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How can we keep up with the time on the Moon?

With dozens of Moon missions planned for the coming decade, a new era of lunar exploration is on the rise. However, since all of these missions will soon be operating on and around the Moon, different teams will need to be able to communicate and fix their positions independently from Earth, thus requiring a commonly agreed upon way of keeping time on the Moon. This is part of a larger effort to agree a common ‘LunaNet’ architecture that will cover lunar communication and navigation services.

“LunaNet is a framework of mutually agreed-upon standards, protocols, and interface requirements allowing future lunar missions to work together, conceptually similar to what we did on Earth for joint use of GPS and Galileo,” explained Javier Ventura-Traveset, European Space Agency’s Moonlight Navigation Manager. “Now, in the lunar context, we have the opportunity to agree on our interoperability approach from the very beginning, before the systems are actually implemented.”

According to ESA navigation system manager Pietro Giordano, defining a common lunar reference time that is internationally accepted and towards which all lunar systems and users can refer to is of utmost importance and urgency to ensure the proper functioning and communication of future Moon missions.

“Interoperability of time and geodetic reference frames has been successfully achieved here on Earth for Global Navigation Satellite Systems; all of today’s smartphones are able to make use of existing GNSS to compute a user position down to meter or even decimeter level,” said Jörg Hahn, a chief engineer at ESA.

“The experience of this success can be re-used for the technical long-term lunar systems to come, even though stable timekeeping on the Moon will throw up its own unique challenges – such as taking into account the fact that time passes at a different rate there due to the Moon’s specific gravity and velocity effects.”

Although all the terrestrial satellite navigation systems, such as the United States’ GPS or Europe’s Galileo, operate on their own distinct time systems, they nevertheless posses fixed offsets relative to each other down to a few billionths of a second, as well as to the UTC Universal Coordinated Time global standard (the timing used for internet, banking, and aviation operations).

Scientists are now debating whether a single organization should be responsible for setting and maintaining lunar time, and whether this time should be kept synchronized with Earth time or be set on an independent basis on the Moon. Devising such a system is currently facing significant challenges, since clocks on the Moon run faster than their equivalents on Earth and their exact rate depends upon on their position on the Moon. 

Moreover, the agreed time system will also need to be practical for astronauts, which will require a common ‘selenocentric reference frame,’ similar to the International Terrestrial Reference Frame on Earth, which allows consistent measurements of precise distances between any locations on Earth.

“Throughout human history, exploration has actually been a key driver of improved timekeeping and geodetic reference models. It is certainly an exciting time to do that now for the Moon, working towards defining an internationally agreed timescale and a common selenocentric reference, which will not only ensure interoperability between the different lunar navigation systems, but which will also foster a large number of research opportunities and applications in cislunar space,” concluded Ventura-Traveset.


By Andrei Ionescu, Staff Writer

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