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SP-4212
- On
Mars: Exploration of the Red Planet. 1958-1978
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- INTRODUCTION
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- [xi] For many members
of the Viking flight team, the early morning hours of 20 July 1976
were the culmination of 8 years of intense activity. Several of
the scientists had more than 15 years invested in preparations for
the investigations that would begin once Viking safely landed on
the surface of Mars. The focus of everyone's attention on this day
was the Viking I spacecraft in orbit around Mars. Across 348
million kilometers, the team maintained contact with the
3250-kilogram craft from the Jet Propulsion Laboratory (JPL) in
Pasadena, California. JPL this night stood jewellike, its brightly
lit buiIdings contrasting sharply with the darkened silhouette of
the San Gabriel Mountains. Outside the Theodore von Karman
Auditorium, converted into a press center for the mission, mobile
television vans were being readied to broadcast the news of
Viking's success or failure.
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- While reporters prepared stories and
visitors strolled over the grounds, members of the flight team
could be seen on the closed-circuit television monitors as they
sat in the half-light of the control room. Elsewhere, hundreds of
engineers, scientists, technicians, and support crews were at work
or waiting to go to work. At 1:52 a.m., PDT, the audio circuit on
the JPL television came to life, and George Sands, associate
project scientist and for the moment the "Voice of Viking,"
announced: "We have separation.... We have engineering data
indicating separation....Separation is being confirmed all along
the line." Eighteen minutes 18 seconds earlier, the time it took
the confirming radio signal to travel from Mars to Earth, the
lander had separated from the orbiter. 1
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- By 2 a.m., the noise that had been
building up at the press center and in the visitor areas
diminished. Mission control, a small, glass-walled room with men
seated around a circular console watching data displayed on
television screens, was being projected on monitors around the
lab. "Beyond the controllers' desks and the consoles, through the
glass walls of his office.... [was] Jim Martin, a big man in a
short-sleeved blue shirt." James Slattin Martin, Jr., had the
bearing and appearance of a military man. His closely cropped iron
gray hair added to the image and encouraged nicknames like the
"Paratroop Colonel" and the "Prussian General." Many members of
the Viking team would attest publicly that he had run a tight
project, but even those who had cursed him under their breath over
the years had to admit that the incredible performance of the
spacecraft during its 11 -month cruise toward Mars and the normal
postseparation checkout of [xii] the lander
indicated that all the discipline and hard work Martin had put
them through had been worth it. With a billion dollars invested in
two spacecraft, someone had to have a firm grip. As the lander in
its protective aeroshell fell freely toward the surface thousands
of kilometers below it, Jim Martin listened to the controllers
reporting tersely and calmly on the latest electronic news.
2
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- At 3 a.m., Albert R. Hibbs, a senior
advanced missions planner at JPL, relieved George Sands in the
commentator's booth. Hibbs, a veteran "voice" of many earlier
unmanned spacecraft directed from Pasadena, had what one observer
called "marvelous sense of theater." Smiling, Hibbs noted that the
deorbit burn of the lander's eight small rocket motors had gone
smoothly and the spacecraft had proper velocity. Impishly, he
noted that it was also going the right direction.
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- At 2 p.m., everyone was still waiting.
Hibbs reported: "So far, everything that is supposed to have
happened ....has happened and right on schedule. We are rapidly
approaching the surface of Mars...." As the craft followed its
curved trajectory, Hibbs noted that it had only 11 340 kilometers
to go.*
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- 4:43:08 a.m. PDT. Less than 10 minutes to
touchdown, 28 minutes to confirmation. Al Hibbs informed his
audience that he and George Sands would talk the lander down, but
neither they nor anyone else at the mission center had any control
over the spacecraft at this point; they could only keep listeners
posted on the latest news. Obeying only its preprogrammed onboard
computers, the lander was "inexorably going to the surface...." By
now "the lander has felt the impact of the Martian atmosphere,
although we won't know for 19 minutes."
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- 4:53:14 a.m. PDT. Hibbs reminded the
people at JPL that "Viking should be on the surface by now, one
way or another." A steady volume of 18-minute-old data kept
flowing into the control center. The Viking team....
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- Viking Project Manager James S.
Martin, Jr., works at his desk at Jet Propulsion
Laboratory.
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- [xiii]....watched each
new data point with increasing interest. The flight path analysis
group had devised a visual display that portrayed the predicted
descent curve for the lander-a single line graph that measured the
lander's altitude against time. That line, a gentle curve sweeping
downward from left to right, ended at touchdown. Once the lander
in its aeroshell reached about 244 000 meters, the upper limits of
the Martian atmosphere, onlookers could watch on the TV monitors
as the actual path of the lander (in the form of data points) was
plotted against the predicted normal curve. That graph was the
tangible link between the watchers gathered in Pasadena and the
Viking spacecraft approaching Mars. The first data point was right
on the "nominal" curve.
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- From mission control, a disembodied voice
began calling out the velocity and altitude of the spacecraft. The
descent progressed rapidly. At 98 707 meters, the spacecraft was
traveling 4718 meters per second.
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- When Viking I reached 60 960 meters, Hibbs
suggested, "....we can now put out some of the instruments that
cannot stand the temperature of entry-pressure and temperature
sensors that have to stick out of the aeroshell. " Calling
attention to a second graph on the television screens, he said
that the viewers could watch the gravity forces "build up on that
graph. Very violent changes in the effective combination of Mars'
gravity and atmosphere on the spacecraft." In just the few seconds
that it had taken him to make that remark, the acceleration force
had increased from 2.7 times to 5 times the normal Martian
gravity. By the time the spacecraft reached 30,000 meters, the
atmosphere was beginning to exert a braking effect, slowing the
lander to only 3000 meters per second. The gravity forces
continued to rise-6.8, then 8.4, the maximum force encountered. At
27 000 meters, the velocity dropped to 1820 meters per second. As
the craft passed the 24 000 meter mark, Hibbs reported: "Well,
we're coming down. We're coming down. It's a long period of glide;
almost flat glide to get rid of some more of the speed before the
parachute comes out." From mission control, the callout of the
descent continued in a measured, emotionless tone. When the craft
passed through an altitude of 22 800 meters, it was moving at 982
meters per second. The acceleration forces had been reduced to
0.8. At 5:09:50 a.m., the parachute deployed, slowing the craft
even further, to 709 meters per second.
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- 5:11:27 p.m. PDT. 1463 meters, 54 meters
per second. At 1400 meters, the terminal descent engines started.
At 5:12:07.1 a.m. PDT July 20, a voice in mission control called
out, "Touchdown, we have touchdown!" A chorus of cheers rose for
the even t completed 19 minutes earlier on Mars. "We have several
indications of touchdown. " Mars local time was 4:13:12 p.m. when
Viking I landed on the surface.
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- Jim Martin, who had been watching the
descent curve on his monitor, stood up abruptly. He shook hands
with William H. Pickering, former director of JPL, and exchanged
congratulations with his teammates who
[xiv] rushed in to his
office. But then he paused for a moment to take another look at
the televised data, wanting to be very sure that it had actually
happened. A critical event in the life of the Viking project had
come to a successful conclusion. Controllers and support personnel
who had been quietly doing their tasks let loose with a burst of
backslapping, embracing, and handshaking. In the auditorium, a
newly opened bottle of cold duck was passed around as NASA public
affairs officers and news people shared ceremonial sips. Viking 1
was safely down on Mars. 3
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- Nick Panagakos' public affairs officer
from NASA Headquarters who had for weeks been answering questions
for the press, smiled and shook his head. Like many of his
colleagues, he had been telling people that Viking would land
safely. But now that it had actually happened, he found it hard to
believe. As the team in the control room settled back down to
prepare for the reception of the first pictures of the Martian
landscape, many persons around the Jet Propulsion Laboratory
reflected on Viking's amazing odyssey.
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- * * *
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- When NASA planetary investigators began
planning the exploration of Earth's closest neighbor, basic
elements in their strategy were dictated by common sense. The
space agency planners proposed to visit the nearest bodies
first-the moon, Mars, and Venus. They planned to conduct simple
projects initially and progress to more complex ones. Flyby
spacecraft would be sent to take photographs and measurements and,
after such basic reconnaissance had been made, heavier and more
sophisticated orbiting craft would be sent to the target of
investigation. After more detailed evaluations of the environment
had been completed, atmospheric probes- either hard-landers
(spacecraft that would crash-land) or soft-landers- would be used
for further study. Different bodies would require different
instrumentation. Photography, for instance, would not be suitable
for cloud-covered Venus; on Mars it would be an experiment with
exciting potential. During the past two decades, this
strategy-flyby, orbiter, lander-has become a formalized part of
NASA's planetary exploration program.
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- Mars, because it is reasonably close to
Earth, has been the subject of much scientific examination. The
Viking project was begun by NASA in the winter of 1968 to make
landed scientific investigation of biological, physical, and
related phenomena in the atmosphere and on the surface of Mars.
The desire to explore for possible life forms on the Red Planet
was one of the earliest goals of scientists who became part of the
United States space science program, stretching Viking's roots
back to the early 1960s. While NASA's first attempts to land craft
on Mars were successful, that success did not come without a
struggle. Chapter
1 examines the reasons
[xv] scientists wished to have a closeup look at Mars
and describes the new opportunities that opened with the coming of
space travel. As Chapter 2 indicates, the dream was not transformed into
reality until new and reliable launch vehicles became available in
the mid-1960s, but the scientific community began early to prepare
for landed investigations of the planet. Modest flyby probes such
as Mariner it, using less powerful rockets than the later
Viking's, provided new if discouraging information about Mars.
Despite initial photographic evidence that did not encourage the
search for life, a small group of biological scientists-who called
themselves exobiologists-began to develop instrumentation that
would serve as the prototypes for life detectors on spacecraft
that might fly in the future. These activities are related in
Chapter
3, while Chapter 4 deals with the plans for NASA's first Mars lander
project. Called Voyager ** and conducted by the Jet Propulsion Laboratory,
this project was ambitious, perhaps too ambitious for the times.
Expansion of the war in Vietnam and demands for federal funds for
many sectors of the American economy began a period of budget
problems for NASA. Voyager died for a complex series of reasons in
late summer 1967.
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- While budgetary stringencies were to
remain with NASA planners from that time on, enthusiasm for a Mars
lander project also continued. The focus of that spirit shifted
from JPL to the Langley Research Center. The aggressive team at
the Virginia center entered the Mars game just in time to see
Voyager terminated. Chapter 5 chronicles the Langley entry into the planetary
spacecraft business. Chapter 6 tells the story of the Viking orbiter within the
context of advanced Mariner Mars spacecraft. Jim Martin and his
colleagues, realizing that the JPL people had mastered the flyby
and orbiter trade, persuaded them to become part of the Viking
team. As Chapter
7 indicates, the Viking lander
demanded many new inventions. In addition to new and complicated
mechanical systems, it also required closely knit managerial,
technical, and scientific teams that could come together in a
cohesive organization during the data-gathering and analysis
phases of the mission.
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- Before collection of scientific
information could begin, landing sites for the craft had to be
chosen. Data obtained from the 1971 Mariner orbiter assisted the
specialists in this task but, as Chapter 8 recounts, there was considerable debate over the
best places to land, given both scientific interests and
engineering constraints. Despite the time and energy given to site
selection, Mars held some surprises for the Viking team. The first
orbiter photographs, which the team hoped would certify the
suitability of the preselected landing sites, showed extremely
hazardous terrain. Site certification, described in Chapter 9, became a renewed search for suitable and safe
areas on Mars. For nearly a month, the project members labored to
find [xvi] a safe haven for
the lander. Finding a site for the second lander was an equally
time-consuming job.
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- In Viking, NASA's most complex unmanned
space project to that date were many stories of great human effort
and some of personal sacrifice. But the scientific results were
the payoff. To have proved the technological capability to design,
build, navigate, and land a spacecraft on Mars was not enough.
Chapters 10 and 11 outline the scientific results of the Viking
investigations and examine some of the unresolved questions. As so
often is true in new fields of inquiry, as many questions were
raised as were answered. And as earlier investigations of Mars
have shown, the latest hypothesis can be upset by later, more
detailed data. The Epilogue, therefore, considers possible future
explorations of the Red Planet within the context of NASA's goals
and other national priorities. One adventure was completed, but
the exploration had just begun.
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- This book is just one of many possible
histories that could be written about the events surrounding the
Viking project. It is the official history because it was
commissioned and paid for by the National Aeronautics and Space
Administration. The authors began work shortly before Viking was
scheduled to land on 4 July 1976, and they were present in
Pasadena while Jim Martin and his team searched for a landing
site. Exposure to the site selection process allowed us to see key
project personnel at work and begin to understand the many
complexities of Viking. We decided very quickly that we could not
tell all the stories that participants might like to have told. We
also concluded that, to appreciate fully the accomplishments of
the project, readers should be exposed to the Mariner flights to
Mars and to other planned but unconsummated missions to send
landers to another planet. Thus our book evolved. In ignoring
certain aspects or in describing others only briefly, we have not
intended to slight other important aspects of the Viking effort.
There are just too many stories and too many participants for them
all to be included in this single volume.
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* Hibbs and most of
his Viking teammates used the common English measurements (miles
and feet), but the authors have used metric units in this book to
conform with NASA requirements that the système
international d'unités (SI) be used in all NASA
publicationbs.
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- ** NASA used the name
"Voyager" again later for another planetary program, in which two
spacecraft investigated Jupiter in 1979 flybys.
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