Driving on the Moon
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.
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.
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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."
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