What time is it right now? If you’re in the UK then that might be a bit of an issue because this weekend sees Daylight Savings Time begin.
In the longer term there’s also the issue of whether we need to use a negative-second to account for the fact that the Earth is suddenly spinning faster.
But what do you do it you’re on the Moon? Not much because it’s a timeless anarchy up there. Not for long.
Cue LunaNet, a proposed new system to provide timing and positioning information for anyone or anything on and around the Moon.
“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,” said Javier Ventura-Traveset, the European Space Agency (ESA)’s Moonlight Navigation Manager, coordinating ESA contributions to LunaNet.
There are multiple Global Navigation Satellite Systems (GNSS) around Earth. The GPS (Global Positioning System) is owned by the U.S. Government while Galileo is Europe’s version. China uses BeiDou, Russia GLONASS, India IRNSS and Japan QZSS.
They work by using fleets of satellites whose onboard clocks are synchronised while their orbital positions are monitored by receivers on the Earth’s surface. Those receivers record each satellite’s precise timestamp and calculate the length of time it takes for each signal to reach it. Using that data it’s possible to calculate the receiver’s 3D position—in longitude, latitude and altitude—relative to the satellites.
“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, ESA’s chief Galileo engineer, though as well as meter-level accuracy on Earth the system is also heavily used by satellites.
Haln points out that timekeeping on the Moon will have unique challenges. “Time passes at a different rate there due to the Moon’s specific gravity and velocity effects,” he said.
Why we need ‘Moon Time’
Why we need to be able to tell the time on the Moon is because our natural satellite is about to be visited by a lot of spacecraft. Not only NASA’s Artemis moon missions—the first of which looped around and beyond the Moon late in 2022—and its orbiting Lunar Gateway station, but myriad private missions to both the lunar surface and to cislunar space, the Moon’s sphere of influence.
Many of these missions will be close to the Moon at the same time and many will need to work with each other. An international agreement on a common lunar reference time is therefore crucial if they are to communicate as well as navigate and fix their own positions.
Part of the ESA’s drive to pin-down lunar time is its advanced plans for Argonaut, a lunar lander for all kinds of cargo delivery—whether robotic or to support crewed landings—that would give the space agency independent access to the surface of the Moon.
What the quest for timekeeping for the Moon doesn’t take into account is that on the surface of the Moon—where one side is tidally-locked to Earth—a day lasts 29.53 Earth-days. Half of that is a freezing cold night lasting about a fortnight.
Despite that, the Moon is only first of the list for ESA, according to Bernhard Hufenbach, a member of the Moonlight Management Team from ESA’s Directorate of Human and Robotic Exploration: “Having established a working time system for the Moon, we can go on to do the same for other planetary destinations,” he said.
Wishing you clear skies and wide eyes.
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