How and why US wants to establish a time standard for the Moon

Subject: Science and tech

Section: Space sector

Context:

Last week, the US White House officially directed the National Aeronautics and Space Administration (NASA) to create a time standard for the Moon.

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This time standard will help different international bodies and private companies to coordinate their activities on the lunar surface.

How does Earth’s time standard work?

Most of the clocks and time zones — a geographical region which uses the same standard time — of the world are based on Coordinated Universal Time (UTC), which is set by the International Bureau of Weights and Measures in Paris, France.
UTC is essentially an internationally agreed upon standard for world time.
It is tracked by a weighted average of more than 400 atomic clocks placed in different parts of the globe.
Atomic clocks measure time in terms of the resonant frequencies — the natural frequency of an object where it tends to vibrate at a higher amplitude — of atoms such as cesium-133.
In atomic time, a second is defined as the period in which a caesium atom vibrates 9,192,631,770 times.
As the vibration rates at which atoms absorb energy are highly stable and ultra-accurate, atomic clocks make for an excellent device for gauging the passage of time.
To obtain their local time, countries need to subtract or add a certain number of hours from UTC depending on how many time zones they are away from 0 degree longitude meridian, also known as the Greenwich meridian.
If a country lies on the west of the Greenwich meridian, it has to be subtracted from the UTC, and if a country is located on the east of the meridian.

Why do we need a time standard for the Moon?

A fundamental aspect of nature in the Universe is that time is not absolute.
But if you travel to the Moon, the clock would be ticking slightly faster than if you had stayed on the Earth.
This is a consequence of Albert Einstein’s Theory of General Relativity which tells us that gravity bends space and time.
The discrepancy may seem small but it can create problems for situations such as a spacecraft seeking to dock on the Moon, data transferring at a specific time, communication, and navigation.
Currently, handlers of each lunar mission use their own timescale that is linked to UTC.
This approach can work for a handful of independent lunar missions, but issues will arise once there are multiple spacecraft working together at the same time — a situation which is bound to become a reality in the near future.

How will a lunar time standard be established?

The specifics for creating a time standard for the Moon are not clear yet.
Like on the Earth, atomic clocks can be deployed on the lunar surface to set a time standard.
There will be a need to place at least three atomic clocks on the lunar surface that will tick at the Moon’s natural pace, and whose output will be combined by an algorithm to generate a more accurate virtual timepiece.
Mascons or mass concentrations are so dense that they alter the Moon’s local gravity field.
These effects are minor but the output from these clocks can be synthesized to give the Moon its own independent time, which can be tied back to UTC for seamless operations from Earth as well.
Even on Earth, atomic clocks have been placed at different locations or rather latitudes.
These clocks tick at different rates due to changes in Earth’s rotational speed varying from the Equator to the poles, which also affects time.
The planet rotates faster at the Equator than it does at the poles as it is wider at the Equator.