Deep Space Atomic Clock sets record in 1st test run

An atomic clock designed to change the way we navigate in space has succeeded in its first space-based test run. Researchers described the test and its results in a new paper published online this week (June 30, 2021) in the peer-reviewed journal Nature. Here on Earth, GPS satellites carry atomic clocks to help us navigate to our destinations without, for example, calling back home for instructions on which roads to take. Likewise, the Deep Space Atomic Clock will give robotic space probes and future human travelers more autonomy – more self-governance – when navigating at distances beyond Earth’s moon.

NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, is managing the project. As NASA explained in a statement:

… Spacecraft that venture beyond our moon rely on communication with ground stations on Earth to figure out where they are and where they’re going.

But space-based atomic clocks will change that, once researchers work out all the bugs. One major issue has been space-based atomic clocks’ ability to measure time consistently over long periods. NASA said:

Known as ‘stability,’ this feature also impacts the operation of GPS satellites that help people navigate on Earth …

And NASA said:

‘Stability’ refers to how consistently a clock measures a unit of time. Its measurement of the length of a second, for example, needs to be the same (to better than a billionth of a second) over days and weeks.

In the new study, researchers report that the Deep Space Atomic Clock has been operating aboard General Atomic’s Orbital Test Bed spacecraft since June 2019. NASA said:

The new study reports that the mission team has set a new record for long-term atomic clock stability in space, reaching more than 10 times the stability of current space-based atomic clocks, including those on GPS satellites.

A metallic, squarish box with wires visible through small openings.
NASA said its Deep Space Atomic Clock could “revolutionize” deep space navigation. A compact design is a key requirement for the technology demonstration. The complete hardware package, shown here, is only about 10 inches (25 cm) on each side. Image via NASA.

How do we navigate in space?

At present, spacecraft controllers help a craft navigate by sending a signal to the craft, which bounces the signal back. Refrigerator-sized atomic clocks on the ground measure precisely how long the signal took to travel back and forth. Since the signals travel at a known speed – the speed of light – scientists can then calculate precisely how far the spacecraft has traveled. You might have learned this formula in school. Distance = speed x time?

But space – even the space inside our own solar system – is vast. NASA said:

… for robots on Mars or more distant destinations, waiting for the signals to make the trip can quickly add up to tens of minutes or even hours.

Now imagine if a spacecraft were carrying its own atomic clock. In that case, the spacecraft could receive a signal from Earth and quickly calculate its own current positions and direction of travel. So you might see that NASA’s Deep Space Atomic Clock will give future robotic and human explorers more autonomy. Future craft carrying these clocks will be able to navigate on their own.

That’s where stability comes in

NASA explained that:

… the clocks would have to be highly stable. GPS satellites carry atomic clocks to help us get to our destinations on Earth, but those clocks require updates several times a day to maintain the necessary level of stability. Deep space missions would require more stable space-based clocks.

NASA explained that all atomic clocks have some degree of instability. This leads to an offset in the clock’s time versus the actual time. If not corrected, NASA said:

… the offset, while miniscule, increases rapidly, and with spacecraft navigation, even a tiny offset could have drastic effects.

One of the key goals of the Deep Space Atomic Clock mission was to measure the clock’s stability over longer and longer periods, to see how it changes with time. In the new paper, the team reports a level of stability that leads to a time deviation of less than four nanoseconds after more than 20 days of operation.

That’s reliable enough for use in future missions. Eric Burt, an atomic clock physicist for the mission at JPL and co-author of the new paper, added:

As a general rule, an uncertainty of one nanosecond in time corresponds to a distance uncertainty of about one foot [one-third m]. 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 mission continues

JPL in Southern California has managed the Deep Space Atomic Clock project since 2019. The Deep Space Atomic Clock has been working onboard the General Atomics Orbital Test Bed in orbit around Earth. According to NASA-JPL, the progress of this mission doesn’t represent an improvement of the clock itself but an improvement in its ability to measure time and space. And proponents of the project believe additional data can further improve it.

The project will conclude in August of this year, but will be followed by the Deep Space Atomic Clock-2. That will serve as an advanced version of the timekeeper and will fly on the VERITAS mission to Venus.

This demonstration may potentially impact GPS satellite operations like the ones essential for our day-to-day navigation on Earth. Even self-driving spaceships could be made possible, as soon as the mid-2020s. Most of us live a life so accustomed to technology that we easily forget what feats make everyday tools like a GPS app so accessible. To some, this project is an exciting reminder.

Robert Tjoelker, co-investigator for the Deep Space Atomic Clock at JPL, said:

In the long run, this technology might be revolutionary. 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.

A small, boxy, blue and white spacecraft floating in space above Earth with the moon behind it.
Artist’s concept of the Deep Space Atomic Clock onboard the General Atomics Orbital Test Bed spacecraft in Earth orbit. Image via General Atomics Electromagnetic Systems/ NASA.

Bottom line: NASA’s Deep Space Atomic Clock has outperformed all other clocks in space during its first year in orbit around Earth. The clock is at least 10 times more stable than those used on GPS satellites: a new record, according to researchers.

Source: Demonstration of a trapped-ion atomic clock in space


July 2, 2021

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