Published: 02/10/2020

ESA Discovery studies lay path to navigating the Moon

GPS satellites – like those of Galileo, Russia’s Glonass or their Japanese, Chinese and Indian counterparts – aim their antennas directly at Earth. Any satellite orbiting above the GPS constellation can only hope to detect signals from over Earth’s far side, but the majority are blocked by the planet. For a position fix, a satnav receiver requires a minimum of four satellites to be visible, but this is most of the time not possible if based solely on front-facing signals. Instead, GIOVE-A has been able to make use of signals emitted sideways from GPS antennas, within what is known as ‘side lobes’. Just like a flashlight, radio antennas shine energy to the side as well as directly forward. – © ESA

Just as we navigate our way around Earth’s surface using the connection between our phones and navigation satellites high above us, our missions use the very same satellites to navigate their way in space.

Around ten years ago, engineers started demonstrating that spacecraft outside the orbit of navigation satellites could also navigate in space using ‘spill over’ signal from the satellites.

ESA has invested in the development of an appropriate receiver, and is exploring whether it could be demonstrated on the Lunar Pathfinder mission. It will help lay the groundwork for providing navigation services around the Moon, currently studied through two ESA NAVISP activities and culminating in the Moonlight initiative.
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