NASA has demonstrated the first trapped-ion space clock in a move that could pave the way for real-time navigation in deep space.
Reported in Nature, the results of more than a year's experimentation have shown the ion optical clock has outperformed current space clocks by an order of magnitude. NASA engineers believe the level of performance shows the approach could be used to enable near-real-time navigation of deep space probes.
Currently, GPS satellites use atomic clocks as part of navigation systems, but there are limits to the approach. They rely on atoms confined by a gas cell to serve as a meter for the clock, but the long-term stability of gas-cell clocks can suffer when the atoms collide with the "walls" of the cell, causing drift. GPS systems get signals from earthbound atomic clocks to correct the instability. But that gets trickier the deeper you go into space. Light signals can sometimes take up to 20 minutes to journey from Earth to Mars so navigators can't make last-minute changes to a spacecraft's path.
Trapped-ion atomic clocks, in which charged atoms are prevented from colliding with walls by an electromagnetic cage, have been around since the early 2000s and are more accurate than earlier approaches to atomic time-keeping, which have been around since the 1950s. NASA's Deep Space Atomic Clock loses one second every 10 million years, as proven in controlled tests on Earth.
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In 2019, NASA launched the trapped-ion clock into orbit around Earth. It was one of 24 satellites on the SpaceX Falcon Heavy Rocket mission.
Eric Burt, a scientist at the California Institute of Technology and principal member of the technical staff at NASA's Jet Propulsion Lab, and colleagues have shown that a year into its operation, its short-term and long-term stability beat current space clock technology by 10 times.
The paper claims that variations in radiation, temperature, and magnetic fields did not seem to limit the performance of the clock, making it suitable for operation in the extreme environment of space. All this despite developing a fault shortly after testing began.
Tests in space confirmed a "drift" of around 10-16 seconds per day, exceeding current space clock performance by up to an order of magnitude.
There is just one catch: time. That is, the current Deep Space Atomic Clock has a predicted lifespan of three to five years, well short of what might be needed for a mission to Mars and beyond.
While promising to extend the durability of the new clock to 10 years or beyond, the authors point out that the development of trapped-ion space clocks could open up applications in one-way navigation for deep space exploration, without the need to phone home. ®