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Work Underway on Deep Space Atomic Clock

(Source: NASA)

Baseball legend, Yogi Berra, made this timeless quip:

You’ve got to be very careful if you don’t know where you are going because you might not get there.

Over the decades, NASA has been a milestone-making agency, known worldwide for precision “get there” navigation of spacecraft to distant worlds. But the pursuit of even more accuracy to carry out on-the-spot landings on Mars, or to dispatch a probe to an ultra-precise touchdown on an asteroid, is on the agenda for NASA’s Space Technology Program.

NASA is preparing to fly a small, low-mass Deep Space Atomic Clock, or DSAC–a next-generation technology that can greatly improve deep space navigation and radio science.

While cesium and rubidium atomic clocks are in use on satellites in Earth orbit–specifically in the Global Positioning System (GPS) satellite constellation–there are no atomic clocks onboard interplanetary spacecraft.

“What this project is really about is changing the way we do our navigation,” says Todd Ely, principal investigator of the Deep Space Atomic Clock Technology Demonstration at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We’re building an atomic clock that is a very small package, just a handful of kilograms in size.”

The DSAC is being readied for launch into Earth’s orbit in 2015. This demonstration mission would validate the very heart of the hardware: a miniaturized mercury-ion atomic clock.

Timekeeping Stability

Ely points out that the key to the DSAC is producing an extremely stable frequency and time source.

For example, a person’s wristwatch that uses a quartz crystal, there’s a vibration that’s resonate for that particular crystal. A quartz watch runs by a battery-powered electronic movement that uses a low-frequency tuning fork. That tuning fork builds oscillation through an electrical current to create pulses that run the timepiece.

An atomic clock takes the intrinsic stability of an atomic transition from one energy state to another. The timekeeping advantage that atomic clocks have over quartz clocks is in long-term frequency stability. By measuring the transition of atoms as they move back and forth between two energy levels, atomic clocks provide an absolute reference for frequency and time.

Thanks to more than two decades of dedicated work at JPL, a space-rated, advanced prototype mercury-ion trap atomic clock is nearing its first test flight. Flying as a hosted payload on another spacecraft, the year-long investigation will make use of GPS signals to demonstrate precision orbit determination and confirm the clock’s overall performance.

Ely adds that by flying DSAC on future NASA missions, the device can increase navigation and radio science data quantity by two to three times, as well as improve data quality by up to 10 times.

In addition, the DSAC can provide a cost-savings down here on Earth.

The one-way downlink communications enabled by the onboard atomic clock uses the existing Deep Space Network more efficiently than the current two-way system. Therefore, it expands the network’s capacity without adding any new antennas and their associated costs.

atomic clock

Future Missions

Possible DSAC-assigned duties in the future include enabling pinpoint landings on planets, such as Mars; executing gravity mapping of planetary bodies; and providing an onboard frequency reference for both occultation measurements and solar system relativity tests.

It also has been proposed to land and operate a DSAC on an Earth-approaching asteroid. Doing so would enable tracking the space rock to determine with good statistics if the object could be a threat to our planet, Ely points out.

“Obviously, a one year experiment of the DSAC in Earth orbit isn’t enough to prove out a long-life capability of the clock,” Ely concludes. “But because of some of the clock’s design features–there are no consumables, we are radiation tolerant–we expect the clock to have a long-life potential which makes it infusible into a number of deep space missions.”

“Many NASA missions takes years of planning and development to ensure their success, and every NASA mission has been made possible by pushing the technology envelope,” explains Dr. Mason Peck, NASA’s Chief Technologist. “America expects boldness from NASA. We are now returning to our innovation roots, taking the long-term view of technological advancement that is essential for accomplishing our missions. America expects no less.”
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