Todd Ely, an astronautical engineer, watched in amazement as a tiny atomic clock that was the size of a four-slice pizza was launched into space from a satellite attached by one of the strongest rockets in the universe at 2:30 AM. Ely clearly recalls the bright flashing sound and the beating vibration that continued long after the light dimmed. He recalls feeling it in his chest.
Eric Burt, an expert on atomic clocks and physicist with Elys, was also present at the site. Burt was shocked by the violence of the launch, despite all the shake tests that had been performed to ensure the delicate device would withstand the trip into space. He recalls that the whole Earth shakes. It was three miles away and I thought: How can our little clock ever survive?
It did. Ely and Burt, two of NASAs Jet Propulsion Laboratory's leaders in the Deep Space Atomic Clock Project, were able to power off the clocks satellite in September, more than two years after their deployment into low-Earth orbit. This marked the end of its initial mission. It is the most accurate clock ever used in space and it has opened the door to real-time navigation throughout the cosmos. Ely, principal investigator of the project, said that a robust onboard navigation system will be an essential component for human exploration beyond Earth. Our clock can also play a part in this.
Like all other types of clocks, atomic clocks start with an oscillator. This is a device that vibrates. Burt says that it could be as simple a swinging pendulum or a quartz crystal, like the one in your iPhone or watch. This frequency or the number of oscillations that occur per second is what clocks use to keep time.
Oscillators can be fickle. The stability of their frequency decreases over time, a phenomenon called drift. Burt says that atomic clocks combine an oscillator and a collection of particles to keep the frequency stable. This clock uses mercury, while others use cesium, rubidium or strontium. Atoms are composed of electrons that circle a nucleus. These electrons can only exist in certain orbits depending on how much energy they have. The electrons must have the right energy to jump into higher orbits. Scientists can observe the activity of the atoms it pairs with to monitor their clocks' stability. Burt says that one way to see it is that the atomic part is a steering wheel for the oscillator. You will see lots of atoms moving around if it is at the correct frequency. It doesn't matter if it is at the wrong frequency.
The team published a Nature paper in June reporting that their clock had extremely low drift. This corresponds to a deviation less than four billionthsof a second over 23 days. Burt says that this clock would lose one second over 1,000 years at this rate. This clock is more accurate than any other currently operating in space. Although ground-based clocks can still be ten to 100 times as accurate, it would still be slightly off after approximately 90 years. He says that we would have been content to show its operability. It would have been great if it had worked and then stopped working ten minutes later.