INSTRUMENT_HOST_DESC |
Instrument Host Overview
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The two Viking Lander spacecraft were the first spacecraft to
operate successfully for an extended period of time on the
surface of Mars. Both spacecraft operated from 1976 through
April 1980 and Viking Lander 1 (VL1) continued to operate until
November 1982. In 1981, Viking Lander 1 was renamed the Thomas
A. Mutch Memorial Station in honor of Tim Mutch, Lander
Imaging Team Leader and later NASA Associate Administrator for
Space Sciences. Tim Mutch was killed in a climbing accident in
1980.
The Viking Landers were identical to each other and had the
same instrument packages. The main lander structure was a
hexagonal prism body that housed the spacecraft computers, tape
recorder, batteries, several science instruments, and controls
for the surface sampler, thermal system, and data handling
system. The spacecraft body was supported above the surface by
three legs, each with a curved footpad. The legs were arranged
in a triangle pattern with two at the front of the lander and
one at the rear. Mounted to the sides of the spacecraft were
three terminal descent engines, two propellant tanks, and the
extendible surface sampler arm and collector head. Also
mounted on the spacecraft body were two cameras, two
radioisotope thermoelectric generators (RTG) with covers,
sample entry ports for the biology, organic chemistry and
inorganic chemistry instruments, the seismometer, the
meteorology boom, a magnifying mirror, and three imaging
reference test charts. The spacecraft had three antennas for
communications; a high-gain S-band antenna (the large disk
antenna), a low-gain S-band antenna, and a UHF antenna. The
two S-band antennas were used to communicate with Earth,
whereas the UHF antenna communicated with the orbiters. The
spacecraft had several redundant systems for computers,
batteries, and communication systems [MOOREETAL1987].
The lander was about 1.5 m across. Clearance between the
spacecraft body and the surface was about 22 cm. After landing
the spacecraft weighted about 610 kg. Power for the spacecraft
was generated by the two RTGs in which plutonium-238 produced
about 70 watts of electric power and also charged a series of
batteries. Excess heat from the RTGs was used to heat the
instruments and control systems in the spacecraft body
[SOFFEN1977].
Science Packages
================
Lander science packages included eight investigations. The
imaging system included two identical facsimile cameras. The
meteorology package was mounted on a mast and had instruments
to measure atmospheric temperature, pressure, and wind speed
and direction. Each lander had a three-axis, short-period
seismometer to measure Mars seismic activity. The seismometer
on VL1 failed to deploy and no data was returned from it, while
the one on VL2 operated as planned. A X-ray fluorescence
spectrometer (XRFS) measured the inorganic elemental
composition of soils at the landing sites. A gas chromatograph
mass spectrometer (GCMS) measured the composition of the
atmosphere and searched for organic compounds in the soils.
The biology investigation consisted of three experiments to
search for biological metabolism, growth, or photosynthesis:
carbon assimilation, labeled release of carbon-14, and gas
exchange. The physical properties investigation used
information from many lander operations, such as sampling
activities, digging trenches, pushing rocks, forming soil
piles, and footpad penetration during landing to characterize
the properties of rocks and soils at the landing sites. The
magnetic properties experiment was the only Viking experiment
to directly study the mineralogy of soils. This experiment
consisted of magnets mounted on the surface sampler collector
head and on the lander deck to collect magnetic minerals.
Finally, lander communication systems were used for radio
science experiments [SNYDER&MOROZ1992].
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