Lunar Laser Ranging

Presenter: Tim Robert Trahan

Faculty Sponsor: Peter Olszak

School: Mount Wachusett Community College

Research Area: Physics and Nanotechnology

Session: Poster Session 4, 2:15 PM - 3:00 PM, Auditorium, A44

ABSTRACT

How do we measure the distance to the moon? During the Apollo program, retro reflectors were installed on the Moon by missions from the United States, the Soviet Union, and later India. Retro reflectors are specialized devices designed to reflect light directly back to its source. By sending a laser beam from Earth, reflecting it off one of these retro reflectors, and measuring the round-trip travel time; the distance can be calculated with great precision using the known speed of light.

Lunar laser ranging has been a valuable tool and has helped make many scientific breakthroughs. Some of the results of the experiments conducted with these reflectors are: the precise distance to the Moon with millimeter precision, the speed the Moon is moving away, the existence of a fluid core, tidal effects on the earth. These experiments are very difficult for many reasons, these include: atmospheric disturbances, beam divergence and return signal-to-noise ratio. While the laser propagates to the moon and back, it will go through many effects that need to be considered. For example, the return signal needs to be great enough to be detected. The strength of the return signal (photon flux) is significantly reduced by atmospheric disturbances and beam divergence.

This presentation will explore the logistics and history of these experiments, and discuss several of the technical challenges these experiments face and solutions to these problems as well as future experiments.

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