The Lunar Laser Ranging Experiment (Bender et al., 1973)
- Original: P. L. Bender, D. G. Currie, R. H. Dicke, D. H. Eckhardt, J. E. Faller, W. M. Kaula, J. D. Mulholland, H. H. Plotkin, S. K. Poultney, E. C. Silverberg, D. T. Wilkinson, J. G. Williams, and C. O. Alley, “The Lunar Laser Ranging Experiment,” Science 182 (4109), 229–238, October 19, 1973. DOI 10.1126/science.182.4109.229.
- Rights: © AAAS — not a NASA public-domain document. The article itself is not redistributed in this library; it is cited by DOI (above), and the wiki draws only on its findings. See the copyright note below.
Summary
Section titled “Summary”The principal investigators’ four-year report on the experiment the Apollo 11 crew emplaced as the Laser Ranging Retroreflector (LR³). It recounts the experiment’s origin (Dicke’s Princeton group in the late 1950s, laser pulses bounced off the bare lunar surface by MIT in 1962), how the LR³ was rushed onto Apollo 11 as a contingency experiment when the full ALSEP proved too heavy for the first landing, the first successful returns, the ground-station technique, and the early science: a much-improved lunar orbit, libration parameters, and reflector/station coordinates.
Key takeaways
Section titled “Key takeaways”- A contingency experiment, quickly prepared. When word came (after September 6, 1968) that the astronaut workload on the first landing might be too heavy for the planned ALSEP, a proposal to fly the laser reflectors as a contingency experiment was “quickly prepared” — chosen for its scientific objectives, the reliability of a completely passive instrument, and the very short deployment time.
- First returns: Lick Observatory, August 1, 1969. Early attempts (the panel was placed on July 21, 1969) were hampered by the Moon low in the sky, landing-site uncertainty, instrument and weather problems; on August 1 the Lick 3.0-m telescope obtained strong returns (observed-minus-predicted range to 7 m), with high-confidence returns at McDonald 2.7-m soon after — then AFCRL (Arizona), Pic du Midi (France), and Tokyo.
- The hardware as flown: 100 solid fused-silica corner cubes, each 3.8 cm in diameter, recessed 1.9 cm in a 46-cm-square tippable panel; the illuminated spot on the Moon is ~4–6 km across, and the reflected return is 10–100× stronger than the natural surface reflection. Librations (up to ~11°) drove the recessed-corner thermal/optical design.
- Routine ranging at McDonald: a four-stage Korad Q-switched ruby laser (3 J, ~4 ns, one pulse per 3 s) through the 2.7-m at the coudé focus; timing electronics calibrated to 0.1 ns; successful runs per half-year grew 7 → 226 (1970–72); range residuals reached ~11 cm RMS (1 ns round trip ≈ 15 cm one-way).
- A growing reflector network: Lunakhod 1’s French-built panel (Nov 1970, no confirmed returns — possibly dust-coated), Apollo 14 (Feb 1971), the larger 300-cube Apollo 15 array (Jul 1971), and Lunakhod 2 (Jan 1973); the three Apollo reflectors form a triangle with 1250 / 1100 / 970 km sides, separating lunar rotation (libration) from orbital motion.
- Early science: the LURE-1 experimental lunar ephemeris from ~3 years of McDonald data; improved physical-libration theory; reflector coordinates good to ~50 m for Apollo 11; investigations of a long-standing lunar-longitude discrepancy (15 → 11 arcsec/century, source then unknown).
Copyright note
Section titled “Copyright note”This and the Dickey et al. 1994 companion are AAAS-copyrighted Science articles — unlike the NASA documents in this library they are not public domain. The articles themselves are therefore not redistributed here: each is cited by DOI (Bender, Dickey), and the wiki draws only on their facts and results — which are not copyrightable — linking to the published versions at Science.