Apollo Expeditions to the Moon|
OUR FIRST CLOSE LOOK
The first project to emerge from this government/university team was named
Ranger, to connote the exploration of new frontiers. Subsequently Surveyor and Prospector
echoed this naming theme. (Planetary missions adopted nautical names such as
Mariner, Voyager, and Viking.) The guideline instructions furnished JPL for Ranger
read in part: "The lunar reconnaissance mission has been selected with the major
objective . . . being the collection of data for use in an integrated lunar-exploration
program. . . . The [photographic] system should have an overall resolution of sufficient
capability for it to be possible to detect lunar details whose characteristic dimension is
as little as 10 feet." Achieving this goal did not come about easily.
The Surveyor mission had been conceived in 1959 as
a scheme to soft-land scientific instruments an the
Moon's surface. It was a highly ambitious plan that
required both development of a radical new launch
vehicle and the new technology of a closed-loop,
radar-controlled automated landing. The cutaway
drawing shows the Atlas-Centaur launch vehicle.
The Atlas-Centaur, a major step forward in rocket propulsion,
was the first launch vehicle to use the high-energy
propellant combination of hydrogen and oxygen. Its
new Centaur upper stage, built by General Dynamics,
had two Pratt & Whitney RL-10 engines of 15,000-lb thrust each.
The first stage was a modified Atlas D
having enlarged tanks and increased thrust.
The main events in a successful Surveyor
The initial choice of launch vehicle for the Ranger was the USAF Atlas, mated
with a new upper stage to be developed by JPL, the Vega. Subsequently NASA cancelled
the Vega in favor of an equivalent vehicle already under development by the
Air Force, the Agena. This left JPL free to concentrate on the Ranger. The spacecraft
design that evolved was very ambitious for its day, incorporating solar power, full
three-axis stabilization, and advanced communications. Clearly JPL also had its eye on
the planets in formulating this design.
The spidery Surveyor consisted of a tubular framework perched an three shock-absorbing
footpads. Despite ist queer appearance, it incorporated some of the most sophisticated
automatic systems man had ever hurled into space (see specifications below). The first one
launched made a perfect soft landing an the Moon, radioing back to Earth a rich trove of
imagery and data. Seven were launched in all; one tumbled during course correction,
one went mysteriously mute during
landing, and the remaining five were unqualified successes.
Weight at launch 2193 lb
Landed weight 625 lb
Solar panel: 90 watts
Batteries: 230 ampere-hours
Dual transmitters: 10 watts each
|GUIDANCE AND CONTROL
Inertial reference: 3-axis gyros
Celestial reference: Sun and Canopus sensors
Attitude control: cold gas jets
Terminal landing: automated closed loop, with radar altimeter and doppler velocity sensor
Main retrorocket: 9000-lb solid fuel
Vernier retrorockets: throttable between 30- and 102-lb thrust each
Focal length: 25 or 100 mm
Aperture: f/4 to f/22
Resolution: 1 mm at 4 m
Typical Surveyor Specifications|
Its insectlike shadow was photographed by Surveyor I on the desolate surface of Oceanus
Procellarum. During the long lunar day it shot 10,386 pictures, including the 52 in this mosaic.
The noon temperature of 235° F dropped to 250° below zero an hour after the Sun went down.
Of a total of nine Rangers launched between 1961 and 1965, only the last three
succeeded. From the six failures we learned many lessons the hard way. Early in the
program, an attempt was made to protect the Moon from earthly contamination by
sterilizing the spacecraft in an oven. This technique, which is now being used on the
Mars/Viking spacecraft, had to be abandoned at that time when it wreaked havoc
with Ranger's electronic subsystems.
In the first two launches in 1961 the new Agena B upper stage failed to propel
the Ranger out of Earth orbit. Failures in both the launch vehicle and spacecraft misdirected
the third flight. On the fourth flight the spacecraft computer and sequencer
malfunctioned. And on the fifth flight a failure occurred in the Ranger power system.
The U.S. string of lunar missions with little or no success had reached fourteen. Critics
were clamoring that Ranger was a "shoot and hope" project. NASA convened a failure
review board, and its studies uncovered weaknesses in both the design and testing of
Ranger. Redundancy was added to electronic circuits and test procedures were tightened.
As payload Ranger VI carried a battery of six television cameras to record surface
details during the final moments before impact. When it was launched on January
30, 1964, we had high confidence of success. Everything seemed to work perfectly.
But when the spacecraft plunged to the lunar surface, precisely on target, its cameras
f ailed to turn on. I will never forget the feeling of dismay in the JPL control room that
The first lunar soft landing was accomplished
by Russia's Luna 9 on February 3, 1966, about
60 miles northeast of the crater Calaverius.
Its pictures showed details down to a tenth of
an inch five feet away. They indicated no
loose dust layer, both rounded and angular
rock fragments, numerous small craters, some
with slope angles exceeding 40 degrees, and
generally granular surface material. These
results increased confidence that the Moon was
not dangerously soft for a manned landing.
Surveyor I televised excellent pictures of the depth of the
depression in the lunar soil made by its footpad when
it soft-landed on June 2, 1966, four months after Luna 9.
Calculations from these and similar images set at rest
anxieties about the load-bearing adequacy of the Moon.
Some scientists had theorized that astronauts could be
engulfed in dangerously deep dust layers, but Surveyor's
footpad pictures, as well as the digging done by the
motorized scoop on board, indicated that the Moon would
readily support the LM and its astronauts.
But we all knew we were finally close. Careful detective work with the telemetry
records identified the most probable cause as inadvertent turn-on of the TV transmitter
while Ranger was still in the Earth's atmosphere, whereupon arcing destroyed
the system. The fix was relatively simple, although it delayed the program for three
months. On July 28, 1964, Ranger VII was launched on what proved to be a perfect
mission. Eighteen minutes before impact in Oceanus Procellarum, or Ocean of Storms,
the cameras began transmitting the first of 4316 excellent pictures of the surface.
The final frame was taken only 1400 feet above the surface and revealed details down
to about 3 feet in size. It was a breathless group of men that waited the arrival of the
first quick prints in the office of Bill Pickering, JPL's Director. The prints had not
been enhanced and it was hard to see the detail because of lack of contrast. But those
muddy little pictures with their ubiquitous craters seemed breathtakingly beautiful
By the time of the Ranger VII launch, the Apollo program had already been
underway for three years, and Ranger had been configured and targeted to scout possible
landing sites. Thus Ranger VIII was flown to a flat area in the Sea of Tranquility
where it found terrain similar to that in the Ocean of Storms: gently sloping plains
but craters everywhere. It began to look as if the early Apollo requirement of a relatively
large craterless area would be difficult to find. As far as surface properties were
concerned, the Ranger could contribute little to the scientific controversy raging over
whether the Moon would support the weight of a machine - or a man.
Like a tiny back hoe, the surface sampler fitted to some
Surveyors could dig trenches in the lunar soil. Above,
the smooth vertical wall left by the scoop indicated the
cohesiveness of the fine lunar material. Variations in
the amount of current drawn by the sampler motor gave
indication of the digging effort needed. At left above,
the sampler is shown coming to the rescue when the
head of the alpha-scattering instrument failed to deploy
on command. After two gentle downward nudges from
the scoop, the instrument dropped to the surface.
"A dinosaur's skull" was the joking name that
Surveyor I controllers used for this rock. Geologists
on the team were more solemn: "A rock
about 13 feet away, 12 by 18 inches, subangular
in shape with many facets slightly rounded.
Lighter parts of the rock have charper features,
suggesting greater resistance to erosion."
Surveyor VI hopped under its own power to a second
site about eight feet from its landing spot. This maneuver
made it possible to study the effect of firing rocket engines
that impinged an the lunar surface. Picture at left
below shows a photometric chart attached to an omni-antenna,
which was clean after first landing. Afterward,
the chart was coated with an adhering layer of fine soil
blasted out of the lunar surface.
To get maximum resolution of surface details, it was necessary to rotate Ranger
so that the cameras looked precisely along the flight path. This was not done on Ranger
VII in order to avoid the risk of sending extra commands to the attitude-control system.
I recall that on Ranger VIII JPL requested permission to make the final maneuver.
NASA denied permission - we were still unwilling, after the long string of failures,
to take the slightest additional risk. It was not until Ranger IX that JPL made tbe
maneuver and achieved resolution approaching 1 foot in the last frame. This final
Ranger, launched on March 21, 1965, was dedicated to lunar science rather than to
reconnaissance of Apollo landing sites. It returned 5814 photographs of the crater
Alphonsus, again showing craters within craters, and some rocks. Despite its dismal
beginnings the Ranger program was thus concluded on a note of success. Proposed
follow-on missions were cancelled in favor of upcoming Surveyor and Orbiter missions,
whose development had been proceeding concurrently.