ESA Lunar Pathfinder mission will use advanced satellite navigation

The ESA is talking about its Lunar Pathfinder mission to the moon. That mission will carry an advanced satellite navigation receiver and will perform the first satnav positioning fix in lunar orbit. The ESA says the experimental payload is a preliminary step in its plan to expand reliable satnav coverage and communication links to explorers around and on the moon during the decade.

Currently, the Lunar Pathfinder mission is expected to launch by the end of 2023, heading into lunar orbit. The mission is a public-private comsat that will offer commercial data relay services to lunar missions while stretching the operational limits of current satnav signals. The European Galileo constellation is a group of navigation satellites intended to deliver positioning, navigation, and timing services to the Earth.

Most navigational antennas on satellites in the constellation aim towards the Earth, blocking use from further away in space. However, ESA officials say that navigation signal patterns also radiate sideways like light from a flashlight. Past testing showed that the antenna "side lobes" could be employed for positioning if adequate receivers were used.

In the past, the ESA proved that higher-orbit positioning of navigation satellites was possible, and a growing number of satellites in geostationary orbit currently feature satnav receivers. Geostationary orbit is 35,786 kilometers above the Earth's surface, but the moon is ten times further away than that. The NASA Magnetospheric Multiscale Mission acquired GPS signals to perform a fix and determine its orbit from 187,166 kilometers away, about halfway to the moon.

That successful mission leads the ESA to believe the Lunar Pathfinder will be successful as its GPS equipment has significantly improved sensitivity. Its receiver will employ both Galileo and GPS signals with a high-gain satnav antenna. The expectation is that the receiver will achieve a positioning accuracy of around 100 meters, far more accurate than traditional ground tracking.