NASA's most accurate atomic clock to be tested on mission to Venus

The extremely precise atomic clocks are used in particular for applications such as GPS systems, requiring very precise calculations of distances based on the travel time of the waves emitted and received by the satellites. NASA, which recently designed its most accurate atomic clock, is preparing to test it on a mission to Venus. The clock, the first to be used in a GPS-type technology intended for deep space, is currently in the test phase in orbit around the Earth.

Atomic clocks work by measuring the radiation emitted by electrons as they move from a lower orbit to an upper orbit around atoms. They are currently used in spacecraft, but atoms can collide with the walls of the vessel that contains them, affecting accuracy.

NASA's Deep Space Atomic Clock (abbreviated DSAC), 25 times more accurate than existing space atomic clocks, solves this problem by using mercury ions as timepieces, which carry a charge and can therefore be kept away from the wall of the clock by an electromagnetic field.

NASA launched the DSAC in 2019 to test its long-term stability and reliability in orbit, and has now published research results showing that its accuracy far exceeds any other clock in space. Eric Burt of NASA's Jet Propulsion Laboratory in California and his colleagues found that the DSAC only drifted by 4 nanoseconds overall in 23 days. Current space atomic clocks, such as those used in GPS satellites, would show a drift of about 100 nanoseconds over the same period.

Real-time space probe navigation soon possible

Lowering the error rate, according to Burt, is critical to achieving accurate navigation. Many space missions currently use atomic clocks the size of a coin. These clocks are very precise but consume a lot of energy, and their signals take longer to arrive as a spacecraft moves away from Earth.

At the same time, current atomic clocks miniaturized for use in space are significantly less precise than what is necessary to maintain precise autonomous navigation. A more accurate clock on board a spacecraft would allow it to calculate its own path instead of waiting for signals from Earth.

"This level of performance of space clocks will allow unidirectional navigation in which signal propagation times will be measured in situ, which will make possible near real-time navigation of space probes," the researchers write in their paper.

A DSAC will be included in NASA's recently announced VERITAS mission to Venus. This ship will include its own chronometer, based on a standard quartz clock, but will carry a DSAC as a test bed for future missions. The team is also working on a version of the atomic clock that could fit into the space occupied by the less precise clocks currently found in GPS satellites.


Burt, E.A., Prestage, J.D., Tjoelker, R.L. et al. Demonstration of a trapped-ion atomic clock in space. Nature 595, 43–47 (2021).

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