With dozens of lunar missions, including probes operating on and around the Moon planned for the coming decade, ESA says there is a need for the Earth’s natural satellite to have its own time zone as some of the future spacecrafts will likely be communicating and working together.
The space agency highlighted the “importance and urgency” for such a synchronicity by defining an internationally accepted common lunar reference time towards which all lunar systems and users may refer to.
This discussion, that began with a meeting at ESA’s ESTEC technology centre in the Netherlands last November, is part of a larger effort to agree on a common “LunaNet” architecture covering communication and navigation services on the Moon.
“During this meeting at ESTEC, we agreed on the importance and urgency of defining a common lunar reference time, which is internationally accepted and towards which all lunar systems and users may refer to,” ESA navigation system engineer Pietro Giordano said in a statement.
“A joint international effort is now being launched towards achieving this,” he added.
While new missions to the Moon until now have operated on their own individual timescales using deep space antennas to keep onboard chronometers synchronised with Earth time, experts say this way of time keeping will not be “sustainable” in the coming lunar environment.
As several missions are likely to be operating on or around the Moon at the same time and also interacting often with each other in the coming decade, a shared common timescale would be needed for crafts to efficiently carry out their operations, they said.
“Looking ahead to lunar exploration of the future, ESA is developing through its Moonlight programme a lunar communications and navigation service,” Wael-El Daly, system engineer for Moonlight, explained.
“This will allow missions to maintain links to and from Earth, and guide them on their way around the moon and on the surface, allowing them to focus on their core tasks. But also, Moonlight will need a shared common timescale in order to get missions linked up and to facilitate position fixes,” he added.
Moonlight is planned to be joined in lunar orbit by an equivalent service sponsored by NASA, the ESA noted, adding that the two systems by the space agencies should employ the same timescale in order to maximise interoperability between them.
For instance, on Earth, while the US GPS and Europe’s Galileo run on their own distinct timing systems, these systems possess fixed offsets relative to each other down to a few billionths of a second that help provide accurate navigation.
“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 metre or even decimetre level,” Jörg Hahn, ESA’s chief Galileo engineer explained.
“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,” he added.
Teams are discussing to determine if a single organisation should be responsible for setting and maintaining lunar time, and whether this should be set on an independent basis on the Moon or kept synchronised with Earth.
However, ESA says there are significant challenges as clocks on the Moon run faster than their terrestrial counterparts, gaining millionths of a second per day.
“This will be quite a challenge on a planetary surface where in the equatorial region each day is 29.5 days long, including freezing fortnight-long lunar nights, with the whole of Earth just a small blue circle in the dark sky,” Bernhard Hufenbach, a member of the Moonlight Management Team, said.
“But having established a working time system for the Moon, we can go on to do the same for other planetary destinations,” Dr Hufenbach said.
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