Forty-four years ago today, the Soviet lunar rover Lunokhod 1 landed in the Mare Imbrium, popularly known as the right eye of the Man in the Moon. It was the first planetary rover ever to successfully reach an extraterrestrial world, sparking a series of increasingly complex rover projects with ever more ambitious goals.
Read on for a visual history of the evolution of these robotic adventurers, from Lunokhod 1's inaugural voyage to the concept missions in development today.
The Soviet Lunokhod Programme
You might expect the first ever rover to be an aerospace relic, outpaced by the generations that followed it. But Lunokhod 1 is so sophisticated that it is still used for space research to this day.
In 2010, the exact location of the long-lost rover was pinned down by the Lunar Reconnaissance Orbiter. A few months later, astrophysicist Tom Murphy shot a laser at the rover, and discovered that its reflector had held up incredibly well.
"We got about 2,000 photons from Lunokhod 1 on our first try," said Murphy in a NASA statement about the rover's rediscovery. "After almost 40 years of silence, this rover still has a lot to say."
Lunokhod 1 is now enjoying an active second life as an integral part of Murphy's laser ranging studies, which are all about testing the limits of general relativity. But its first life was pretty damn eventful too. It soft-landed on the Moon on November 17, 1970, and proceeded to roll down the off-ramps of its mother ship Luna 17 like a boss.
From there, the rover spent the next eleven months wandering about six and a half miles across the ancient crater. Lunokhod 1 took over 20,000 pictures and conducted 500 analyses of soil samples during that time—an impressive haul for the world's first interplanetary rover.
Though Lunokhod's first run was capped off on October 4, 1971, when attempts to contact the unresponsive rover were finally abandoned, it was not the last of the Lunokhods. Lunokhod 2 landed in the Le Monnier crater on January 15, 1973, and traveled a whopping 24.2 miles over four months, the longest of any lunar rover to this day (though the Opportunity rover recently beat the record on Mars).
Though Lunokhod 3 never made it to the launchpad, the Soviet space program still really nailed their first foray into interplanetary roving. Obviously, NASA had to show them up with the first American lunar rover. And oh, how the agency delivered.
The Apollo Lunar Roving Vehicles
It's only natural that the milestone of walking on the Moon should be swiftly followed by the milestone of driving around it. That's just the American way. On August 7, 1971, the crew of Apollo 15 debuted these slick lunar roving vehicles, nicknamed "Moon buggies," in the Mare Imbrium—the same region that Lunokhod 1 was simultaneously exploring. For both the Americans and Soviets, interplanetary roving got its start in the same crater.
The Moon buggies defined the tail end of the Apollo program, and were included in the payloads of Apollo 15, 16, and 17. They allowed those final three crews to explore a much larger chunk of their landing sites, while also allowing easy transport of scientific equipment and lunar samples.
Above all, the roving vehicles were a futurist's dream. They are the only manned planetary rovers ever deployed, and provided an evocative snapshot of the future of civilization in space. Every frontier story requires a trusty vehicle, and Apollo's Moon buggies met the mark. Even so, lunar rovers were about to take a backseat to a new target: Mars.
The Prop-M Rover
Just as they were the first to land a rover on the Moon, so too were the Soviets the first to chuck one over to Mars. But their Martian Prop-M series of rovers were nowhere near as successful as the Lunokhod rovers had been. The first of the program's rovers, Mars 2, experienced a rough introduction to the planet on November 27, 1971, after the module's parachutes failed to open.
Though the loss of the payload was disappointing, the crash was still the first instance of any manmade object reaching Mars, regardless of its condition once it got there. The crash was further redeemed by the identical Mars 3 lander, which achieved the first Martian soft-landing five days later on December 2, 1971.
Unfortunately, the Mars 3 rover never got a chance to explore, due to a devastating transmission failure seconds after landing. It marked the last time the Soviet space program, or the Russian space program that succeeded it, ever attempted interplanetary roving.
The Sojourner Rover
It would be 26 years before another rover graced the surface of Mars, though plenty of stationary landers reached the Red Planet in the interim. Finally, in 1996, NASA launched the Mars Pathfinder mission, which included a modest rover called Sojourner. Appropriately enough, the rover landed on Mars on July 4, 1997, making the USA the first country to successfully deploy a rover on another planet.
The Sojourner was decked out with cameras and instruments, but it wasn't intended to be a particularly sophisticated rover. Weighing only 25 pounds, Sojourner traveled about 100 meters before communications with it broke down on September 27, 1997.
NASA's next two Martian rovers were much more ambitious projects, and ended up kicking the bar for interplanetary rover missions right into deep space.
The Mars Exploration Rovers
The Mars Exploration Rover Mission (MER) launched two rovers to our brother planet: MER-A, nicknamed Spirit, which landed on Mars on January 4, 2004, and MER-B, nicknamed Opportunity, which touched down on the opposite side of the planet three weeks later, on January 25.
These twin rovers are among the most successful of any spacecraft, having exceeded their planned mission durations by several years. Both were slated to take a brief stroll for 90 sols (92.5 days), but Spirit remained operational as a mobile science laboratory until May 1, 2009, and as a stationary lab until March 2010, when contact was officially lost with the rover.
Opportunity, meanwhile, is still roving around Mars's Meridiani Planum over a decade later. It has traveled about 25 miles, farther than any interplanetary rover, and continues to conduct experiments and send pictures back to Earth, most recently of a passing comet in Martian skies. The substantial bang that NASA got for its buck with the MER program explains why the agency upped the stakes even further with their next rover, Curiosity.
The Curiosity Rover
The Curiosity rover, home to the Mars Science Laboratory, is the the most expensive and sophisticated rover ever sent to Mars. It landed inside Gale Crater on August 6, 2012, after an almost laughably complicated landing sequence known as "the seven minutes of terror."
In the two years since its arrival, Curiosity has traveled about five miles and has made a series of major discoveries, most notably about the planet's capability of supporting microbial life during its prehistory. As of October, it has reached its target destination of Mount Sharp, and has since begun its ascent.
The Yutu Rover
China's Yutu rover was delivered to the Moon by the Chang'e 3 spacecraft on December 14, 2013, which was a historic accomplishment on a few levels. Not only was it China's first rover mission, it was the first soft-landing that any nation had achieved on the Moon since Lunokhod 2 touched down in 1973.
Despite its subsequent technical problems and maudlin death letter, the Yutu rover is a clear expression of China's aggressive investment in their space program. It's also a sign that in the future, NASA won't be the sole player in the interplanetary rover game.
For example, India is developing a lunar rover called Chandrayaan-2, which is slated for launch in 2017. The ESA is also hard at work on the ExoMars rover, which is expected to land on Mars in 2018. Given the recent slamdunks both of these agencies have enjoyed—with the Mission Orbiter Mars (MOM) and the Rosetta mission respectively—their first shot at rovers is very much anticipated.
The extraordinary technical advances rovers have made during the last 44 years points to a bright future of interplanetary exploration. Indeed, as I wrote in April this year, the next generation of rovers may take drastically different forms than the standard lab-on-wheels design that has prevailed so far.
Until humans can uproot and resettle on other planets, rovers will continue to be our eyes and ears on the distant worlds of our solar system, and perhaps beyond. And given that their future trajectory is shaping up to be at least as exciting as their storied history, it'll be quite an interesting ride.