Multimedia Mania/abacus-multimedia-mania.iso/dp/0096/00969.txt

Text File | 1993-07-27 | 27KB | 431 lines

$Unique_ID{bob00969}
$Pretitle{}
$Title{Apollo Expeditions To The Moon
Chapter 5: Scouting The Moon}
$Subtitle{}
$Author{Cortright, Edgar M.}
$Affiliation{NASA}
$Subject{surveyor
lunar
surface
moon
apollo
first
ranger
orbiter
spacecraft
landing
see
pictures
see
figures
}
$Date{1975}
$Log{See Far Side of Moon*0096901.scf
See Surveyor*0096902.scf
}
Title:       Apollo Expeditions To The Moon
Author:      Cortright, Edgar M.
Affiliation: NASA
Date:        1975

Chapter 5: Scouting The Moon

     After centuries of studying the Moon and its motions, most astronomers
faced with diminishing returns had abandoned it to lovers and poets by the
time that Sputnik ushered in the space age.  The hardy few who had not been
wooed away to greener astronomical pastures were soon to be richly rewarded
for their patience.

     Before the invention of the telescope in 1608, astronomers had to be
content with two good eyes and a fertile imagination to surmise the nature of
the lunar surface.  As a consequence they mainly devoted themselves to the
mathematics of the Moon's motions relative to the Earth and Sun.  The early
telescopes that first revealed the crater-pocked face of the Moon touched off
several centuries of speculation about the lunar surface by scientists and
fiction writers alike - it often being unclear who was writing the fiction.
But telescopes peering through the turbulent atmosphere of Earth have severe
limitations.  By 1956 the very best terrestrial telescope images of the Moon
were only able to resolve objects about the size of the U.S. Capitol.
Anything smaller was a mystery.

     So the question remained: What was the lunar surface really like? While
few people really believed the Moon to be made of green cheese, many
scientific hypotheses cherished not long ago were equally strange and rather
more ominous.  They included deep fields of dust into which a spacecraft might
sink; a labyrinth of "fairy castles" such as children build by dripping wet
sand at the beach; electrostatic dust that might spring up and engulf an alien
object; and treacherously covered crevasses into which an unwary astronaut
might fall.  What proved to be the most accurate prediction, however, likened
the Moon to a World War I battlefield, bombarded by a rain of meteoroids
throughout the millennia, and churned into a wasteland of craters and debris.
The absence of an atmosphere and the low gravitational field would allow small
secondary particles to be blasted from the surface by a primary meteoroid
impact and thrown unimpeded halfway around the Moon.  This led to the concept
of a uniform blanket of ejecta over the entire Moon.

     But our story is getting ahead of itself.  The surface properties of the
Moon were largely unknown in 1958, a matter which assumed great practical
importance when man's first journeys to the Moon began to take shape.  How
much weight would the surface support?  What were the slopes? Were there many
rocks and of what size?  Would the dust or dirt cling?  What was the intensity
of primary and secondary meteoroid bombardment?  What was the exact size and
shape of the Moon, and what were the details of the lunar gravity field into
which our spaceships would one day plunge?

[See Far Side of Moon: Mankind's first glimpse of the far side of the Moon
came in October 1959, provided by the Soviet spacecraft Luna 3.]

A Shaky Start

     The military rockets developed in the 1950's provided a basic tool with
which it became possible to send rudimentary spacecraft to the Moon. Both the
Army and the Air Force were quick to initiate efforts to be the first to the
Moon with a manmade object.  (The Russians, as it proved, were equally quick,
or quicker.)  These first U.S. projects, which were transferred in 1958 to the
newly formed National Aeronautics and Space Administration, consisted of four
Air Force Thor-Able rockets, and two Army Juno II rockets, each with tiny
payloads, designed to measure radiation and magnetic fields near the Moon and,
in some cases, to obtain rudimentary pictures.  NASA and the Air Force then
added three Atlas-Able rockets, which could carry heavier payloads, in an
attempt to bolster these early high-risk efforts.  Of these nine early
missions launched between August 1958 and December 1960, none really
succeeded.  Two Thor-Able and all three Atlas-Able vehicles were destroyed
during launch.  One Thor-Able and one of the Juno II's did not attain
sufficient velocity to reach the Moon and fell back to Earth.  Two rockets
were left.

     The Soviets were also having problems.  But on January 4, 1959, Luna 1,
the first space vehicle to reach escape velocity, passed the Moon within about
3700 miles and went into orbit about the Sun.  Two months later the United
States repeated the feat with the last Juno II, although its miss distance was
37,300 miles.  A year later the last Thor-Able payload flew past the Moon, but
like its predecessors it yielded no new information about the surface.  On
October 7, 1959, the Soviet Luna 3 became the first spacecraft to photograph
another celestial body, radioing to Earth crude pictures of the previously
unseen far side of the Moon.  The Moon was not a "billboard in the sky" with
slatted back and props.  Its far side was found to be cratered, as might be
expected, but unlike the front there were no large mare basins.  The primitive
imagery that Luna 3 returned was the first milepost in automated scientific
exploration of other celestial bodies.

     Undaunted by initial failures, and certainly spurred on by Soviet
efforts, a NASA to plan a long-term program of lunar exploration that would
embody all necessary ingredients for success.  The National Academy of
Sciences was enlisted to  help draw the university community into the effort.
The Jet Propulsion Laboratory, a California Institute of Technology affiliate
that had been transferred from the Army to NASA in 1958, was selected to carry
out the program.  JPL was already experienced in rocketry and had participated
in the Explorer and Pioneer IV projects.

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.

[See Surveyor: The spidery Surveyor consisted of a tubular framework perched
on three shock-absorbing legs.]

     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.

     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 steerilizing 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 failed to turn on.  I will never
forget the feeling of dismay in the JPL control room that day.

     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 to us.

     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 o a man.

     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 the 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.

Testing the Surface

     Surveyor, which had been formally approved in the spring of 1960, was
originally conceived for the scientific investigation of the Moon's surface.
As in the case of the Ranger, its use was redirected according to the needs of
Apollo.

     With the proposed addition of an orbiting version of Surveyor, later to
become Lunar Orbiter, the unmanned lunar-exploration program in support of
Apollo shaped up this way: Ranger would provide us with our first look at the
surface; Surveyor would make spot checks of the mechanical properties of the
surface: and Lunar Orbiter would supply data for mapping and landing-site
selection.  The approach was sound enough, but carrying it out led us into a
jungle of development difficulties.

     Few space projects short of Apollo itself embodied the technological
audacity of Surveyor.  Its Atlas-based launch vehicle was to make use of an
entirely new upper stage, the Centaur, the world's first hydrogen-fueled
rocket.  It had been begun by the Department of Defense and later transferred
to NASA.  Surveyor itself was planned to land gently on the lunar surface, set
down softly by throttlable retrorockets under control of its own radar system.
It was to carry 350 pounds of complex scientific instruments.  Responsibility
for continuing the Centaur development was placed with the Marshall Space
Flight Center, with General Dynamics the prime contractor.  JPL took on the
task of developing the Surveyor, and the Hughes Aircraft Company won the
competition for building it.  We soon found that it was a very rough road.
Surveyor encountered a host of technical problems that caused severe schedule
slips, cost growth, and weight growth.  The Centaur fared little better.  Its
first test flight in 1962 was a failure.  Its lunar payload dropped from the
planned 2500 pounds to an estimated 1800 pounds or less - not sufficient for
Surveyor.  Its complex multi-start capability was in trouble.  Wernher von
Braun, necessarily preoccupied with the development of Saturn, recommended
cancelling Centaur and using a Saturn-Agena combination for Surveyor.

     At this point we regrouped.  Major organizational changes were made at
JPL and Hughes to improve the development and testing phases of Surveyor.
NASA management of Centaur was transferred to the Lewis Research Center under
the leader ship of Abe Silverstein, where it would no longer have to compete
with Saturn for the attention it needed to succeed.  Its initial capabilities
were targeted to the minimum required for a Surveyor mission 2150 pounds on a
lunar-intercept trajectory.  This reduced weight complicated work on an
already overweight Surveyor, and the scientific payload dropped to about 100
pounds.

     It all came to trial on May 31, 1966. when Surveyor I was launched atop
an Atlas-Centaur for the first U.S. attempt at a soft landing.  On June 2,
Surveyor I touched down with gentle perfection on a level plain in the Ocean
of Storms, Oceanus Procellarum.  A large covey of VIPs had gathered at the JPL
control center to witness the event.  One of them, Congressman Joseph E.
Karth, whose Space Science and Applications Subcommittee watched over both
Surveyor and Centaur, had been both a strong supporter and, at times, a tough
critic of the program.  The odds for success on this complex and audacious
first mission were not high.  I can still see his broad grin at the moment of
touchdown, a grin which practically lighted up his corner of the darkened
room.  We sat up most of the night watching the first of the 11,240 pictures
that Surveyor I was to transmit.

     Four months prior to Surveyor's landing, on February 3, 1966, the Russian
Luna 9 landed about 60 miles northeast of the crater Calaverius, and radioed
back to Earth the first lunar-surface pictures.  This was an eventful year in
lunar exploration, for only two months after Surveyor I, the U.S. Lunar
Orbiter I ushered in that successful and richly productive series of missions.

     Surveyor found, as had Luna before it, a barren plain pitted with
countless craters and strewn with rocks of all sizes and shapes.  No deep
layer of soft dust was found, and analysts estimated that the surface appeared
to be firm enough for both spacecraft and men.  The Surveyor camera, which was
more advanced than Luna's, showed very fine detail.  The first frame
transmitted to Earth showed a footpad and its impression on the lunar surface,
which we had preprogrammed just in case that was the only picture that could
be received.  At our first close glimpse of the disturbed lunar surface, the
material seemed to behave like moist soil or wet sand, which, of course, it
was not.  Its appearance was due to the cohesive nature of small particles in
a vacuum.

     Surveyor II tumbled during a midcourse maneuver and was lost, but on
April 19, 1967, Surveyor III made a bumpy landing inside a 650-foot crater in
the eastern part of the Sea of Clouds.  Its landing rockets had failed to cut
off and it skittered down the inner slope of a crater before coming to rest.
Unlike its predecessors, Surveyor III carried a remotely controlled device
that could dig the surface.  During the course of digging, experimenters
dropped a shovelful of lunar material on a footpad to examine it more closely.
When Surveyor III was visited by the Apollo 12 astronauts 30 months later in
1970, the little pile was totally undisturbed, as can be seen in the
photograph reproduced at the beginning of Chapter 12.

     The historic rendezvous of Apollo 12 with Surveyor III would never have
been possible without the patient detective work of Ewen Whitaker of the
University of Arizona.  The difficulty was that the landing site of Surveyor
was not precisely known.  Using Surveyor pictures of the inside of the crater
in which it had landed, Whitaker compared surface details with details visible
in Orbiter photographs of the general area that had been taken before the
Surveyor landing.  He eventually found a 650- foot crater that matched, and
concluded that that was where Surveyor must be.  Thus the uncertainty in
Surveyor's location was reduced from several miles down to a single crater.
By using Orbiter photographs as a guide, Apollo 12 was able to fly down a
"cratered trail" to a landing only 600 feet away from Surveyor.

     Surveyor IV failed just minutes before touchdown, but the last three
Surveyors were successful.  On September 10, 1967, Surveyor V landed on the
steep inner slopes of a 30 by 40 foot crater on Mare Tranquillitatis.  It
carried a new instrument, an alpha backscattering device developed by Anthony
Turkevich of the University of Chicago.  With this device he was able to make
a fairly precise analysis of the chemical composition of the lunar-surface
material, which he correctly identified as resembling terrestrial basalts.
This conclusion was also supported by the manner in which lunar material
adhered to several carefully calibrated magnets on Surveyor.  Two days after
landing, Surveyor V's engines were reignited briefly to see what effect they
would have on the lunar surface. The small amounts of erosion indicated that
this would pose no real problem for Apollo, though perhaps causing some loss
of visibility just before touchdown.

     Surveyor VI checked out still another possible Apollo site in Sinus
Medii.  The rocket-effects experiment was repeated and this time the Surveyor
was "flown" to a new location approximately 8 feet from the original landing
point.  Some of the soil thrown out by the rockets stuck to the photographic
target on the antenna boom, as shown in the picture on page 88.

     The last Surveyor was landed in a highland area just north of the crater
Tycho on January 9, 1968.  A panoramic picture of this ejecta field taken by
Surveyor VII is shown on page 91 as well as a mosaic of its surface
"gardening" area.  I remember walking into the control room at JPL at the
moment the experimenters were attempting to free the backscatter instrument,
which had hung up during deployment.  Commands were sent to the surface
sampler to press down on it.  The delicate operation was being monitored and
guided with Surveyor's television camera.  When I started asking questions,
Dr. Ron Scott of Cal Tech crisply reminded me that at the moment they were
"quite busy." I held my questions and they got the stuck instrument down to
the surface.  It seemed almost unreal to be remotely repairing a spacecraft on
the Moon some quarter of a million miles away.

     Before the launch of Surveyor I, in the period when we faced cost
overruns and deep technical concerns, NASA and JPL had pressed the Hughes
Aircraft Company to accept a contract modification that would give up some
profit already earned in favor of increased fee opportunities in the event of
mission successes.  They accepted, and this courageous decision paid off for
both parties.  NASA of course was delighted with five out of seven Surveyor
successes.

Mapping and Site Selection

     Meanwhile the third member of the automated lunar exploration team had
already completed its work.  The fifth and last Lunar Orbiter had been
launched on August 1, 1967, nearly half a year earlier.  When JPL and Hughes
began to experience difficulties with Surveyor development, and with the
Centaur in deep trouble, NASA decided to back up the entire program with a
different team and different hardware.  The Surveyor Orbiter concept was
scrapped, and NASA's Langley Research Center was directed to plan and carry
out a new Lunar Orbiter program, based on the less risky Atlas-Agena D launch
vehicle.  Langley prepared the necessary specifications and Boeing won the
job.  Boeing's proposed design was beautifully straightforward except for one
feature, the camera.  Instead of being all-electronic as were prior space
cameras, the Eastman Kodak camera for the Lunar Orbiter made use of 70-mm film
developed on board the spacecraft and then optically scanned and telemetered
to Earth.  Low-speed film had to be used so as not to be fogged by space
radiation.  This in turn required the formidable added complexity of
image-motion compensation during the instant of exposure. Theoretically,
objects as small as three feet could be seen from 30 nautical miles above the
surface.  If all worked well, this system could provide the quality required
for Apollo, but it was tricky, and it barely made it to the launch pad in time
to avoid rescheduling.

     The Orbiter missions were designed to photograph all possible Apollo
landing sites, to measure meteoroid flux around the Moon, and to determine the
lunar gravity field precisely, from accurate tracking of the spacecraft.
Orbiter did all these things and more.  As the primary objectives for Apollo
program were essentially accomplished on completion of the third mission, the
fourth and fifth missions were devoted largely to broader, scientific
objectives - photography of the entire lunar near side during Mission IV and
photography of 36 areas of particular scientific interest on the near side
during Mission V.  In addition, 99 percent of the far side was photographed in
more detail than Earth-based telescopes had previously photographed the front.

     The first Lunar Orbiter spacecraft was launched on August 10, 1966, and
photographed nine primary and seven secondary sites that were candidates for
Apollo landings.  The medium-resolution pictures were of good quality, but a
malfunction in the synchronization of the shutter caused loss of the
high-resolution frames.  In addition, some views of the far side and oblique
views of the Earth and Moon were also taken (see page 78).  When we made the
suggestion of taking this "Earthrise" picture, Boeing's project manager, Bob
Helberg, reminded NASA that the spacecraft maneuver required constituted a
risk that could jeopardize the company profit, which was tied to mission
success.  He then made the gutsy decision to go ahead anyway and we got this
historic photograph.

     The next two Lunar Orbiter missions were launched on November 6, 1966,
and February 4, 1967.  They provided excellent coverage of all 20 potential
Apollo landing sites, additional coverage of the far side and other lunar
features of scientific interest, and many oblique views of lunar terrain as it
might be seen by an orbiting astronaut.  One of these was a dramatic oblique
photograph of the crater Copernicus, which NASA's Associate Administrator, Dr.
Robert C. Seamans, unveiled at a professional society conference in Boston and
which drew a standing ovation and designation as 'picture of the year." Among
the possible Apollo sites photographed by Orbiter III was the landing site of
Surveyor I.  Careful photographic detective work found the shining Surveyor
and its dark shadow among the myriad craters.

     The Apollo site surveys yielded surprises.  Some sites that had looked
promising in Earth-based photography were totally unacceptable.  No sites were
found to be as free of craters as had been originally specified for Apollo, so
the Langley lunar landing facility was modified to give astronauts practice at
crater dodging.  Since the basic Apollo photographic requirements were
essentially satisfied by the first three flights, the last two Orbiters
launched on May 4 and August 1, 1967, were placed in high near-polar orbits
from which they completed coverage of virtually the entire lunar surface.

     The other Orbiter experiments were also productive.  No unexpected levels
of radiation or meteoroids were found to offer a threat to astronaut safety.
Studies of the Orbiter motion, however, revealed relatively large
gravitational variations due to buried mass concentrations - the phrase was
soon telescoped to "mascons" - in the Moon's interior.  This alerted Apollo
planners to account properly for mascon perturbations when calculating precise
Apollo trajectories.

     With the completion of the Ranger, Surveyor, and Orbiter programs, the
job of automated spacecraft in scouting the way for Apollo was done.  Our
confidence was high that few unpleasant surprises would wait our Apollo
astronauts on the lunar surface.  The standard now passed from automated
machinery to hands of flesh and blood.