Lunar Roving Vehicle

Courtesy of NASA/JSC

The first astronauts on the Moon had to limit their explorations to objects within walking distance of the lunar module. Beginning with Apollo 15, the astronauts got a four-wheeled vehicle called the Lunar Roving Vehicle (LRV) that would give them a ride and took them farther away from the lunar module.

The Lunar Roving Vehicle (LRV) resembled a stripped-down dune buggy, but it could carry more than twice its weight in passengers, scientific instruments, and lunar soil samples. It was about 3 m long and 2 m wide, and had a 2.3 m wheelbase. With a wheel diameter of 81 cm, the fully loaded vehicle could carry 450 kg, and climb slopes as steep as 20ยบ. It had ground clearance of 35 cm on a flat surface and could negotiate steplike obstacles.

Powered by two silver zinc batteries driving electric motors on each of the four wire-mesh wheels, the vehicle had a top speed of approximately 13 km/h. During the astronauts' stay on the Moon, it could make several trips, totaling approximately 65 km.

The LRV traveled to the Moon in the cargo compartment of the lunar module. To save space, the vehicle's frame was hinged, with three segments that folded together. The four wheels folded against the chassis. When the astronauts left the lunar module for their extravehicular activities, one of them released the lunar roving vehicle from its storage compartment. Springs unfolded the vehicle and its wheels, and they locked into position. One astronaut could set up, activate, and check the vehicle by himself.

Two astronauts sat side by side in the open-frame vehicle. Between them was a joystick rather than a steering wheel. The vehicle could travel forward or in reverse at variable speeds. The driver set a toggle switch to provide power to the drive motors, then used the joystick to control movement. He tilted the stick forward to go ahead, backward for reverse, and left or right for steering, and pulled straight back to apply the brakes. All four wheels turned to steer around obstacles, and the turn radius was no more than the length of the vehicle.

Because of the time limits on the life-support systems in the astronauts' backpacks and potential fatigue of the astronauts, the lunar vehicle made three trips during their 3-day stay on the Moon. For safety reasons, the astronauts remained within 5 km of the landing site. From this distance they could walk back to the lunar module if the vehicle broke down.

The vehicle carried a lunar communications relay unit for communications with Earth when it was out of sight of the lunar module. It relayed voice and biomedical data from the astronauts, and sent television coverage back to Earth.

The Moon has a much smaller diameter than Earth, so the astronauts would quickly be over the horizon and out of sight of the lunar module. Since a magnetic compass would not work on the Moon, the LRV had a built-in navigation system that told the astronauts the direction and distance back to the lunar module, and the total distance they had traveled.

Each wheel was powered by a separate electric motor, which had a sealed drive to keep out lunar dust. Even if two wheel motors failed, the astronauts could drive the vehicle after decoupling the failed motor to free the wheel.