Driving on Another World: How the Apollo 15 Lunar Rover Explored the Moon with Silver-Zinc Batteries and Wire-Mesh Tires

The T-Handle Controller and One-Sixth Gravity Handling

Driving a vehicle on the Moon presented unique vehicle dynamics challenges. With only one-sixth of Earth's gravity and no atmosphere, vehicle traction was low and the rover bounced easily over undulating crater rims. Instead of a traditional steering wheel and foot pedals (which were impossible to operate in stiff, pressurized spacesuit boots), the LRV used a single T-shaped joystick mounted between the two seats.

Pushing the T-handle forward applied proportional voltage to all four electric wheel motors; pulling back engaged mechanical drum brakes on all four wheels; tilting left or right activated double-Ackerman steering motors on both front and rear axles, allowing the rover to pivot with a tight 10-foot turning radius.

Dead-Reckoning Navigation in a Cratered Wasteland

Because the Moon possesses no global magnetic field, standard magnetic compasses are completely useless. To prevent astronauts from becoming lost in the disorienting lunar landscape where distances are difficult to judge by eye, GM Delco engineered an analog/digital dead-reckoning navigation system.

The system integrated a directional gyroscope with digital wheel odometer pulse counters. An onboard computer continuously calculated the vehicle's vector distance and heading, continuously displaying the precise range and bearing angle back to the Lunar Module Falcon at all times.

The Grand Canyon of the Moon: Standing at Hadley Rille

During their first traverse on July 31, Scott and Irwin drove south toward the rim of Hadley Rille—a massive sinuous lava tube collapsed into an 80-mile-long, 1,000-foot-deep volcanic canyon. The rover's color television camera, remotely controlled from Houston by flight controller Ed Fendell, beamed live panoramic images of layered basalt lava flows in the canyon walls back to millions of television viewers on Earth.

Across three EVAs, the Apollo 15 rover traveled a cumulative distance of 27.9 kilometers (17.3 miles). At the conclusion of the mission, Scott parked the rover a half-mile away from the lander, turning its camera to broadcast the first live color television footage of an Apollo ascent stage lifting off from the Moon to return home.

What the evidence does not settle

During the initial power-up on July 31, the front-wheel steering motor failed to respond due to an electrical connection glitch, though the astronauts successfully operated the vehicle using rear-wheel steering alone until the front steering automatically resumed functioning during the second moonwalk.