When the first people set foot on the Moon for long-term projects, they’ll need a lot of things, including their own time zone. That makes sense since they’ll be on an entirely different world. And, they’ll depend on a whole new set of technologies that will need time coordination with each other. So, space agencies are now figuring out what time zone the Moon will have.
Why worry about lunar time? Dozens of missions operating all at once will need to communicate with each other. Lunar satellites will need to fix their positions with respect to the Moon. The Gateway Lunar Station, for example, will be a transfer point between Earth and the lunar surface. Spacecraft will take lunar inhabitants back and forth between the two. All that coming and going requires that the missions operate on a common timescale. Both NASA and ESA are developing frameworks that will help coordinate interoperability and fix the timescale missions will use.
Last November, members of the European Space Agency met to discuss issues of timing, the lunar time zone, and the ongoing development of the NASA “LunaNet” architecture. “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,” said ESA engineer Pietro Giordano. “A joint international effort is now being launched towards achieving this.”
Coordinating All The Missions and Their Timekeeping
At the moment, missions to the Moon use the time zones of their home bases to coordinate activities and communications. Deep-space antennas keep onboard chronometers synchronized with Earth time. That will change in the (somewhat) near future because the Moon’s going to be a busy place. For example, once complete, the Gateway station will be open to astronaut stays. Regular Artemis launches will send crew and supplies. Eventually, there’ll be the long-awaited human return to the lunar surface. That will lead to the creation of a crewed base near the lunar south pole. A number of uncrewed missions will also take place. For example, each Artemis mission will release numerous lunar CubeSats. ESA will be putting down its Argonaut European Large Logistics Lander.
LunaNet concept graphic for a possible communication and navigation device used on the Moon. Credits: NASA/Reese Patillo
To help coordinate those activities, NASA created “LunaNet” to handle lunar communication and navigation services. ESA created its Moonlight program in a similar effort to maintain links between its satellites and Earth. Like LunaNet, Moonlight will need a shared common time reference to link missions and facilitate position fixes. Since dozens of missions will operate in lunar space and on the surface at any given moment, it’s important that they all work together in a lunar time zone.
ESA’s Moonlight initiative involves expanding satnav coverage and communication links to the Moon. The first stage involves demonstrating the use of current satnav signals around the Moon. This will be achieved with the Lunar Pathfinder satellite in 2024. The main challenge will be overcoming the limited geometry of satnav signals all coming from the same part of the sky, along with the low signal power. To overcome that limitation, the core of the Moonlight system will see dedicated lunar navigation satellites and lunar surface beacons providing additional ranging sources and extended coverage. Credit: ESA-K Oldenburg
Timing on the Moon Depends on Protocols Developed on Earth
“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, ESA’s Moonlight Navigation Manager, coordinating ESA contributions to LunaNet. “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.”
There is precedent for such interoperability already. On Earth, satellites share time signals based on commonly accepted measurements. Such programs as GPS and Galileo, as well as other systems, depend on those time signals. Jörg Hahn, ESA’s chief Galileo engineer and also advising on lunar time aspects pointed out that interoperability of time and geodetic reference frames is a settled technology here on Earth.
“All of today’s smartphones are able to make use of existing GNSS to compute a user position down to the meter or even decimeter level”, he said. “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.”
So, What Time Zone Will the Moon Have?
With all the discussion, nobody’s set the lunar time zone yet because there are some challenges. First of all, there’s a problem with the clocks. Moon clocks run faster than Earth clocks. They gain about 56 microseconds per day. And, that changes, depending on if they’re on the Moon or on the Gateway station.
Questions keep coming up, like should the Moon have a separate time zone or have one coordinated with somewhere on Earth? Should one organization set and maintain lunar time? If so, which one? These all need answers.
Of course, the agreed time system will also have to be practical for astronauts,” explained Bernhard Hufenbach, a member of the Moonlight Management Team from ESA’s Directorate of Human and Robotic Exploration. “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. But having established a working time system for the Moon, we can go on to do the same for other planetary destinations.”
Timing Depends on the Moon, Really
As part of all these timing deliberations, the international community will also have to settle on a common “selenocentric reference frame.” That’s similar to the International Terrestrial Reference Frame used here on Earth. It’s a framework for measuring points on the planet, centered on the center of Earth’s mass. The framework is updated every few years with new survey information. The idea would be to create the same reference framework for the Moon and use that for ongoing timekeeping and survey measurements.
“Throughout human history, exploration has actually been a key driver of improved timekeeping and geodetic reference models,” added Javier. “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.”
