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On Mars:
Exploration of the Red Planet. 1958-1978
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- EPILOGUE
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- [421] Viking was a success, both as a
flight project and as a scientific investigation. Excellent
hardware performance was the key to a fruitful mission. Project
specifications called for a return of scientific data from the
landers for a minimum of 90 days; hut by the end of the primary
mission on 15 November 1976, at solar conjunction, Viking lander 1
had been operating on the surface for 128 days, Viking lander 2
for 73 days. After a month-long rest while Mars disappeared from
Earth's view as the planet swung behind the sun, the landers were
awakened in mid-December 1976 for the extended mission, which
lasted until 1 April 1978. The extended mission gave Viking
scientists time to collect additional data on nearly every aspect
of Mars science for which the landers had been
programmed.1
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- April and May 1978 were months of
transition for the Viking project. Under NASA management
directives, the project was transferred to the Jet Propulsion
Laboratory by the Viking staff at Langley Research Center. Old
Viking hands, like G. Calvin Broome, project manager and mission
director for the extended mission, left the project, and personnel
from JPL took their places. Kermit Watkins, recognized for his
role in preparing the Viking orbiter for flight, became project
manager for what was called the continuation mission. Viking
project scientists Gerald Soffen, who had accepted a new position
at NASA Headquarters, was replaced by Conway Snyder.
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- Original plans had called for terminating
the Viking mission after completion of the extended phase, but the
spacecraft were functioning so satisfactorily in the spring of
1977 that the agency reconsidered the request of Viking science
teams for an extension of the mission's activities. A continuation
mission also received the strong endorsement of the Science
Steering Group at its June 1977 meeting, but the major problem was
money. Mission managers would have to reduce expenditures to a
level that would continue operations without any additional funds
in fiscal 1978. Once again, everyone tightened fiscal belts, and
the project moved forward. 2
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- Hardware problems on the Viking spacecraft
began in the fall of 1977. In September, the second
traveling-wave-tube amplifier on Viking lander 2 failed, and
without this amplifier unit it could not communicate with Earth
through the orbiter. Then a gas leak developed in the attitude
control system of Viking orbiter 2, which required disabling half
the control system to prevent further propel ant loss. In February
1978, a more serious leak developed, losing about 22 percent of
the remaining gas. As [422] a third leak in March further depleted
the supply. Later that month, the flight controllers placed
orbiter 2 in a roll-drift to prevent any further problems of this
sort. Some atmospheric water observations were made by orbiter 2
in June and July, 25 July the spacecraft began to drift out of
alignment with the sun, and no propellant was left to correct its
attitude. At 6:01 a.m. UMT on 25 July 1978 (11:01 p.m. PDT, 24
July), orbiter 2 ceased operating during orbit 706-1049.5 days
after launch from Earth. 3
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- Lander 2 could communicate with Earth only
via orbiter 1, while lander 1 could make direct contact. According
to the continuation mission team, with these capabilities the
landers could continue responding until December 1978, the start
of another solar conjunction. But the scientists wanted to squeeze
still more from the hardware. Mike Carr and his colleagues on the
orbiter imaging team, the most vocal advocates of continuing the
mission, wanted to obtain more high-resolution photographs of
potential landing sites for the next Mars mission. Remembering
just how harrowing the site selection and certification process
had been for Viking, they argued that they needed to get as many
images of the surface as the hardware would permit. In addition,
they wanted to study Martian weather and atmosphere closely from
January to April 1979, because this season would be similar to the
one in which they had observed dust storms during 1977.
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- Two serious limitations affected extending
Viking any further than December 1978. Funds, of course, were
critical, as they had always been, but also the communications
loads imposed on the Deep Space Network by the Pioneer-Venus and
Voyager-Jupiter missions meant that Viking could have only a
limited amount of time on the air to transmit scientific
information from Mars to Earth. The ability of JPL's mission
control center and its Deep Space Network to squeeze the Viking
transmissions into the schedule became one of the overriding
factors in the continued life of Viking. In April 1979, Conway
Snyder, in a memorandum to all the Viking scientists, projected
that operations would come to an end in July of that year. He
noted that the mission had provided the team "with a long and
interesting road," and he was pleased that they had all been able
to travel it together. But he also suggested that the mission
might "afford us a few more surprises yet before the end."
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- The end did not come in 1979. Viking
lander 2 was shut down on 12 April 1980 after 1316.1 days on the
surface. Orbiter 1 was silenced by a command from JPL on 7 August
1980, because it, too, was about out fuel. Three of the four
spacecraft were silent, but lander 1 remained active and would
likely continue its transmissions to Earth for some years. Each
week, the team at JPL would query the spacecraft for weather
information and periodically ask for surface pictures so the
specialists could monitor the Martian landscape in front of the
lander for any changes. 6
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- Statistical evidence of success includes
51 539 orbital images of the Red Planet and more than 4500 images
from the landers. About 97 percent of the [423] planet was
photographed at a resolution of about 300 meters, while 2 percent
of the planet was seen at a resolution of 25 meters or better.
Together, the two landers returned more than 3 million weather
reports by August 1980. Total orbital infrared observations
exceeded 100 million. For generations, discussions about Mars had
included such traditional topics as canals, waves of darkening,
and blue clearings. But with NASA's explorations of Earth's near
neighbor, man had at his disposal "a plethora of hard data about
the large variety of geological features on the planet, about the
composition of the surface, the atmosphere, and the polar caps,
and about many aspects of Martian meteorology, including
temperatures, pressures, tides, dust storms, and the abundance and
transport of water vapor." Scientists, mission planners, and
hardware specialists expected to spend much of the 1980s analyzing
this information and preparing for another mission to Mars in the
1990s that would yield "as great a quantum jump in our
understanding of this complex and fascinating planet" as did
Mariner and Viking. 7
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