LunaNet: Standards for Telling Time on the Moon
A set of standards for telling time on the Moon dubbed LunaNet is being developed by multiple space organizations involved in the effort to return to the lunar surface.
“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.”
Javier Ventura-Traveset, ESA's Moonlight Navigation Manager
Dozens of Moon missions planned for the coming decade. As these missions will be operating on and around the Moon and needing to communicate together and fix their positions independently from Earth, this new era will require its own time. Accordingly, space organizations have started considering how to keep time on the Moon.
Beginning with a meeting at ESA’s ESTEC technology center in the Netherlands last November, the discussion is part of a larger effort to agree on a common ‘LunaNet’ architecture covering lunar communication and navigation services.
“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,” explains 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.”
Up until now, each new mission to the Moon is operated on its own timescale exported from Earth, with deep space antennas used to keep onboard chronometers synchronized with terrestrial time at the same time as they facilitate two-way communications. This way of working will not be sustainable however in the coming lunar environment.
Once complete, the Gateway station will be open to astronaut stays, resupplied through regular NASA Artemis launches, culminating in a human return to the lunar surface, progressing to a crewed base near the lunar south pole. Meanwhile numerous uncrewed missions will also be in place – each Artemis mission alone will release numerous lunar CubeSats – and ESA will be putting down its Argonaut European Large Logistics Lander.
These missions will not only be on or around the Moon at the same time, but they will often be interacting as well – potentially relaying communications for one another, performing joint observations or carrying out rendezvous operations.
LunaNet Discussion has Many Facets
Among the current topics under debate as LunaNet is developed is whether a single organization should be responsible for setting and maintaining lunar time as it is here on Earth, where the UTC Universal Coordinated Time global standard is maintained by the Paris-based Bureau International de Poids et Mesures (BIPM).
The BIPM computes UTC based on inputs from collections of atomic clocks maintained by institutions around the world, including ESA’s ESTEC technical center in Noordwijk, the Netherlands and the ESOC mission control center in Darmstadt, Germany. And also, whether lunar time should be set on an independent basis on the Moon or kept synchronized with Earth.
The international team working on LunaNet will face considerable technical issues. For example, clocks on the Moon run faster than their terrestrial equivalents – gaining around 56 microseconds or millionths of a second per day. Their exact rate depends on their position on the Moon, ticking differently on the lunar surface than from orbit.
“Of course, the agreed time system will also have to be practical for astronauts," explains 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.”
Finally, to work together properly, the international community will also have to settle on a common ‘selenocentric reference frame’, similar to the role played on Earth by the International Terrestrial Reference Frame, allowing the consistent measurement of precise distances between points across our planet. Suitably customized reference frames are essential ingredients of today’s GNSS systems.
(Source: ESA news release. Images provided)