said Professor Xu Zhen, a scientist involved with the Cacs project.
China’s Beidou satellite navigation network currently provides less precise guidance than the US GPS system, but Xu said that using Cacs as a time reference in space would give a “significant boost” to Beidou’s performance.
Cacs, several thousand times more accurate than the clocks used in GPS satellites, will start its journey when Tiangong-2, China’s second space laboratory, is launched from the Jiuquan Satellite Launch Centre in Inner Mongolia Thursday night . Other instruments on Tiangong-2, some of them world firsts, include the Gamma-ray Burst Polarimeter (Polar), capable of studying the most powerful explosions in the universe, quantum communication devices, and a “forge” to generate extremely high heat for the creation of new materials such as armour in a microgravity environment. A “bodyguard” satellite will fly around the space lab to protect it from potentially deadly collisions with space debris.
Scientists said the launch of Tiangong-2 would mark China’s transition from a follower in space research to a pioneer.
Xu, a researcher with the Chinese Academy of Sciences’ Shanghai Institute of Optics and Fine Mechanics, said the space atomic clock project was a good example of that transition.
The idea of sending an atomic clock into space was first proposed by European scientists more than 20 years ago. But the European Space Agency’s Atomic Clock Ensemble in Space project (Aces) has faced numerous delays and, according to its latest schedule, won’t be mounted on the International Space Station until next year.
Scientists in the United States also started their own space cold atomic clock project but it was cancelled due to federal government budget cuts, prompting some of the American researchers to switch to the European project.
An atomic clock runs on the principle that electrons orbiting the nucleus of an atom “leap” from one energy state to another under certain frequencies of microwave radiation. The atom could therefore serve as an extremely reliable “timekeeper” when generating and maintaining microwaves at a stable frequency for time reference.
The official definition of a second, for instance, is 9,192,631,770 cycles of the microwave that would cause an atom of the element caesium to swing between two energy states.
A cold atomic clock is more accurate than a normal – or “hot” – atomic clock because it uses a laser to slow down the atom from a speed of several hundred metres per second to just one centimetre per second. Because the atom is the timekeeper, a slower moving one lessens the likelihood of counting errors and results in a more accurate clock.
But atoms are also “distracted” by gravity, and the low level of gravity in space should be able to further improve the accuracy of cold atomic clocks.
In a paper last year, the Chinese team said that the ground prototype of Cacs had caught up with the performance of Pharao, the competing clock in Europe’s Aces project.
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