Researchers from NASA have reported the results from the first year of operation of the Deep Space Atomic Clock (DSAC), an important technological advancement for incredibly accurate time-keeping in space. The DSAC is 10 times better than current space clocks and had a drift of no more than 4 nanoseconds over 23 days. That means it would take 15.74 million years to be off by a single second.
The technological achievement might, in the near future, be a staple for spacecraft exploring the Solar System. An error of just a fraction of a second might make the difference between getting in orbit around a celestial body or getting lost in the depths of space. The results are published in Nature.
Atomic clocks that have been used on the ground are usually too large and bulky to be sent to space, where every gram matters. Precise measurements are done on Earth, with the spacecraft or satellite in question having a two-way link with ground control to work out what time it is there. This link becomes more complex the further away into space the mission in question is.
One notable exception is GPS satellites, which need multiple atomic clocks on board to guarantee that they are providing the correct information about one’s position on the surface of Earth. In a similar manner, atomic clocks can provide the precise position of a spacecraft in the Solar System but you need to wait for the signal to travel (at the speed of light) from there to Earth and then back again for any automatic decision.
DSAC is set to remedy that issue by being a miniaturized and stable atomic clock that can be integrated easily into current spacecraft. It uses a mercury ion and like all the other atomic clocks it measures time by using some specific vibrations of atoms. The advantage is that it does it better and more efficiently in a more compact space.
“As a general rule, an uncertainty of one nanosecond in time corresponds to a distance uncertainty of about one foot,” co-author Eric Burt, an atomic clock physicist for the mission at JPL, said in a statement. “Some GPS clocks must be updated several times a day to maintain this level of stability, and that means GPS is highly dependent on communication with the ground. The Deep Space Atomic Clock pushes this out to a week or more, thus potentially giving an application like GPS much more autonomy.”
The team also reports that the clock was not shielded against a temperature variation of about 9°C (16.2°F) and radiation and yet performed extremely well. This approach could lead to autonomous navigation of deep space spacecraft and is likely fundamental for crewed missions beyond the Moon.
The current main limitation is the longevity of the instrument. Currently, DSAC is expected to work with no problem for three to five years. The team hopes to extend that to 10 years or more. The DSAC is on board the Orbital Test Bed satellite activated on August 23, 2019. Last week, NASA announced that the DSAC mission would continue through August 2021.
"In the long run, this technology might be revolutionary," said Robert Tjoelker, co-investigator for the DSAC at NASA's Jet Propulsion Laboratory, said in a statement. "Just getting our clock into space and operating well is a big first step. Further refinements towards even longer life and higher stability are already in the works."
NASA plans to fly an upgraded version of this atomic clock on its mission to Venus called VERITAS.
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