The Lunar Laser Ranging experiment saw trays of retroreflectors left on the Moon by the astronauts of the Apollo 11, 14 and 15 missions, and later by two unmanned Soviet missions. Made up of many corner cube prisms, the retroreflectors enable precise laser ranging and exact measurement of the Moon’s distance from Earth. Those measurements have provided a foundation for scientific analysis of the Moon and its interior- including its liquid core – as well as tests of General Relativity.
Now NASA plans to expand the experiment by updating the technology used when it returns to the Moon in the coming years, initially with unmanned spacecraft. As well as building out the existing network, the new instrumentation will provide a 100-fold increase in ranging accuracy. The plan is to add three of these new instruments to the five already in situ on the lunar surface, giving a total of eight retroreflectors.
“Our Next Generation Lunar Retroreflector is a 21st Century version of the instruments currently on the Moon,” said lead scientist Doug Currie, professor emeritus at the University of Maryland and part of the team that designed the original instruments left by the Apollo missions.
“Each placement of a Next Generation lunar laser ranging array will greatly enhance the scientific and navigational capabilities of retroreflector network. These additions improve the mapping and navigation capabilities important for NASA’s plans to return to the Moon and by 2028 establish a sustained human presence.
“And these also will significantly boost scientists’ ability to use the network to conduct important science, such as new tests of general relativity and other theories of gravity. Such studies may help us understand the nature of mysterious dark matter, which appears to constitute almost 27 per cent of the Universe.”
The Next Generation Lunar Retroreflectors (NGLR) is one of 12 new science and technology payloads selected by NASA to help humans study the Moon and explore more of its surface as part of the Artemis lunar program. According to the space agency, these projects “will help the agency to send astronauts to the Moon by 2024 as a way to prepare to send humans to Mars for the first time.”