Laser Ranging to the Lost Lunokhod~1 Reflector

TL;DR

This paper reports the rediscovery and precise localization of the Lunokhod 1 lunar reflector, demonstrating its excellent condition and potential for scientific measurements due to its advantageous position and usability during lunar day.

Contribution

The paper provides the first precise selenographic position of Lunokhod 1 and assesses its condition, enabling its use in lunar laser ranging science.

Findings

Lunokhod 1 reflector is in excellent condition and stronger than Lunokhod 2 reflector.

The reflector is usable during lunar day, unlike Lunokhod 2.

Position determined with few-centimeter accuracy.

Abstract

In 1970, the Soviet Lunokhod 1 rover delivered a French-built laser reflector to the Moon. Although a few range measurements were made within three months of its landing, these measurements---and any that may have followed---are unpublished and unavailable. The Lunokhod 1 reflector was, therefore, effectively lost until March of 2010 when images from the Lunar Reconnaissance Orbiter (LRO) provided a positive identification of the rover and determined its coordinates with uncertainties of about 100 m. This allowed the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) to quickly acquire a laser signal. The reflector appears to be in excellent condition, delivering a signal roughly four times stronger than its twin reflector on the Lunokhod 2 rover. The Lunokhod 1 reflector is especially valuable for science because it is closer to the Moon's limb than any of the other reflectors and, unlike the Lunokhod 2 reflector, we find that it is usable during the lunar day. We report the selenographic position of the reflector to few-centimeter accuracy, comment on the health of the reflector, and illustrate the value of this reflector for achieving science goals.