Not too long ago, astronauts roved the Moon

In 1964, NASA started thinking about sending astronauts to the Moon with some kind of vehicle that could help them wander farther on the lunar surface. The first proposals were wild and fanciful, and never came to fruition. It wasn't until 1969 that NASA began to develop a lunar rover in earnest for the final three Apollo missions. It was a tight time frame, but in less than two years, astronauts were driving on the Moon.

The First Rovers

It was NASA’s Marshall Space Flight Center that first studied how astronauts might travel on the Moon. It didn't take much imagination to realize that a vehicle would maximize the astronauts’ time spent exploring our satellite. The leading proposal was for a two-man, three-ton, closed-cabin mobile laboratory called MOLAB. Traveling up to 62 miles per hour (!), it would give a crew access to a huge area on the Moon while also providing them the safety of always having their habitat nearby. Some engineers took the idea of a roving habitat even farther, envisioning a future where fleets of these vehicles could walk, crawl, jump, and even fly around the Moon.

The idea of having a crew rove the Moon wasn’t realized until 1969. On April 7, a little more than three months before Apollo 11 launched, Wernher von Braun established a Lunar Roving Task Team. It was based at NASA’s Marshall Space Flight Center, the place where von Braun and his team had been developing rockets since the 1950s.

In this initial call for a rover, von Braun admitted that the vehicle would significantly complicate a mission. The additional hardware would make the lunar-bound payload heavier, increasing the cost and the risk. But it would be worthwhile. Driving would let the astronauts spend more time and energy collecting samples and deploying experiments than walking in their bulky pressure suits from site to site. And while von Braun knew that no vehicle could possibly be ready in time to launch with Apollo 11, he was sure the last few Apollo missions could benefit from some type of rover. Von Braun’s task team was approved by NASA headquarters two months later on May 23.

Apollo astronauts inspect a lunar rover.

Developing the Lunar Rover

Early in 1970, the lunar rover program reached its first milestone, when NASA awarded Boeing the contract to develop and build the lunar rover.

As the vehicle took shape, it was clear that the rover wouldn't be as complicated as a mobile laboratory but would serve some of the same functions. The rover would have to support the crew’s surface activities, meaning it would have to be built with human functionality in mind. But there were also practical considerations, including the Moon’s lack of atmosphere, a surface temperature that oscillates between plus and minus 250 degrees Fahrenheit depending on whether you're in light and shadow, a one-sixth gravity environment, the poorly understood lunar soil, and the barren and unfamiliar lunar landscape. The vehicle would have to be lightweight, powerful, and somehow keep the astronauts from getting hopelessly lost.

With these design factors in mind, the rover gradually took shape.

The Rover’s Systems

The lunar rover was powered by two 36-volt silver zinc batteries. These batteries drove quarter-HP electric motors at each wheel, eliminating the need for a transmission or gears. The wheels could pivot in place, giving the rover a 10-foot turn radius, exactly the length of the full vehicle. A T-shaped handle between the two seats let the astronauts drive the rover, functioning like a joystick.

The wheels were designed to minimize the crew’s chances of getting stuck in the dust or on a rock. The rover could climb over foot-high rocks up to 28 inches in diameter on woven mesh wheels made of zinc-coated piano wire, with titanium threads riveted in a chevron pattern overtop.

To keep a crew from getting lost (the barren and unfamiliar terrain promised to confuse even astronauts with excellent sense of direction) the rovers used a navigation system. A directional gyroscope acted as a stable reference point, calculating the vehicle’s heading. An attitude indicator to told astronauts whether they were driving on a hill or flat ground. A sun-shadow device determined the crews heading with respect to the Sun. And finally, odometers on each wheel generated information about speed and distance traveled.

Taken together, these navigation systems recorded the direction and distance a crew had traveled from their starting point (such as the Lunar Module). It was such an accurate system that no matter how far the crew traveled, they would be able to find their way back by retracing their steps. Navigation tracking also let NASA follow along on the astronauts’ drives, keeping tabs on their location and identifying interesting nearby sites they could visit. Sending this information back to Earth was the job of the rover’s communications systems. This consisted of a television camera, radio-communications equipment, and telemetry equipment.

Finally, a thermal protection system kept all of this stuff from succumbing to the Moon’s extreme temperatures by dissipating the excess heat they collectively generated.

The first lunar rover, Apollo 15, in 1971.

The Human Factor

The hardware was sound, and tests on Earth made sure the rover would work. But testing whether the crew could drive the rover was another matter. There were vehicles that simulated driving a rover in one-sixth gravity and mimicked the way astronauts would drive with a central joystick. But again, it was the practical matter that posed the biggest questions. Namely, would astronauts in bulky suits be physically able to drive a rover on the Moon?

To answer this question, engineers studied how astronauts related to the machine. Taking a lunar rover into NASA’s "vomit comet" and flying in parabolic arcs to simulate lunar gravity, technicians watched astronauts climb in and out of the rover. Seeing what worked and what didn't, they were able to determine the most efficient way for astronauts to physically fit in the rover, a study that resulted in nylon mesh seats with footholds and seat belts. Engineers also also studied how astronauts could manipulate the control switches while wearing gloves.

Apollo 16 astronauts inspect their lunar rover as it's folded into their Lunar Module's descent stage.

Roving the Moon

For all its impressive capabilities, the rover weighed just 460 pounds. And though it was about the size of a car, it could fold into a space of just four cubic feet. It traveled to the Moon in this stored state, fixed to the Lunar Module’s descent stage. One the crew landed on the Moon, the rover was outside waiting to be deployed.

Apollo 15 was the first mission to drive on the Moon. After landing at the Hadley-Apennine mountains, Dave Scott and Jim Irwin deployed their lunar rover on July 31, 1971. They lowered it slowly from its stowed position, stopping occasionally to double check with mission control (who was watching the live video feed) that everything looked good. The wheels, packed with springs, deployed automatically. Once on the surface, the crew only had to deploy the seats and the footrests and they were ready to drive.

The lunar rover did exactly what it was supposed to do. The farthest the Apollo 14 crew had traveled from their Lunar Module was just under a mile. The Apollo 15 crew more than tripled that distance, driving 3.1 miles from the safety of their LM. It was the last lunar mission, Apollo 17, which flew in December of 1972, that pushed the limits of the rover. They traveled the farthest (4.5 miles) from their LM and reached a top speed just over 11.5 miles per hour.

The lunar rovers that flew to the Moon with Apollo missions might not have been the sophisticated laboratories that forward-thinking engineers had dreamed about in the early 1960s, but they did exactly what they were designed to do. As NASA gained confidence, Apollo missions traveled farther with the rover, explored a wider variety of features on the Moon’s surface, and brought back a different types of samples. And because the Moon has no atmosphere and no weather, all those rover tracks are still on the surface today, visible by spacecraft from lunar orbit.

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