The European Space Agency (ESA) has urged giving the Moon its own time zone, a reference that is internationally accepted and used without exception by all countries that send ships there. The measure, they explain, is motivated by the dozens of lunar missions planned for the next decade. Among the most important projects, the construction of the Gateway Moon Station o to nave Orionprepared to return humanity to the natural satellite of the Earth.
So far, each new mission to the Moon runs on the time of the country that operates the spacecraft. However, ESA considers that this way of working will not be sustainable in the future. Upon completion, the Gateway station will be open for astronaut stays, resupplied through regular NASA Artemis launches. This will allow humanity’s return to the lunar surface, culminating in a manned base near the south pole of the satellite. In the meantime, numerous unmanned missions will also take place (each Artemis mission alone will launch several Lunar CubeSats) and ESA will leave its lander Argonaut.
These missions will not only be on or around the Moon at the same time, but will also often interact, being able to transmit communications with each other or conduct joint observations or operations. Without a shared time slot, all of those interactions can struggle or end in chaos.
Consequently, space organizations have begun to consider how to keep time on the Moon. The discussion is part of a larger effort to agree on a common ‘LunaNet’ architecture covering lunar navigation and communication services.
“LunaNet is a mutually agreed framework of standards, protocols and interface requirements that allow future lunar missions to work together, conceptually similar to what we did on Earth for the joint use of GPS and Galileo,” explains Javier Ventura-Traveset, manager of ESA’s Moonlight Navigation, which develops a lunar navigation and communications service.
Moonlight will be joined in lunar orbit by an equivalent NASA-sponsored service: the Lunar Communications Relay and Navigation System. To maximize interoperability, these two systems should employ the same time scale, along with the many other manned and unmanned missions they will support.
gravity and speed
Jörg Hahn, ESA’s Chief Galileo Engineer who also advises on aspects of lunar time, recalls that stable timekeeping on the Moon will present its own unique challenges, such as accounting for the fact that time passes differently there due to to the specific gravity of the Moon and the effects of velocity. For example, clocks on the Moon run faster than their terrestrial counterparts, gaining about 56 microseconds, or millionths of a second, per day. In addition, they would also tick at different speeds on the lunar surface compared to their speed while in orbit.
All terrestrial satellite navigation systems, such as Europe’s Galileo or the United States’ GPS, operate with their own distinct timing systems, but these have fixed offsets of up to a few billionths of a second from each other, and also from each other. UTC (Coordinated Universal Time). It is the time used for Internet, banking and aviation standards, as well as for precise scientific experiments, maintained by the Paris-based Bureau International des Weights and Measures (BIPM).
The BIPM calculates UTC based on collections of atomic clocks maintained by institutions around the world, including ESA’s ESTEC technical center in Noordwijk, the Netherlands, and ESOC mission control center in Darmstadt, Germany.
practical for astronauts
Among the issues currently being debated is whether a single organization should be equally responsible for setting and maintaining lunar time. And also, whether lunar time should be set independently on the Moon or kept in sync with Earth.
“Of course, the agreed time frame will also have to be practical for astronauts,” explains Bernhard Hufenbach of ESA’s Directorate for Human and Robotic Exploration. “This will be quite a challenge on a planetary surface where in the equatorial region, each day lasts 29.5 days, including frigid fifteen-day lunar nights, with the whole of Earth a small blue circle in the dark sky. But having established a working time system for the Moon, we can do the same for other planetary destinations.”