Even rightly so, too often the Apollo program dominates the narrative of early lunar exploration. The Soviet Union ran its own lunar program in the 1960s and '70s, and it was so successful early on that it looked like the Moon would be Soviet territory.
The first ever man-made object to land on its surface in 1959 was the Soviet-launched Luna 2. The first image of the lunar far side came during a flyby by Luna 3 the same year. In 1966, Luna 9 transmitted the first pictures from the surface of the Moon, and Luna 10 would enter into its orbit. In 1968, a handful of turtles and other simple organisms even made the first circumlunar voyage aboard Zond 5.
But Apollo 8 swept the rug out from the Soviet's feet; three astronauts going into orbit in December of that year all but assured the world that the political victory of landing on the Moon would go to the Americans. So the Soviets reshaped their lunar program, choosing to focus on inexpensive robotic mission that put science goals at the core.
Luna Sets The Stage
The Soviet's robotic visits to the Moon started with the Luna program. The first phase began in the late 1950s, with the first three missions designed as tests to scratch the surface of lunar exploration.
The second phase saw another 11 missions launched, each made to prove the program's technology was sound and worth pursuing.
The third wave of Luna missions, 10 in total, made up the Soviet's detailed exploration of the Moon. Within this third phase were two more sophisticated means of lunar exploration — landers and rovers. These larger payloads used the four-stage Proton rocket and went into orbit before making precise landings on the surface.
Soviet Russia's robotic program and America's Apollo went head-to-head in July 1969. Luna 15 entered into lunar orbit on July 17, just two days before the Apollo 11 astronauts reached the Moon. The mission called for Luna 15 to return a soil sample the day after Apollo 11 splashed down, not overshadowing the U.S. achievement but matching it scientifically. But on July 21, as the Eagle launched from the Sea of Tranquility, Luna 15 crashed into a mountain during its descent to the Sea of Crises.
Two months later on September 20, Luna 16 landed safely on the Sea of Fertility and managed a successful sample-return mission. Impressive as that was, the Soviet Union's robotic missions were about to evolve once more as its space program readied the Lunokhod rovers.
The Lunokhod Rovers
The Lunokhod rovers were designed to withstand the challenges of extended exploration in the lunar environment. It was built to survive the blistering 240°F heat of the two-week long lunar day, then survive the frigid, -290° two-week-long lunar night. Designers dealt with temperature changes by keeping the rover's key components in a pressurized shell and adding a cover. When open, solar arrays on the inside charged the rover's batteries. It could be closed for hibernation during the lunar nights. To regulate the rover's internal temperature, radioactive polonium-210 kept the vital components inside warm.
For locomotion, Lunokhod used eight individually controlled wheels supported by spokes and covered with wire mesh for improved mobility in powdery soil, but they were fixed. To turn, the driver would use more power on one side than the other, the same way a tank driver turns his vehicle.
Lunokhod would also have to be a surrogate for the scientists on Earth, so driving the rover was another challenge. Two five-man crews, chosen and screened from the Russian military's missile defense corps, shared the job. One member of each crew would drive the rover, backwards or forwards, using a joystick. It could go at one of two speeds: 0.5 or 1.2 miles per hour. The commander on a crew would sit behind the driver, monitoring his activity. A navigator, a radio antenna operator and a flight engineer, charged with monitoring the rover's systems, rounded out the crew.
Guidance came from a monitor that displayed images from Lunokhod's two low-resolution television cameras. The crew got single frames, like images in a slide show, every seven to 20 seconds. From those, they would control the rover in near real time. But because of the three second communications delay, the driver had to wait a number of seconds to see how well his commands had been executed. As a safety measure, the rover had a stop button the crew could press if they saw the rover heading towards trouble. It would immediately shut Lunokhod down.
The low resolution images made navigating around craters and boulders difficult. Particularly at lunar noon, when the sun was at too high an angle to cast helpful shadows; the crew shut operations down for three Earth days that corresponded with lunar noon. But the bigger navigation challenge was the "dead zone" in the rover's field of view — a three-foot-wide area immediately in front of it that the cameras couldn't see. The driver had to memorize the previous slide and any hazards before looking at the next image.
Lunokhod on the Surface
The first piece of Lunokhod hardware was actually launched independent of a rover on April 7, 1968. The Luna 14 mission carried a test electric motor into lunar orbit. The mission reached the Moon three days after launch and worked for another five before falling silent. Another shot on February 19, 1969, carried a Lunokhod but never made it to the Moon; the launch vehicle exploded, ending the mission.
Success came in 1970 with Luna 17. Launched on November 10, the craft orbited the Moon before landing in the Sea of Rains seven days later. After acquiring radio contact, the crew rolled the Lunokhod down a pair of ramps to make the first Soviet rover tracks on the Moon.
For 11 months the rover cycled between periods of activity during the lunar days, a forced stop during lunar noon, and hibernation during the lunar nights. In the last phase, the rover's cover would close and astronomers in Crimea and the French Alps would bounce a laser beam off a French-built reflector mounted on the rover. It was an experiment designed to provide accurate measurements of the Moon's periodic wobbles, and the distance between the Earth and our natural satellite.
As the mission wore on, controllers gained experience and confidence in their rover's abilities. Then, on October 4, 1971, Lunokhod 1 stopped responding to radio signals. It was fittingly on the anniversary of Sputnik's 1957 launch that the Soviet Union declared its first rover dead. Over the course of its mission, it traveled 6.5 miles, transmitted over 20,000 TV pictures and more than 200 TV panoramas, and conducted over 500 lunar soil tests.
The next Lunokhod arrived a month after Apollo 17 left the lunar surface. On January 15, 1973, Luna 21 landed on the eastern edge of the Sea of Serenity; the next day Lunokhod 2 rolled down onto the surface. It manoeuvered around to face and photograph its lander before setting off.
Building off the lessons learned and confidence gained from Lunokhod 1's mission, the crew didn't hold back with Lunokhod 2. But on May 9 they made one fatal misstep: the sun was behind the rover, giving the appearance of a smooth surface ahead, when really the rover was heading towards a crater. It drove straight in, but survived. What the crew should have done was close the lid and taken a panorama to see their surroundings and plot their route out. They didn't. Instead, they just pressed on, trying to manoeuver out. In doing so, they brushing the side of the crater with the lid. They knew it immediately; the power dropped out suddenly as regolith covered the solar panels. As Lunokhod 2 entered the next lunar night, the crew had no choice but to close the lid, dumping the Moon dust on the rover's radiator that released built-up heat during the lunar days. With material covering this vital instrument, the rover emerged from hibernation and started overheating immediately.
The mission ended on June 3; the Soviets declared the rover dead. Lunokhod 2 hadn't lasted as long as its predecessor, but it packed just a shade under 23 miles into its mission, over 80,000 TV pictures and 86 TV panoramas, and over 700 lunar soil tests. All in all, it a striking success.
The Future that Wasn't
Building off the successes of Lunokhods 1 and 2, the Soviet Union planned on sending a third rover to the Moon. They also considered a more ambitious mission called Sparka, which would send a team of Lunokhod-type rovers to the surface with a sample return vehicle; the rovers would drive to interesting sites, collect samples, and deposit them in the sample return vehicle that would take the collection Earth. It would be scientifically on par with the material returned by Apollo astronauts, but it never came to fruition. The Soviets turned their attention to Mars midway through the decade, ending an impressive and fruitful remote-controlled exploration of the Moon.