# What Is an Atomic Clock? – NASA

What Is the Definition of an Atomic Clock?

The time is running out: The intended launch date for a technology demonstration that could change the way humans explore space is June 24, 2019. The Deep Space Atomic Clock, developed by NASA’s Jet Propulsion Laboratory in Pasadena, California, is a significant enhancement over satellite-based atomic clocks that, for example, enable GPS on your phone.

In the end, this new technology may allow spaceships to navigate to faraway regions such as Mars on their own. But, first and foremost, what is an atomic clock? What makes the Deep Space Atomic Clock unique is how it is employed in space navigation. Continue reading to find out all of the answers.Read more: NASA’s Deep Space Atomic Clock: Five Things to Know What is the purpose of using clocks to navigate in space?

Navigators give a signal to a spacecraft to estimate its distance from Earth, which the spacecraft subsequently returns to Earth. Because the signal travels at a known speed, the time it takes to complete the two-way voyage indicates the spacecraft’s distance from Earth (the speed of light).

While it may appear difficult, most of us employ this notion on a daily basis. It’s possible that the grocery store is a 30-minute walk from your home. You can calculate the distance to the store if you know you can walk a mile in 20 minutes.

Navigators can compute a spacecraft’s trajectory: where it is and where it is going, by transmitting many signals and obtaining several measurements over time. Quartz crystal oscillators are utilised in almost all modern clocks, from wristwatches to satellites. When voltage is given to quartz crystals, they vibrate at a particular frequency, which is used in these devices. The crystal’s vibrations function like a grandfather clock’s pendulum, keeping track of how much time has passed.

Navigators need clocks with precision time resolution — clocks that can measure billionths of a second — to know the spacecraft’s position to within a metre.

Clocks that are exceptionally stable are also required by navigators. “Stability” relates to how consistently a clock counts a unit of time; for example, the length of a second must be consistent across days and weeks (to better than a billionth of a second).

What are the connections between atoms and clocks?

Quartz crystal clocks aren’t extremely stable by space navigation standards. Even the best-performing quartz oscillators might be off by a millisecond after only an hour (one billionth of a second). They might be inaccurate by a whole millisecond (one thousandth of a second), or 185 miles, after six weeks (300 kilometers). This would have a significant impact on determining the position of a rapidly moving spacecraft.

To attain higher stability, atomic clocks combine a quartz crystal oscillator with an ensemble of atoms. After four days, NASA’s Deep Space Atomic Clock will be off by less than a nanosecond, and after ten years, it will be off by less than a microsecond (one millionth of a second). This is the equivalent of being one second off every ten million years. The frequency of the quartz oscillator is converted into a frequency that is applied to a group of atoms in an atomic clock.

Many electrons in the atoms will shift energy levels if the derived frequency is correct. There will be considerably fewer electrons jumping if the frequency is incorrect. This will establish if and how much the quartz oscillator is off-frequency. The quartz oscillator can then be steered back to the correct frequency using a “correction” established by the atoms. The Deep Space Atomic Clock calculates and applies this form of correction to the quartz oscillator every few seconds.

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What makes the Deep Space Atomic Clock special?

Onboard the GPS satellites that circle the Earth, atomic clocks are employed, although even they need to be updated twice a day to rectify the clocks’ natural drift. Those updates are provided by more stable atomic clocks on the ground, which are huge (typically the size of a refrigerator) and not built to withstand the physical demands of space travel.

NASA’s Deep Space Atomic Clock is designed to be the most stable atomic clock ever flown in space, up to 50 times more reliable than the atomic clocks on GPS satellites. Mercury ions are used to create this stability.

Ions are atoms that are not electrically neutral but have a net electric charge. Atoms are contained in a vacuum chamber in any atomic clock, and in certain of those clocks, atoms interact with the vacuum chamber walls. Changes in the environment, such as temperature, will trigger corresponding changes in the atoms, resulting in frequency inaccuracies. Because the mercury ions have an electric charge, they can be trapped in an electromagnetic “trap” to prevent this interaction, allowing the Deep Space Atomic Clock to achieve a new degree of precision.

Such precision makes autonomous navigation possible with minimum communication to and from Earth for missions travelling to distant destinations like Mars or other planets, which is a big improvement over how spacecraft are currently navigated.