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Viking (1975-1983) Pioneer | Mariner | Viking | Voyager | Magellan | Pathfinder | Galileo | Mars Global Surveyor
Overview The Viking mission consisted of two craft, Viking 1 and 2, each consisting of both a lander and an orbiter. The primary objectives were to obtain high-resolution images of the surface, characterize the structure and composition of the atmosphere and surface, and search for evidence of life. The orbiters imaged the entire surface of Mars at a resolution of 150-300 m as well as selected areas at 8 m. The landers transmitted over 1400 images of the two landing sites. The total cost of the Viking project was approximately $1 billion. Viking 1 Mission
The orbiter's primary mission ended on November 5, 1976. Its extended mission began on December 14, 1976, and included a close approach with Phobos in February of 1977. On August 7, 1980, the Viking 1 orbiter was running low on attitude control gas, so its orbit was raised from 357x33,943 km to 320x56,000 km in order to prevent impact with Mars and possible contamination until 2019. The Viking 1 orbiter was powered down on August 17, 1980, after 1485 orbits. The lander, also containing two robot explorers, set down on the western slopes of Chryse Planitia (22.48° N, 49.97° W) on July 20, 1976, at 11:56:06 UT after separating from the orbiter at 08:51 UT. It had spent a few hours at a 300 km altitude before reorienting itself for entry, at which point the aeroshell with an ablatable heat shield slowed the craft as it passed through the atmosphere. During this time, the entry science experiments were conducted. At an altitude of 6 km and speed of 250 m/s, the 16 m diameter parachutes were deployed; 7 seconds later the aeroshell was jettisoned and 8 seconds after that the three lander legs were extended. After 45 seconds the craft had slowed to 60 m/s, and at 1.5 km above the ground retrorockets were fired until the landing 40 seconds later at 2.4 m/s. The rockets used a system that spread the exhaust over a very wide area so that surface heating would be no more than 1 °C and no more than 1 mm of surface material would be removed. After 25 seconds, the first surface image was transmitted. The seismometer failed to uncage, and a sampler arm locking pin was struck and took five days to shake out. Other than these, all experiments functioned normally. It did not find the evidence needed to support life on Mars, but its findings are still being debated by a few people. Viking 1 also sent back color panoramas of Mars, showed that the sky was pinkish due to all of the red dust (rust) in the air, and that there was red soil and red boulders as far as it could see. Also sent back were pictures of canyon systems and what looked like dry river beds. The last data was collected on November 13, 1982, after which a faulty command sent by ground control resulted in loss of contact. After 6.5 unsuccessful months of attempted contact, the mission was officially put to an end on May 21, 1983. The lander was renamed the Thomas Mutch Memorial Station in January 1982 in honor of the leader of the Viking imaging team. Viking 2 Mission
The Viking 2 orbiter developed a leak in its propulsion system that resulted in venting the attitude control gas. It was placed into a 302x33,176 km orbit and was powered down on July 25, 1978, after 706 orbits returning nearly 16,000 images. The lander touched down on Mars on September 3, 1976 at 22:37:50 UT in Utopia Planitia (47.97° N, 225.74° W), following the same ejection and landing procedures described above for Viking 1. However, due to a radar misidentification of a rock or highly reflective surface, the thrusters fired an extra time 0.4 seconds before landing, which cracked the surface and raised dust. The lander settled with one leg on a rock, so it was tilted by 8.2°. The lander's cameras began to take images immediately after landing. It carried out the same mission as the Viking 1, but it also had a working seismometer which recorded one Marsquake, possibly hinting at active plate tectonics (the forces that make mountains, valleys, and the continents move on Earth). The Viking 2 lander ended communications on April 11, 1980, after its batteries failed - it had operated for 1281 Mars days. The lander was renamed the Gerald Soffen Memorial Station. Crafts Orbiters The primary objectives of the Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as a communications relays for the landers, and to perform their own scientific investigations. The orbiter, based on the earlier Mariner9 spacecraft, was an octagon approximately 2.5 m across. The eight faces of the ring-like structure were .4572 m high and were alternately 1.397 and 0.508 m wide. The overall height was 3.29 m from the lander attachment points on the bottom to the launch vehicle attachment points on top. There were 16 modular compartments, three on each of the four long faces and one on each short face. Four solar panel wings extended from the axis of the orbiter, the distance from tip to tip of two oppositely extended solar panels was 9.75 m. The power was provided by eight 1.57x1.23 m solar panels, two on each wing. The solar panels were made up of a total of 34,800 solar cells and produced 620 W of power at Mars. Power was also stored in two NiCd 30 A-hr batteries. The main propulsion unit was mounted above the orbiter bus. Propulsion was furnished by a bipropellant (monomethyl hydrazine and nitrogen tetroxide) liquid-fueled rocket engine which could be gimbaled up to 9 degrees. The engine was capable of 1323 N thrust, translating to a change in velocity of 1480 m/s. Attitude control was achieved by 12 small compressed-nitrogen jets. An acquisition Sun sensor, a cruise Sun sensor, a Canopus star tracker, and an inertial reference unit consisting of 6 gyroscopes allowed three-axis stabilization. Two accelerometers were also on board. Communications were accomplished through a 20-W S-band (2.3 GHz) transmitter and 2 20-W TWTA's. An X-band (8.4 GHz) downlink was also added specifically for radio science and to conduct communications experiments. Uplink was via S-band (2.1 GHz). A 2-axis steerable high-gain parabolic dish antenna with a diameter of approximately 1.5 m was attached at one edge of the orbiter base, and a fixed low-gain antenna extended from the top of the bus. Two tape recorders were each capable of storing 1280 Mbits. A 381 MHz relay radio was also available. Temperature control was achieved by multilayer insulation, thermally activated louvers, and electrical heaters. Scientific instruments for conducting imaging, atmospheric water vapor, and infrared thermal mapping were enclosed in a temperature controlled, pointable scan platform extending from the base of the orbiter. The scientific instrumentation had a total mass of approximately 72 kg. Radio science investigations were also done using the spacecraft transmitter. Command processing was done by two identical and independent data processors, each with a 4096-word memory for storing uplink command sequences and acquired data. Landers Each lander consisted of a 6-sided aluminum base with alternate 1.09 m and 0.56 m long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with 2.21 m sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached to the top of the base, elevated above the surface by the extended legs. Power was provided by two radioisotope thermal generator (RTG) units containing plutonium 238 affixed to opposite sides of the lander base and covered by wind screens. Each generator was 28 cm tall, 58 cm in diameter, had a mass of 13.6 kg and provided 30 W continuous power at 4.4 volts. Four wet-cell sealed nickel-cadmium 8 A-hr, 28 volt rechargeable batteries were also onboard to handle peak power loads. Propulsion was provided for deorbit by a monopropellant hydrazine (N2H4) rocket with 12 nozzles arranged in four clusters of three that provided 32 N thrust, giving a change in velocity of 180 m/s. These nozzles also acted as the control thrusters for translation and rotation of the lander. Terminal descent and landing was achieved by three (one affixed on each long side of the base, separated by 120°) monopropellant hydrazine engines. The engines had 18 nozzles to disperse the exhaust and minimize effects on the ground and were throttleable in the range of 276-2667 N. The hydrazine was purified to prevent contamination of the martian surface. The lander carried 85 kg of propellant at launch, contained in two spherical titanium tanks mounted on opposite sides of the lander beneath the RTG windscreens. Control was achieved through the use of an inertial reference unit, four gyros, an aerodecelerator, a radar altimeter, a terminal descent and landing radar, and the control thrusters. Communications were accomplished through a 20 W S-band transmitter and two 20 W TWTA's. A 2-axis steerable high-gain parabolic antenna was mounted on a boom near one edge of the lander base. An omnidirectional low-gain S-band antenna also extends from the base. Both these antennae allowed for communication directly with the Earth. A UHF (381 MHz) antenna provided a one-way relay to the orbiter using a 30 W relay radio. Data storage was on a 40 Mbit tape recorder, and the lander computer had a 6000-word memory for command instructions. The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the biology, chemical composition (organic and inorganic), meteorology, seismology, magnetic properties, appearance, and physical properties of the martian surface and atmosphere. Two 360° cylindrical scan cameras were mounted near one long side of the base. From the center of this side extended the sampler arm, with a collector head, temperature sensor, and magnet on the end. A meteorology boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A seismometer, magnet and camera test targets, and magnifying mirror are mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the biology experiment and the gas chromatograph mass spectrometer. The X-ray fluorescence spectrometer was also mounted within the structure. A pressure sensor was attached under the lander body. Biology Experiment The biology experiment searched for the presence of Martian organisms by looking for metabolic products. Three distinct instruments (pyrolytic release (PR), labeled release (LR), and gas exchange (GEX)) incubated samples of the Martian surface under several different environmental conditions. In some instances a sample was heat sterilized and reprocessed as a control. The PR, or carbon assimilation, instrument sought to detect the photosynthetic or chemical fixation of CO2 or CO containing C-14. The samples were incubated for several days in the presence of the radioactive gas mixture, some samples with simulated sunlight and some without. Next, each sample was heated to 120 °C to remove unreacted CO2 and CO. The soil was pyrolized at 650 °C and any organic products were collected in an organic vapor trap (OVT). Finally, the trap was heated to combust the organic material to CO2 and any evolved radioactive gas was measured. The LR experiment sought to detect metabolic processes through radiorespirometry. Liquid nutrients labeled with radioactive carbon were added to the samples and the atmosphere above was continuously monitored to detect any radioactive gases released from these nonvolatile nutrients. The GEX measured the production and/or uptake of CO2, N2, CH4, H2, and O2 during incubation of a soil sample. The sample was sealed and purged by He, then a mixture of He, Kr, and CO2 was introduced as an initial incubation atmosphere. After the addition of a selected quantity of a nutrient solution (saturated with the diagnostic gas, neon), the sample was incubated. At certain intervals, samples of the atmosphere were removed and analyzed by a gas chromatograph with a thermal conductivity detector Craft Data
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The
Viking 1 craft was launched from Florida's Cape Canaveral on August 20, 1975.
Its main mission was to study the air, surface, and to search for micro-organisms
in Mars' soil. It reached Mars on June 19, 1976, and spent a month imaging the
surface and looking for good landing sites for its lander and that of Viking
2. The orbit was 1513x33,000 km and took 24.66 hrs to complete.
Viking
2 was launched on September 9, 1975, and it reached Mars on August 7, 1976. It
was placed in a 1500x33,000 km, 24.6 hr orbit that was eventually trimmed to
a periapsis of 1499 km that took 27.3 hrs to complete; it was at an inclination
of 55.2°, and this trimming was completed on August 9. The orbiter's path
took it to several close approaches with Deimos in October of 1977.