Moonlight: Towards a Time-Zone Space Shuttle for Astronauts and Robotic Explorators in the United States and Europe
It will take new technologies on Earth to be deployed 239,000 miles away. Javier Ventura-Traveset, an engineer at the European Space Agency, is leading this work with a project called Moonlight, which aims to design satellites for astronauts and robotic explorers. Moonlight and its US counterpart, the Lunar Communications Relay and Navigation Systems, will support NASA’s Artemis program, and the work is raising questions about whether the moon should have a single time zone—and how that would work.
“We’re just starting to lay this out,” says Cheryl Gramling, an aerospace engineer who leads the position, navigation and timing team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The lunar clock and its implications for lunar communication networks, satellite navigation systems, and Internet and gps: What will we learn from the lunar activity?
Defining lunar time is not simple. The definition of the second is the same everywhere but the special theory of relativity dictates that clocks tick slower in stronger fields. The lunar clock would run faster than the Earth’s one if an observer on Earth were to observe it. Gramling predicts that a lunar clock would gain 56 microseconds over 24 hours. The clock speed on the moon would not be the same as on Earth, due to the moon’s rotation. She believes that it’s a good place for experts in Einstein’s theory of relativity.
The most pressing need for lunar time comes from plans to create a dedicated global satellite navigation system (GNSS) for the Moon, similar to how GPS and other satellite navigation networks enable precise location tracking on Earth. Space agencies plan to install this lunar GNSS from around 2030. The European Space Agency approved a lunar satellite navigation project called ‘Moonlight’ at a meeting of its ministerial council in Paris in November 2022, and NASA established a similar project called ‘Lunar Communications Relay and navigation Systems’ in January.
In 25 years, astronauts will return to the moon and eventually build bases and space stations, as well as mining for resources. In this bustling new era of lunar activity, they’ll need to synchronize with each other. There isn’t an agreed-upon time system or zones yet, and neither internet nor gps is available on the moon.
In this scenario, days on the Moon could even be defined differently from those on Earth, to account for the time from solar noon to solar noon taking an average of 29.5 Earth days. Earth days will always matter to astronauts, given the human need for sleep on a roughly 24-hour cycle. Metrologists need to agree on the definition.
Setting Lunar Time: Is It Necessary for Space Agency Standards to be Interoperable? Astronauts Can’t Just Use a Single Time Zone
The Interagency Operations Advisory Group is a council of national space agencies that talks about space agency standards for things like maps of the lunar terrain and coordinate systems for navigation. To make various countries’ systems interoperable, reference systems will have to be agreed internationally, says Gramling.
NASA is developing a framework called LunaNet which it hopes will get international buy-in. LunaNet consists of a set of rules that would enable all lunar satellite navigation, communication and computing systems to form a single network similar to the Internet, regardless of which nation installs them. Setting lunar time is part of a much bigger picture.
Everyone agrees on the definition of a second. If you’re curious, it’s 9,192 million cycles of microwave radiation emitted by a cesium atom. But that’s not really helpful when it comes to navigating everyday life. People need larger chunks of time to do things like set a clock or run a computer or know when to go to work or how long it takes to get from point A to point B. On Earth, we use a 24-hour day, based on the planet’s rotation and cycles of light and dark, to which our circadian rhythms are tuned.
But our lunar neighbor rotates much more slowly—every 29.5 Earth days. The side of the moon lit by the sun is pointed away from it for a long time. The moon is locked in with us, so we don’t notice the lunar rotation. It takes as long to revolve along its axis as it does to rotate around the planet, so the same side of the moon always faces us.) People like Ventura-Traveset need to define what time means in a place where many of the cues we use on Earth—sunrise, sunset, rush hour, prime time—are no longer there to guide us.
Ventura- Traveset says whether space agencies use a single time zone or several hasn’t been decided. It makes sense to have fewer zones because the moon is so slow. To him, the most natural way to accommodate astronauts would be to have a Coordinated Universal Time zone where they could follow a cycle consistent with the International Space Station. Sure, each day will be out of sync with the moon’s light and dark periods, but he doesn’t think it makes sense to have a weeks-long “day” followed by a weeks-long “night.”