The Lunar Roving Vehicle (LRV) was an electric vehicle designed to operate in the low-gravity vacuum of the Moon and to be capable of traversing the lunar surface, allowing the Apollo astronauts to extend the range of their surface extravehicular activities. Three LRVs were driven on the Moon, one on Apollo 15 by astronauts David Scott and Jim Irwin, one on Apollo 16 by John Young and Charles Duke, and one on Apollo 17 by Gene Cernan and Harrison Schmitt. Each rover was used on three traverses, one per day over the three day course of each mission. On Apollo 15 the LRV was driven a total of 27.8 km in 3 hours, 2 minutes of driving time. The longest single traverse was 12.5 km and the maximum range from the LM was 5.0 km. On Apollo 16 the vehicle traversed 26.7 km in 3 hours 26 minutes of driving. The longest traverse was 11.6 km and the LRV reached a distance of 4.5 km from the LM. On Apollo 17 the rover went 35.9 km in 4 hours 26 minutes total drive time. The longest traverse was 20.1 km and the greatest range from the LM was 7.6 km.
The Lunar Roving Vehicle had a mass of 210 kg and was designed to hold a payload of an additional 490 kg on the lunar surface. The frame was 3.1 meters long with a wheelbase of 2.3 meters. The maximum height was 1.14 meters. The frame was made of aluminum alloy 2219 tubing welded assemblies and consisted of a 3 part chassis which was hinged in the center so it could be folded up and hung in the Lunar Module quad 1 bay. It had two side-by-side foldable seats made of tubular aluminum with nylon webbing and aluminum floor panels. An armrest was mounted between the seats, and each seat had adjustable footrests and a velcro seatbelt. A large mesh dish antenna was mounted on a mast on the front center of the rover. The suspension consisted of a double horizontal wishbone with upper and lower torsion bars and a damper unit between the chassis and upper wishbone. Fully loaded the LRV had a ground clearance of 36 cm.
The wheels consisted of a spun aluminum hub and an 81.8 cm diameter, 23 cm wide tire made of zinc coated woven 0.083 cm diameter steel strands attached to the rim and discs of formed aluminum. Titanium chevrons covered 50% of the contact area to provide traction. Inside the tire was a 64.8 cm diameter bump stop frame to protect the hub. Dust guards were mounted above the wheels. Each wheel had its own electric drive, a DC series wound 0.25 hp motor capable of 10,000 rpm, attached to the wheel via an 80:1 harmonic drive, and a mechanical brake unit. Manuevering capability was provided through the use of front and rear steering motors. Each series wound DC steering motor was capable of 0.1 hp. Both sets of wheels would turn in opposite directions, giving a steering radius of 3.1 meters, or could be decoupled so only one set would be used for steering. Power was provided by two 36-volt silver-zinc potassium hydroxide non-rechargeable batteries with a capacity of 121 amp-hr. These were used to power the drive and steering motors and also a 36 volt utility outlet mounted on front of the LRV to power the communications relay unit or the TV camera. Passive thermal controls kept the batteries within an optimal temperature range.
A T-shaped hand controller situated between the two seats controlled the four drive motors, two steering motors and brakes. Moving the stick forward powered the LRV forward, left and right turned the vehicle left or right, pulling backwards activated the brakes. Activating a switch on the handle before pulling back would put the LRV into reverse. Pulling the handle all the way back activated a parking brake. The control and display modules were situated in front of the handle and gave information on the speed, heading, pitch, and power and temperature levels. Navigation was based on continuously recording direction and distance through use of a directional gyro and odometer and inputting this data to a computer which would keep track of the overall direction and distance back to the LM. There was also a Sun-shadow device which could give a manual heading based on the direction of the Sun, using the fact that the Sun moved very slowly in the sky. The image at left shows a diagram of the layout of the control and display module, the Sun-shadow device is at top center between the heading and speed readouts.
