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World's Greatest Cars, Part 2

Lunar Rover: the only car literally out of this world

Courtesy NASA

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Driving on the Moon

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You are constantly dodging rocks and craters.

You hit a rock and you are literally airborne. You just bounce into space, float for a while, and then come down. Rover is a flying machine.

I've never liked safety belts, but we couldn't have done without them on the Rover. It had a definite pitching motion that was a cross between a bucking bronco and an old rowboat on a rough lake - up and down, up and down. You could easily get sea­sick if you had any problem with motion.

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At one point we came over a little rise and there was a crater about twenty feet deep right in front of us. Dave made a quick left turn that threw the vehicle up on the two right wheels. I felt sure we were going to flip. What if the thing did roll over and pin us underneath it? Could we ever release those seat belts and turn the Rover back over? We never had to find out.

We tore down the hill, getting back into the Grand Prix mood again. Just before we hit level, or almost level, ground Dave turned sharply. The front wheels locked and dug in, the rear end broke away, and around we went. We did a 180-degree reverse spin.

  • From ‘To Rule the Night’, by Apollo 15 Astronaut Jim Irwin

The Lunar Roving Vehicle 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.

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The Lunar Roving Vehicle had a mass of 210kg and was designed to hold a payload of an additional 490kg on the lunar surface. The frame was 3.1 metres long with a wheelbase of 2.3 metres. The maximum height was 1.14 metres.

The frame was made of aluminium alloy 2219 tubing welded assemblies and consisted of a 3-part chassis which was hinged in the centre 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 aluminium with nylon webbing and aluminium 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 centre 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 Lunar Roving Vehicle had a ground clearance of 36 cm.

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The wheels consisted of a spun aluminium 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 aluminium. Titanium chevrons covered 50% of the contact area to provide traction.

Inside the tyre 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.

Manoeuvring 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 metres, or could be decoupled so only one set would be used for steering.

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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 Lunar Roving Vehicle 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 Lunar Roving Vehicle 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 Lunar Roving Vehicle into reverse. Pulling the handle all the way back activated a parking brake.

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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 kept track of the overall direction and distance back to the Lunar Module. 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 only very slowly in the sky.

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The image here shows a diagram of the layout of the control and display module, the Sun-shadow device is at top centre between the heading and speed readouts.

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Deployment of the Lunar Roving Vehicle from the Lunar Module quad 1 by the astronauts was achieved with a system of pulleys and braked reels using ropes and cloth tapes. The rover was folded and stored in quad 1 with the underside of the chassis facing out. One astronaut would climb the ladder on the Lunar Module and release the rover, which would then be slowly tilted out by the second astronaut on the ground through the use of reels and tapes. As the rover was let down from the bay, most of the deployment was automatic.

The rear wheels folded out and locked in place and when they touched the ground, the front of the rover could be unfolded, the wheels deployed, and the entire frame let down to the surface by pulleys. The rover components locked into place upon opening. Cabling, pins, and tripods would then be removed and the seats and footrests raised.

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After switching on all the electronics, the vehicle was ready to back away from the Lunar Module. The here shows an earlier version of the planned deployment which does not exactly match the final sequence, note for example that the rover is facing away from the Lunar Module after deployment.

The original cost-plus-incentive-fee contract to Boeing (with Delco as a major sub-contractor) was for $19 million and called for delivery of the first Lunar Roving Vehicle by 1 April 1971, but cost overuns led to a final cost of $38 million.

Four lunar rovers were built, one each for Apollos 15, 16, and 17, and one that was used for spare parts after the cancellation of further Apollo missions.

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There were also other Lunar Roving Vehicle models built: a static model to assist with human factors design, an engineering model to design and integrate the subsystems, two 1/6 gravity models for testing the deployment mechanism, a 1-gravity trainer to give the astronauts instruction in the operation of the rover and allow them to practice driving it, a mass model to test the effect of the rover on the Lunar Module structure, balance and handling, a vibration test unit to study the Lunar Roving Vehicle's durability and handling of launch stresses, and a qualification test unit to study integration of all Lunar Roving Vehicle subsystems.

Three Lunar Roving Vehicles 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 Harison Schmitt.

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Each rover was used on three traverses, one per day over the three day course of each mission. On Apollo 15 the Lunar Roving Vehicle 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 Lunar Module 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 Lunar Roving Vehicle reached a distance of 4.5 km from the Lunar Module. 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 Lunar Module was 7.6 km.

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The Lunar Roving Vehicle was developed in only 17 months and yet performed all its functions on the Moon with no major anomalies. Harison Schmitt of Apollo 17 said, "....the Lunar Rover proved to be the reliable, safe and flexible lunar exploration vehicle we expected it to be. Without it, the major scientific discoveries of Apollo 15, 16, and 17 would not have been possible; and our current understanding of lunar evolution would not have been possible."

Also in this series – World's Greatest Cars, Part 1 – Donald Campbell’s Land Speed Record Bluebird.

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