The ISS (pictured here in March 2009) is racing towards completion. In 2013 it will play host to a highly accurate atomic clock.
Credit: NASA
SYDNEY: In 2013 scientists will send an extremely accurate atomic clock into orbit on the International Space Station (ISS). But without a matching clock in Australia, there'll be a big gap in gaining crucial data, an expert warns.
The Atomic Clock Ensemble in Space (ACES) is a European Space Agency (ESA) mission that will test fundamental laws of physics by matching atomic clocks orbiting under microgravity conditions with similar clocks on Earth.
The project, which will run for at least 18 months, will also improve monitoring of Earth systems and wide-field radio astronomy.
Accurate clocks
But while there are many accurate clocks to compare with in the Northern Hemisphere, there is nothing with this sort of precision and accuracy in the Southern Hemisphere, says physicist John Hartnett from the Frequency Standards & Metrology research group at the University of Western Australia in Perth.
Hartnett presented an update on Australian efforts into ACES at the end of September in a talk at the Australian Space Sciences Conference at the University of Sydney. "ACES could answer some of the big questions in physics," he told Cosmos Online.
One such test is of gravitational redshift known as the 'Einstein Effect'. According to Einstein's general theory of relativity, time should slow and the wavelengths of signals received by the ACES clocks should shift towards the red end of the spectrum due to gravitational effects.
Gravity and time
Under ideal conditions, the ticking rate of atomic clocks is only affected by the force of gravity where they are located. On Earth, this gravitational pull varies slightly depending on the mass of the crust below the clock. From space, this gravitational pull is removed.
An Australian ground station hosting an ytterbium ion clock would improve the quality of data from this experiment, as it would enable monitoring of the ACES clocks when the ISS isn't visible from the Northern Hemisphere, which is crucial for several research goals, said Hartnett.
"The experiment could be done with good ground based clocks in the Northern Hemisphere, but you could improve on that by having one in the Southern Hemisphere because you have access to the timing of the orbit [while the space station is overhead], which is very important when you do fundamental physics," he said.
Ytterbium clocks have lately improved accuracy to a standard comparable to the caesium fountain clock upon which the standard of the second is based.
Harnett is pushing to have an ytterbium clock developed by the National Measurement Institute (NMI), accurate to 0.000000000000003 (3 parts in 10 -15) seconds, installed in Perth.
ESA have said they would fund half of the estimated A$1 million cost of building a ground station to track the space station, but more Australian Federal Government funding would be needed, he said.
Dependent on funding
"The final accuracy of the sort of clock we could make in Australia depends on the funding," he said. "We will miss out on some of the science goals of ACES [if we don't have the clock]. This may not sound very important to some people, but I don't think there's a scientific venture that hasn't resulted in a whole lot of spin offs."
Physicist Bruce Warrington from NMI who is working with Hartnett on the ACES goals, said while the NMI's ytterbium clock wasn't as accurate as some of the world's top atomic clocks, it has a high stability in terms of the constancy of its tick.
"Australia is the only Southern Hemisphere partner and the only observing station which will give us a good handle on the [space] clock's performance at less than the full orbit," he said.
Follow Cosmos on Twitter! twitter.com/cosmosmagazine
