Friday , January 22 2021

Atomic Clocks Explained: NASA Set to Launch a Deep Space Timekeeper Monday

NASA is poised to launch an incredible new atomic clock into orbit in a Falcon Heavy Tomorrow (June 24) on a technology demonstration mission that could transform the way humans explore space.

O Deep Space Atomic Clock, developed by the NASA Jet Propulsion Laboratory, is a ready upgrade to the space for atomic clocks we use here on Earth and to clocks that already fly on satellites such as those that provide GPS.

Ideally, this new atomic clock will make spacecraft navigation to distant objects in space – in trip to Mars, for example – more autonomous, NASA said in a statement. The precision in measuring the position of the spacecraft that scientists hope to achieve with the Deep Space Atomic Clock will allow spacecraft traveling in deep space to act on their own without much communication with Earth. It would be a major improvement on how spacecraft are currently navigated, NASA said.

Related: This is what 2 dozen satellites look packaged for launch in a SpaceX Falcon Heavy

But how does this work?

Astronomers already use clocks to navigate space. They send a signal to the spacecraft, which sends it back to Earth. The round trip time tells scientists how far the spacecraft from Earth is. This is because the signal is traveling in the speed of lightSo, armed with the time it took to go to the spacecraft and back, finding distance is just a simple calculation away. By sending several signals over time, scientists can calculate the trajectory of a spacecraft – both where it was and where it is going.

But to know the location of a spacecraft within a small margin of error, astronomers need very accurate clocks that can measure billionths of a second, according to NASA. They also need extremely stable watches. "Stability" here refers to how consistently a clock measures a unit of time. Although you find that watches always measure the same amount of time as a "second", clocks tend to deviate and slowly mark more and more times as "second." To measure spacecraft locations in the far space, astronomers need their atomic clocks to be consistent more than a billionth of a second over days and weeks.

Modern clocks, from those we use on our wrists to those used in satellites, most often, keep time using a quartz crystal oscillator. These take advantage of the fact that quartz crystals vibrate at a precise frequency when the voltage is applied to them, NASA said in the statement. The vibrations act like the pendulum of a pendulum clock.

But by the standards of space navigation, quartz crystal watches are not very stable. After six weeks, they can be turned off for an entire millisecond, which translates into the speed of light for 300 kilometers. That big mistake would have a huge impact on measuring the position of a fast spacecraft, NASA said.

Atomic clocks combine quartz crystal oscillators with certain types of atoms to create better stability. NASA Deep Space Atomic Clock will use mercury atoms and be off in less than one nanosecond after four days and less than one microsecond after 10 years. It would take 10 million years for the clock to be wrong for a whole second, according to NASA.

Related: A NASA atomic clock on SpaceX's Next Falcon Heavy will pioneer deep space travel technology

It is perhaps not surprising that atomic clocks take advantage of the structure of atoms, composed of a nucleus of protons and neutrons surrounded by electrons. The atoms of each element have a distinct structure, with a different number of protons in the nucleus. While the number of electrons of each type of atom can vary, electrons occupy distinct levels of energy, and a shock of exactly the right amount of energy can cause an electron to jump to a higher level of energy around the nucleus.

The energy required to make an electron make this jump is unique to each element and consistent to all atoms of that element. "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, JPL's atomic clock physicist, said in a statement. "It's the reason why atomic clocks can reach a level of performance beyond mechanical clocks."

In essence, atomic clocks can be corrected. In an atomic clock, the frequency of the quartz oscillator is transformed into the frequency that is applied to a collection of atoms of a specific element. If the frequency is correct, it will cause many electrons in the atoms to skip energy levels. But if it is not, fewer electrons will jump. This tells the clock that the quartz oscillator is out of frequency and how much to correct it. At the Deep Space Atomic Clock, this correction is calculated and applied to the quartz oscillator every few seconds.

But that's not all that makes the Deep Space Atomic Clock special. This watch uses not only mercury atoms, it also uses charged mercury ions.

Because ions are electrically charged atoms, they may be contained in an electromagnetic "trap". This prevents atoms from interacting with the walls of a vacuum chamber, a common problem with the neutral atoms used in regular atomic clocks. When interacting with vacuum walls, environmental changes, such as temperature, can cause changes in the atoms themselves and lead to frequency errors.

The Deep Space Atomic Clock will not be subject to such environmental changes, according to NASA, and so it will be 50 times more stable than the clocks used in GPS satellites. Once the clock is released on Monday, scientists will be able to begin testing the accuracy of the clock as it passes the days, then the months in orbit.

The Deep Space Atomic Clock will be released from the Kennedy Space Center in Florida on a SpaceX Falcon Heavy rocket as one of the two dozen loads. The 4 o'clock launch window opens at 11:30 p.m. EDT (0330 June 25, GMT); visit tomorrow for full launch coverage.

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