Foamy water and red-blue-green colored-stoplight as seen from a car’s windshield glass.
“The passage of time“ by Monica Hernandez. 2022

Keeping Time, The Crunch for Atomic Clocks in Space

The more we study the world at the quantum scale, including the behavior of atoms as markers of time and as exquisite sensors to probe unstudied matter, the more we might understand how to navigate to other worlds without having to depend on Earth-based antennas.

Monica Hernandez

The business of space has often required a standard notion of time that seems infinitely longer and more drawn out than most of our engineering endeavors. The bigger the mission, the longer it often takes. Some of the most complex missions have been planned with a timeframe that usually spans years and sometimes decades. The public has come to accept this as a mode of operation. Even the new space community or space 2.0 community (favoring the increased privatization of space science and engineering) accepts that space is about the long game, requiring time and effort that transcends many years and usually involves collaboration from many sectors.

From a business perspective, the long-term view needed in the industry might account for the continued hesitancy or reservations among many private investors and public institutions to believe in the industry’s profitability at its current stage. But how does the definition of time change when we measure time in space? And why is it becoming increasingly important to get the time right in space? It’s both a profound philosophical and technical question for us on Earth as it is for the prospects of navigating in deep space.

Albert Einstein’s theory of general relativity proposed time dilation — the difference in time elapsed measured by two clocks from differences in the gravitational field. In short, clocks can be used to calculate height and gravity based on the amount of time dilation. This study has been considered the holy grail in physics. And yet, the news is increasingly pointing to multiple efforts in the United States and worldwide to advance the refinement in performance of atomic clocks, quantum technological devices that operate at the tiniest scales.

Foamy water and red-blue-green colored-stoplight as seen from a car’s windshield glass.
”What is timekeeping?” by Monica Hernandez. 2022.

Atomic clocks leverage the fundamental properties of electrons which emit frequencies when they change energy levels. Roughly 400 atomic clocks in 70 laboratories worldwide maintain the International Atomic Time (TAI), setting the time standard and synching up all the clocks on Earth. In addition, atomic clocks are used on satellites in low Earth orbit, synching up with every GPS device and smartphone. However, spacecraft navigation in deep space continues to depend on atomic clocks on Earth, subject to delays, cosmic radiation, magnetic and gravitational interference, among many other factors that limit precision. These clocks measure how long a signal takes to make a two-way journey from the antennas on Earth to the spacecraft and the return signal from the spacecraft. A spacecraft’s navigation and orientation rely on distance and position, so timekeeping is a critical determinant in this calculation.

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