Early yesterday morning, NASA launched a SpaceX Falcon Heavy rocket into orbit with a hodgepodge of science missions aboard. One of the most intriguing payloads was a clock, which will tick along for about a year as it circles the planet. But this is no ordinary clock: the Deep Space Atomic Clock is a technology that could make navigating deep space much easier in the future.
Kasandra Brabaw at Space.com reports that most probes sent into the cosmos are tracked from Earth via radio waves, which travel at light speed. A signal is sent from Earth and immediately bounced back to mission control, allowing the probe’s handlers to calculate its exact position based on how long it took the signal to reach them. That process relies on NASA’s Deep Space Network, an array of radio antennas that can only handle so much space traffic at any given moment.
If the probes had clocks stable and precise enough to allow them to chart their own course, however, they could do some of that navigation autonomously, reports Jonathan Amos at the BBC.
“Autonomous onboard navigation means that a spacecraft can perform its own navigation in real-time without waiting for directions to be sent from navigators back here on Earth,” deputy principal investigator Jill Seubert recently told reporters at a press conference. “Self-driving” spacecraft are also a key part of putting humans on Mars. “And with this capability, a human-crewed spacecraft can be delivered safely to a landing site with less uncertainty in their path.”
But even the nicest Rolex won’t cut it in space. Quartz crystals oscillate at a regular frequency when electrical current passes through them, which is why they are used to in clocks to keep track of time. They’re precise enough when it comes to getting up for work or catching a train, but they’re not nearly accurate enough on their own for navigating in deep space. They can lose a full millisecond over the course of six weeks, which would be disastrous for a space probe.
To get the billionth-of-a-second precision needed to fly through the cosmos requires an atomic clock, a gadget that trains its quartz crystal to the oscillations of certain atoms. The electrons around these atoms occupy distinct energy levels, or orbits, and it takes a precise jolt of electricity to cause them to jump to the next energy level. “The fact that the energy difference between these orbits is such a precise and stable value is really the key ingredient for atomic clocks,” Eric Burt, an atomic clock physicist at NASA’s Jet Propulsion Laboratory, says in a press release. “It's the reason atomic clocks can reach a performance level beyond mechanical clocks."
In an atomic clock, the frequency of the quartz oscillator is fine tuned to match the energy needed to pop electrons to a new energy level. When the quartz is vibrating at the right frequency, the electrons will jump to the next energy level. If they don’t, the clock knows the frequency is off and can correct itself, a process that occurs every few seconds.
Currently, most terrestrial atomic clocks are the size of a refrigerator. Enter the Deep Space Atomic Clock, which NASA engineers have been tinkering with for almost 20 years. The gadget, about the size of a toaster, uses charged mercury ions to keep its quartz oscillator true, and loses only about one nanosecond over four days. It would take about 10 million years for the clock to be off by one second, making it about 50 times more stable than the precise clocks used in GPS satellite navigation.
The clock is currently in low Earth orbit and will power on in four to seven weeks. After three to four weeks of operation, researchers will analyze its preliminary performance and will give a final verdict on how well it works in space after it zooms around the planet for about a year.
If the clock is stable enough, according to a NASA statement, it could begin appearing in spacecraft by the 2030’s. Whether this version survives or not, atomic clocks or a similar technology will be critical in future space missions to other worlds.
“The Deep Space Atomic Clock will have the ability to aid in navigation, not just locally but in other planets as well,” Burt says. “One way to think of it is as if we had GPS at other planets.”
Other experiments that went into orbit with the clock include the Green Propellant Infusion Mission ,which is testing a system that uses high-performance, non-toxic space fuel, and the Enhanced Tandem Beacon Experiment, which will explore bubbles in the electrically-charged layers of Earth’s atmosphere that can sometimes interfere with GPS signals.