NASA Activates a New Atomic Clock

Precise radio navigation -- using radio frequencies to determine position -- is vital to the success of a range of deep-space exploration missions. The Deep Space Atomic Clock project will fly and validate a miniaturized, ultra-precise, mercury-ion atomic clock that is orders of magnitude more stable than today’s best navigation clocks, forever changing the way we conduct deep-space navigation. The DSAC project, managed for NASA's Space Technology Mission Directorate by NASA's Jet Propulsion Laboratory, built a demonstration unit and payload that was launched into Earth orbit in June 2019, at which time the payload will be operated for at least a year to demonstrate its functionality and utility for one-way-based navigation. An atomic clock that could pave the way for autonomous deep space travel was successfully activated last week and is ready to begin its year-long tech demo, the mission team confirmed on Friday, Aug. 23, 2019. Launched in June, NASA's Deep Space Atomic Clock is a critical step toward enabling spacecraft to safely navigate themselves in deep space rather than rely on the time-consuming process of receiving directions from Earth.

To determine a spacecraft's distance from Earth, navigators send a signal to the spacecraft, which then returns it to Earth. The time the signal requires to make that two-way journey reveals the spacecraft's distance from Earth, because the signal travels at a known speed (the speed of light). While it may sound complicated, most of us use this concept every day. The grocery store might be a 30-minute walk from your house. If you know you can walk about a mile in 20 minutes, then you can calculate the distance to the store. By sending multiple signals and taking many measurements over time, navigators can calculate a spacecraft's trajectory: where it is and where it's headed. Most modern clocks, from wristwatches to those used on satellites, keep time using a quartz crystal oscillator. These devices take advantage of the fact that quartz crystals vibrate at a precise frequency when voltage is applied to them. The vibrations of the crystal act like the pendulum of a grandfather clock, ticking off how much time has passed.

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https://www.jpl.nasa.gov/news/news.php?feature=7430