During the space race of the 1960s the United States and the Soviet Union competed for space firsts across a broad front of human and robotic missions targeted on the Moon, Venus, and Mars. The United States won the most significant prize by landing a human on the Moon first, demonstrating its capability so thoroughly that the Soviet Union seceded from the race and misleadingly claimed that it had not been racing the U.S. at all. Regardless, it succeeded in landing the first robotic rovers on the Moon. Lunokhods 1 and 2.
The first, Lunokhod 1, landed on November 17, 1970, when the Soviet Luna 17 spacecraft soft landed the vehicle on the lunar surface. Weighed just under one ton, this rover was intended to operate for 90 days while guided from the soviet mission control outside Moscow. It had been launch on November 10, 1970, and flight controllers undertook two course corrections (on November 12 and 14) to bring it into lunar orbit on November 15. After landing, this eight-wheeled rover departed Luna 17 by means of ramps extending from ramps on both sides of the lander.
Lunokhod 1 far exceeded its design life, and traveled around the lunar Mare Imbrium (Sea of Rains) for 11 months after landing. It ran only during the two-week long lunar day, stopping occasionally to recharge its batteries via its solar panels.The rover’s operations officially ceased on October 4, 1971, on the 14th anniversary of the launch of Sputnik 1. It was the first roving remote-controlled robot to land on another world.
Viewed initially as a scout for a landing site for Soviet cosmonauts, this rover originated in 1963 and was to carry a beacon that would be used to guide the cosmonauts to the surface. By the time that it flew, however, this mission had been overcome by events. Lunokhod 1, therefore, explored the lunar surface and returned scientific information about the geology and landscape of the Moon, image its surface, undertake laser ranging experiments from Earth, and measure magnetic fields. It carried a cone-shaped antenna, a highly directional helical antenna, four television cameras, and an extendable arm to test the lunar soil for soil density. Soviet scientists also included an x-ray spectrometer, an x-ray telescope, cosmic-ray detectors, and a laser ranging device.
Lunokhod 1 had a unique design; it looked like a bathtub on eight wheels. The inside of the large convex lid served as the solar array tub and the tub itself housed the instruments. Using imagery from a large panorama camera, a five-person team of controllers on Earth sent commands to the rover in real time to control its movement.
Greatly exceeding its anticipated life, Lunokhod 1 had traveled a total of 10,540 meters and transmitted more than 20,000 TV pictures and more than 200 TV panoramas back to Earth. It also conducted more than 500 lunar soil tests. The exact location of Lunokhod 1 on the lunar surface is uncertain because laser ranging experiments have been unable to detect a return signal since the end of the mission.
Lunokhod 2 was a virtual twin of its predecessor. Launched on the Luna 21 spacecraft on January 8, 1973, after a midcourse correction the day after launch, Luna 21 entered orbit around the Moon on January 12. Its orbital parameters were 100 x 90 kilometers at 60° inclination. The spacecraft then soft-landed on the Moon between Mare Serenitatis and the Taurus Mountains and deployed the second Soviet lunar rover (Lunokhod 2) on January 15 less than three hours after landing.
The 840-kilogram Lunokhod 2 was an improved version of its predecessor and was equipped with a third TV camera, an improved eight-wheel traction system, and additional scientific instrumentation. Like its predecessor, this rover’s primary objectives included imagery of the lunar surface, laser ranging experiments, solar X-rays analysis, magnetic field measurements, and testing of the properties of lunar surface material.
By the end of its first lunar day, Lunokhod 2 had already traveled further than Lunokhod 1 in its entire operational life. Lunokhod 2 operated for 4 months, covered 37 km (23 miles) of terrain, including hilly upland areas and rilles, and sent back 86 panoramic images and over 80,000 TV pictures. It also completed several tests of the surface, laser ranging measurements, and other experiments. On May 9, 1973, the rover rolled into a crater and dust covered its solar panels, disrupting power to the vehicle. Mission controllers attempted to salvage the rover but failed to do so.
On June 3, TASS, the Soviet news agency announced that the Lunokhod 2 mission had been terminated. The rover remains a target for laser ranging experiments to the present.
Interestingly, after the end of the Lunokhod 2 mission, Soviet scientists confided that an American scientist working on the Apollo program had given images of the lunar surface near the Luna 21 landing site to Soviet colleagues at a conference on planetary exploration in Moscow, on January 29-February 2, 1973. Those images had been taken as part of the planning for the December 1972 Apollo 17 lunar landing mission that took place in the same region. This was after the landing of the spacecraft, but they proved helpful to the controllers in navigating the rover on the Moon.
In addition, the Soviet Union succeeded with two sample return missions from the Moon. After several failed attempts the first, Luna 20, was placed in an intermediate Earth parking orbit and from this orbit was sent towards the Moon. It entered lunar orbit on February 18, 1972. On February 21, 1972, Luna 20 soft landed on the Moon in a mountainous area known as the Apollonius highlands near Mare Foecunditatis (Sea of Fertility), 120 km. While on the lunar surface, the panoramic television system returned imagery. It also collected lunar samples by means of an extendable drilling apparatus. The ascent stage of Luna 20 was launched from the lunar surface on February 22, 1972, carrying 30 grams of collected lunar samples in a sealed capsule. It landed in the Soviet Union on February 25, 1972. The lunar samples were recovered the following day.
A second successful sample return mission, Luna 24, landed in the area known as Mare Crisium (Sea of Crisis) August 18, 1976. Like its predecessor, it used a sample arm and drill to collect 170.1 grams of lunar samples and deposited them into a collection capsule. The capsule then returned to Earth on August 22, 1976, in western Siberia.
These robotic missions are not well known by many people except the true space enthusiast but they represented a very successful effort to explore the Moon from afar with surrogates.