Results of the Compensated Earth-Moon-Earth Retroreflector Laser Link (CEMERLL) Experiment

Adaptive optics techniques can be used to realize a robust low bit-error-rate link by mitigating the atmosphere-induced signal fades in optical communications links between ground-based transmitters and deep-space probes. Phase I of the Compensated Earth{Moon{Earth Retrore∞ector Laser Link (CEMERLL) experiment demonstrated the flrst propagation of an atmosphere-compensated laser beam to the lunar retrore∞ectors. A 1.06-„m Nd:YAG laser beam was propagated through the full aperture of the 1.5-m telescope at the Starflre Optical Range (SOR), Kirtland Air Force Base, New Mexico, to the Apollo 15 retrore∞ector array at Hadley Rille. Laser guide-star adaptive optics were used to compensate turbulence-induced aberrations across the transmitter’s 1.5-m aperture. A 3.5-m telescope, also located at the SOR, was used as a receiver for detecting the return signals. JPL-supplied Chebyshev polynomials of the retrore∞ector locations were used to develop tracking algorithms for the telescopes. At times we observed in excess of 100 photons returned from a single pulse when the outgoing beam from the 1.5-m telescope was corrected by the adaptive optics system. No returns were detected when the outgoing beam was uncompensated. The experiment was conducted from March through September 1994, during the flrst or last quarter of the Moon.