Mission Information
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MISSION_NAME |
VIKING
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MISSION_ALIAS |
VIKING75
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MISSION_START_DATE |
1968-01-01T12:00:00.000Z
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MISSION_STOP_DATE |
1982-01-01T12:00:00.000Z
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MISSION_DESCRIPTION |
Mission Overview
================
The Viking mission to Mars consisted of four spacecraft: the
two orbiters VO1 and VO2, and the landers VL1 and VL2
[SOFFEN1977]. During cruise to Mars the landers were attached
to the orbiters; the combined spacecraft were then known as
Viking 1 and 2. The role of the orbiters was to transport the
landers to Mars, to carry reconnaissance instruments for
certifying the landing sites, to act as relay stations for
lander data, and to perform their own scientific
investigations. The initial orbit periapses were placed over
the candidate landing sites to allow for maximum viewing
resolution and relay of the lander data. After the primary
lander missions were completed, the orbiters' orbits were
allowed to drift so that the entire planetary surface could be
systematically mapped by the three remote sensing experiments.
The Viking 1 spacecraft was launched August 20, 1975, and
arrived at Mars on June 19, 1976. Lander 1 was deployed to the
Mars surface on July 20, 1976. The VO1 orbital inclination of
38-39 degrees was chosen to optimize communication with VL1.
Viking 2 was launched September 9, 1975 and arrived at Mars
August 7, 1976. VL2 landed on September 3, 1976, at a more
northerly site than VL1. The VO2 orbit was correspondingly
more inclined than VO1; initially 55 degrees, it was later
adjusted to 80 degrees, providing particularly good coverage
of polar regions. The areocentric locations of VL1 and VL2
have since been determined to be (22.270N, 48.264W) and
(47.669N, 226.032W), respectively [YODER&STANDISH1997].
Mission Phases
==============
The timeline for the Viking Mission is divided into a number of
mission phases in terms of the types of observations and level
of activity. The references [SNYDER1977], [SNYDER1979],
[MOOREETAL1987], and [SNYDER&MOROZ1992] provide detailed
descriptions of these mission phases. A summary of the mission
phases and the relevant dates are described below. Before Mars
encounter and orbit insertion the orbiter and lander spacecraft
are considered as one spacecraft with the same mission phases.
The primary missions for all four spacecraft (VL1, VO1, VL2,
and VO2) are listed separately because each has a different
starting date. All mission phases after the primary mission
are listed only once because all four spacecraft operated
together.
VIKING 1 MARS LAUNCH
--------------------
The Viking 1 spacecraft was launched on August 20, 1975 on a
Titan Centaur 3 booster from Cape Canaveral, Florida.
Spacecraft Id: : VO1, VL1
Target Name : MARS
Mission Phase Start Time : 1975-08-20
Mission Phase Stop Time : 1975-08-20
Spacecraft Operations Type : ORBITER, LANDER
VIKING 1 MARS CRUISE
--------------------
The Viking 1 spacecraft, consisting of the VO1 orbiter and
VL1 lander, cruised to Mars for about 10 months, during which
time the spacecraft was checked periodically.
Spacecraft Id: : VO1, VL1
Target Name : MARS
Mission Phase Start Time : 1975-08-20
Mission Phase Stop Time : 1976-06-19
Spacecraft Operations Type : ORBITER, LANDER
VIKING 2 MARS LAUNCH
--------------------
The Viking 2 spacecraft was launched on September 9, 1975 on
a Titan Centaur 3 booster from Cape Canaveral, Florida.
Spacecraft Id: : VO2, VL2
Target Name : MARS
Mission Phase Start Time : 1975-09-09
Mission Phase Stop Time : 1975-09-09
Spacecraft Operations Type : ORBITER, LANDER
VIKING 2 MARS CRUISE
--------------------
The Viking 2 spacecraft, consisting of the VO2 orbiter and
VL2 lander, cruised to Mars for about 11 months, during which
time the spacecraft was checked periodically.
Spacecraft Id: : VO2, VL2
Target Name : MARS
Mission Phase Start Time : 1975-09-09
Mission Phase Stop Time : 1976-08-07
Spacecraft Operations Type : ORBITER, LANDER
VIKING ORBITER 1 PRIMARY MISSION
--------------------------------
The Viking Orbiter 1 spacecraft entered Mars orbit on June
19, 1976. Operations commenced by supporting the selection
of a landing site for VL1. Throughout the Primary Mission,
the VO1 spacecraft supported communications with the landers
and made observations of the Martian surface and atmosphere.
The Primary Mission ended at the start of the solar
conjunction in November, 1976.
Spacecraft Id: : VO1
Target Name : MARS
Mission Phase Start Time : 1976-06-19
Mission Phase Stop Time : 1976-11-15
Spacecraft Operations Type : ORBITER
VIKING LANDER 1 PRIMARY MISSION
-------------------------------
The Viking Lander 1 spacecraft separated from the VO1 orbiter
and descended to the Martian surface on July 20, 1976. The
Primary Mission focused on the collection and analysis of
soil samples and the characterization of the landing site and
atmosphere. The Primary Mission ended at the start of the
solar conjunction in November, 1976.
Spacecraft Id: : VL1
Target Name : MARS
Mission Phase Start Time : 1976-07-20
Mission Phase Stop Time : 1976-11-15
Spacecraft Operations Type : LANDER
VIKING ORBITER 2 PRIMARY MISSION
--------------------------------
The Viking Orbiter 2 spacecraft entered Mars orbit on August
7, 1976. Operations commenced by supporting the selection of
a landing site for VL2. Throughout the Primary Mission, the
VO2 spacecraft supported communications with the landers and
made observations of the Martian surface and atmosphere. The
Primary Mission ended at the start of the solar conjunction
in November, 1976.
Spacecraft Id: : VO2
Target Name : MARS
Mission Phase Start Time : 1976-08-07
Mission Phase Stop Time : 1976-11-15
Spacecraft Operations Type : ORBITER
VIKING LANDER 2 PRIMARY MISSION
-------------------------------
The Viking Lander 2 spacecraft separated from the VO2 orbiter
and descended to the Martian surface on September 3, 1976.
The Primary Mission focused on the collection and analysis of
soil samples and the characterization of the landing site and
atmosphere. The Primary Mission ended at the start of the
solar conjunction in November, 1976.
Spacecraft Id: : VL2
Target Name : MARS
Mission Phase Start Time : 1976-09-03
Mission Phase Stop Time : 1976-11-15
Spacecraft Operations Type : LANDER
VIKING EXTENDED MISSION
-----------------------
The Viking Extended Mission began after solar conjunction.
The two orbiters continued to observe the surface and
atmosphere of Mars. The two lander spacecraft analyzed
additional soil samples and dug three deep holes in the
surface. All four spacecraft monitored the planet through
the cycle of seasons. During the winter season, the landers
operated in an automatic manner designed to allow the
spacecraft to survive the cold temperatures and still return
some data.
Spacecraft Id: : VO1, VL1, VO2, VL2
Target Name : MARS
Mission Phase Start Time : 1976-11-15
Mission Phase Stop Time : 1978-05-31
Spacecraft Operations Type : ORBITER, LANDER
VIKING CONTINUATION MISSION
---------------------------
Primary objectives of the Continuation Mission were to make
orbital observations at times of the Mars year that were
missed due to landing site selection and solar conjunction
and to collect high resolution surface images when the
atmosphere was clear. A radio science solar conjunction
relativity experiment was also done during the Continuation
Mission. Lander activities consisted of measurements by the
imaging, meteorology, and XRFS instruments operating in a
fully automated manner. Viking Orbiter 2 developed a leak in
its propulsion system and lost its attitude control gas. VO2
was turned off on July 25, 1978 after 706 orbits around Mars.
Spacecraft Id: : VO1, VL1, VO2, VL2
Target Name : MARS
Mission Phase Start Time : 1978-05-25
Mission Phase Stop Time : 1979-02-26
Spacecraft Operations Type : ORBITER, LANDER
VIKING INTERIM PERIOD
---------------------
The Interim Period mission phase occurred during the time of
the Voyager 2 encounter with Jupiter. Thus, communications
to and from the Viking spacecraft were limited. The landers
continued to operate in an automated manner making imaging
and meteorology observations. A final VL2 surface sampler
sequence was conducted during this mission phase as an
engineering test in the cold temperatures of mid winter.
Orbital data stored on spacecraft tape recorders and not
returned during the Continuation Mission were downlinked
during the Interim Period.
Spacecraft Id: : VO1, VL1, VL2
Target Name : MARS
Mission Phase Start Time : 1979-02-26
Mission Phase Stop Time : 1979-07-19
Spacecraft Operations Type : ORBITER, LANDER
VIKING SURVEY MISSION
---------------------
The prime scientific objective for VO1 during the Survey
Mission was to obtain high resolution images of possible
future landing sites. The plan for the landers was to
collect image and meteorology data for as long as possible.
Because VL2 no longer had a direct downlink capability, it
meant that VL2 could return data only as long as VO1 provided
a relay link, once every seven weeks. Communications with
VL2 ended on April 11, 1980 after its batteries could no
longer hold a charge. VL2 operated on the surface of Mars
for 1281 sols. VO1 consumed the last of its attitude control
gas on August 7, 1980 and was turned off after 1485 orbits
around Mars.
Spacecraft Id: : VO1, VL1, VL2
Target Name : MARS
Mission Phase Start Time : 1979-07-19
Mission Phase Stop Time : 1980-08-07
Spacecraft Operations Type : ORBITER, LANDER
VIKING COMPLETION MISSION
-------------------------
Viking Lander 1 continued to operated in its automatic mode
during the Completion Mission. The observation sequences
were cyclic. VL1 returned via direct downlink image and
meteorology data about once a week with image sequences
repeating every 37 sols. The VL1 high-gain antenna was
programmed to track the Earth until December, 1994. However,
communications were lost in November 1982 after a command
sequence uplink.
Spacecraft Id: : VL1
Target Name : MARS
Mission Phase Start Time : 1980-08-07
Mission Phase Stop Time : 1982-11-19
Spacecraft Operations Type : LANDER
|
MISSION_OBJECTIVES_SUMMARY |
Mission Objectives Overview
===========================
Exploration of Mars, and the Viking Mission in particular, has
been part of a larger quest -- the search for better
understanding of the formation and history of the solar system.
For Mars, the specific objectives have included:
1) evolution and current structure of its interior;
2) characteristics of the surface, including its chemistry
and physical nature;
3) evolution and current composition and structure of its
atmosphere;
4) nature of the climate, including controls on both daily
and seasonal variations;
5) whether life is, or ever has been, present.
Although most Viking investigations could be defended on one or
more of the first four objectives, virtually all secondarily
addressed the fifth. On the other hand, the investigations
which focused primarily on objective #5 barely scratched the
surface of that single question; the nature of life -- and
especially its expression on another planet -- is not well
understood. According to [SOFFEN1977], 'It was finally decided
to send a set of biological tests that range in their
environmental setting from a totally aqueous milieu, rich in
organics, to a Marslike environment with no water or any other
additives. Even so, only a very narrow set of all
possibilities could be tested on the small samples
acquired ...'.
The Viking investigations and their primary objectives are
summarized in the paragraphs below. More information is
available in [SOFFEN1977], [SNYDER1977], [SNYDER1979], and
[SNYDER&MOROZ1992].
Orbiter Imaging
---------------
An early objective was assisting in landing site selection
and certification. Once the landers were safely in place,
the Orbiter imaging system was used to provide a geologic
context for the surface observations. Globally, images were
collected to provide high-resolution mosaics and maps at
resolutions approaching 100 meters. Stereo pairs of images
could be used to derive local topography; photoclinometry
could be used on single images to derive elevations and
slopes at lower accuracy. Images were also used to infer
the origin and history of major terrain types, including
disruptive events such as apparent catastrophic floods.
Crater morphologies which suggest a permafrost layer pointed
toward complex interactions of regolith and atmosphere.
The Orbiter imaging system was also used to monitor
atmospheric changes including clouds, hazes, and suspended
particles. Images of the satellites Phobos and Deimos
showed their surfaces from distances as close as 100 km.
Mars Atmospheric Water Detector (MAWD)
--------------------------------------
MAWD was designed to measure the water vapor content of the
atmosphere from orbit. Patterns were sought as a function
of local time, season, latitude, and elevation. Objectives
of the investigation included better understanding of both
diurnal and seasonal transport of water vapor as well as
location of sources and sinks.
Infrared Thermal Mapping (IRTM)
-------------------------------
IRTM measured reflections and emissions in several infrared
bands from orbit. These data could be used to infer the
physical properties of surface materials including the
relative proportions of rock, sand, and dust. Apparent
surface temperatures were used to infer the composition of
polar ices, assisting in development of atmospheric
circulation models.
Radio Science
-------------
Radio tracking of the Landers allowed determination of their
positions on the surface, the planetary rotation axis, the
spin rate, and moment of inertia. Tracking of the Orbiters
allowed determination of a gravity field for Mars. Radio
occultations yielded planetary radii and atmospheric
temperature-pressure profiles at dozens of locations. Radio
observations were also conducted to measure structure in the
solar corona and to test a prediction of general relativity
associated with passage of the radio path through the Sun's
gravitational field.
Entry Science
-------------
During descent each landing module measured both the physical
structure and chemical composition of the atmosphere. The
composition of the ionosphere allowed inference of dominant
reactions. At lower altitudes isotopic ratios could be used
to infer age of the atmosphere and an earlier composition.
Measurements such as mean molecular weight, density profile,
and composition near the surface could be used to interpret
measurements from other instruments. Measurements at
different altitudes could be used to determine how well the
atmosphere was mixed.
Lander Imaging
--------------
Lander images were used to select samples for testing in the
biology and physical properties investigations; they were also
used to select sites for experiments using the sampler arm.
Images recorded trenches that were dug, rocks that were
overturned, footpads that penetrated the surface, and magnets
that were covered by iron-bearing loose material. Images were
used to determine the distribution and appearance of rocks
and other materials near the landing sites, leading to
improved understanding of both the local area and its
history. Images of the atmosphere were used to estimate the
opacity due to suspended particles; images of materials at
the site were used to infer wind stress and rates of erosion.
One unfulfilled objective of Lander imaging was detection of
signs of life at each site.
Physical and Magnetic Properties
--------------------------------
The sampler arm and sample collector on each Lander were
used in conjunction with the Lander imaging system to
determine density, cohesion, and other physical properties
of the surface material. Repeated failure to collect rocks
in the 1 cm size range suggested they are scarce, which has
implications for creation and destruction of material in
that size range. Visual evidence that magnets were
saturated was important in estimating the concentration and
state of iron in surface particles.
Seismology
----------
The objectives of the Lander seismology investigation were
to detect seismic events or to set limits on the activity
level of Mars compared with Earth. One local event was
detected at VL2, allowing estimation of crustal thickness
and damping. In practice the seismology investigation
supported the meteorology investigation since most seismic
signals turned out to be caused by wind.
Meteorology
-----------
The Lander meteorology investigation sought to characterize
local atmospheric conditions; those in turn would constrain
global models. Diurnal and seasonal trends were sought;
effects of dust storms were also measured.
Inorganic Chemistry
-------------------
Elemental compositions of soils at each Lander site were
determined using X-Ray Flourescence Spectrometers. Results
were to be compared with compositions of terrestrial analogs
but were found to be 'dissimilar to any single known mineral
or rock type' [TOULMINETAL1977]. With addition of physical
properties, the recent history of duricrust could be inferred.
The fact that these materials were very similar at the two
Landing sites can be used in modeling transport of dust and
other small diameter particles.
Molecular Analysis
------------------
The Gas Chromatograph Mass Spectrometer gave composition of
the atmosphere at each landing site; the result was
consistent with the entry science composition. Isotope ratios
were used to infer the amount of outgassing and, from that,
the volume of volatiles which may have been lost from Mars
over geologic time. Surface samples were analyzed in an
attempt to detect organics and to measure the amount of water
present. Both are questions important in the search for life.
Biology
-------
The original objectives of the Lander biology experiment were
to detect presumed Martian life forms by their release of
metabolic products upon addition of heat, water, a dilute
aqueous solution of simple nutrients, and a concentrated
mixture of many organic compounds. After sudden and
surprising positive results, which were not consistent with
expectations or with other observations, the objectives were
expanded to include abiotic interpretations.
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REFERENCE_DESCRIPTION |
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