Super-precise atomic clocks are the future of space travel
“Galactic GPS is actually a real idea.”
Now it’s time for a terrestrial innovation to return the favor and transform life in space.
In a study published this June in the journal Nature, a research team from NASA’s Jet Propulsion Laboratory (JPL) reports on a new design of an atomic clock operating in space, called the Deep Space Atomic Clock. It’s the first atomic clock redesign in decades and has operated aboard General Atomic’s Orbital Test Bed spacecraft since 2019.
The importance of this innovation doesn’t stop just outside Earth’s orbit. Eric Burt, the study’s first author and atomic clock physicist at JPL, tells Inverse that this kind of atomic clock could be used by future space travelers to create a kind of galactic GPS that could take our great-great-grandchildren beyond the outer planets. Through the advancement of atomic clocks, we could have self-driving spacecraft.
“Galactic GPS is actually a real idea,” says Burt. “You can imagine having satellites orbiting the moon and doing GPS on the moon.”
What is an atomic clock?
Invented back in 1948, an atomic clock really isn’t all that different from the kind of clock you have hung on your wall or even the sundial you might have in your garden, Burt explains. All clocks have essentially two elements: an oscillator and a counter.
In your wrist-watch or wall clock, the oscillator is a piece of quartz rock that vibrates rhythmically when under an electric voltage. The time it takes this piece of quartz to oscillate and return to its starting point is equivalent to one second, Burt says.
While standard quartz clocks are pretty reliable when it comes to their measurement of time on Earth, they do suffer from a problem with “drift.” In other words, over time these clocks become less and less precise. Losing a few milliseconds of accuracy on your wristwatch won’t make you late on the way to work, but it can have a much bigger effect on fast-moving objects like spacecraft that risk disaster if they don’t nail their landing or orbit insertion.
In an atomic clock, like the one Burt and colleagues sent to space in 2019, the quartz is supplemented with something called a trapped-ion. These atoms can be trapped using specially coated chamber walls or an electromagnetic field.
They are so precise that a clock like the Deep Space Atomic Clock is estimated to take 10 million years to lose 1 second of accuracy.
Rugged enough to survive space travel while also stable enough to keep good time once it gets there (thanks to mercury atoms held very still by an electromagnetic field,) Burt and colleagues found that the Deep Atomic Space Clock beat the accuracy of existing atomic space clocks ten times over.
How an atomic clock works
Here’s how that tiny trapped ion makes such a difference:
- The frequency of a synthesizer referenced to a quartz oscillator is applied to a collection of mercury atoms. This synthesizer helps derive the atomic transition frequency of the atoms.
- If the quartz oscillator vibrates correctly, the mercury atom’s electrons will begin jumping between discreet and stable energy levels
- How many atoms actually respond to the synthesizer frequency helps the clock make a correction to stay on course to avoid drift
- This type of frequency correction is applied every few seconds to the Deep Space Atomic Clock
For positioning, typical satellite-bound atomic clocks will then ping signals back and forth between space and large, Earth-bound atomic clocks on the ground.
By calculating the time delay between pings and the location of the transmitters and receivers the satellite can precisely triangulate positions on Earth. Atomic clocks are already used to control the wave frequency of television broadcasts, in traditional GPS, and as the standard for international timekeeping.
Scientists are hopeful that the Deep Space Atomic Clock will enable autonomous navigation to distant destinations like Mars — meaning that, in the future, there will very likely be self-driving spacecraft.
“... having a real-time estimate of what your trajectory is can really narrow down or make the landing more precise.”
In the Nature study, Burt and colleagues report that the Deep Space Atomic Clock is able to do something called “one-way navigation.” This means it could perform real-time trajectory analysis without having to double-check with the Earth clocks along the way.
“This new method, which is just now being demonstrated using this technology, is called ‘one way’ because it just takes the signal going up and that's it,” says Burt. “A computer on board is able to do the same calculation that’s done on Earth, but it's doing it in real-time.”
With this one-way navigation, future space crews could calculate their distance from distant planets in real-time instead of waiting up to an hour for Earth to ping the information to them, Burt explains.
Atomic clocks and galactic GPS
More than just a feather in their cap, this achievement could also open the door for a new kind of GPS system altogether: interplanetary GPS.
As space travelers explore further and further beyond Earth’s orbit, having an accurate idea of exactly where they are in our solar system will be crucial for the success of both crewed and robotic missions in the future, Burt explains.
“When you're inserting in an orbit where there's an atmosphere that can perturb your trajectory and make it somewhat a little less predictable, having a real-time estimate of what your trajectory is can really narrow down or make the landing more precise,” Burt says. “That’s the big advantage.”
This kind of GPS would use atomic clocks built into spacecraft to help probes fly safely into Venus’ atmosphere or help human crews set up a new colony on the moon.
And while travel beyond our solar system with such a system may just be unlikely right now, Burt wouldn’t necessarily rule it out either.
“It’s kind of science fiction to imagine a single GPS system that would give you position everywhere on greater than a solar system scale,” Burt says. “You probably would be transporting your own system with you and combining it with knowledge and maps of other star systems. That's pretty speculative.”
The Deep Space Atomic Clock mission will conclude in August, but that doesn’t mean the work is done yet: the Deep Space Atomic Clock 2 will fly on the VERITAS mission to Venus.
Editor's note: This article was updated on July 8th to more precisely explain the difference between a quartz oscillator and a synthesizer referenced to a quartz oscillator.