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The ''Viking'' program consisted of a pair of identical American
space probe A space probe is an artificial satellite that travels through space to collect scientific data. A space probe may orbit Earth; approach the Moon; travel through interplanetary space; flyby, orbit, or land or fly on other planetary bodies; o ...
s, ''
Viking 1 ''Viking 1'' was the first of two spacecraft, along with '' Viking 2'', each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars la ...
'' and ''
Viking 2 The ''Viking 2'' mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the ''Viking 1'' mission. ''Viking 2'' was operational on Mars for sols ( days; '). The ''Vi ...
'', which landed on
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
in 1976. Each
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, ...
was composed of two main parts: an
orbiter A spacecraft is a vehicle or machine designed to spaceflight, fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth ...
designed to photograph the surface of Mars from
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...
, and a
lander Lander may refer to: Media and entertainment * ''Lander'' (computer game), computer game published by Psygnosis in 1999 * ''Lander'' (game demo), the 3D game demo provided with the Acorn Archimedes computer * Lander (Transformers), a fiction ...
designed to study the planet from the surface. The orbiters also served as communication relays for the landers once they touched down. The Viking program grew from
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
's earlier, even more ambitious,
Voyager Voyager may refer to: Computing and communications * LG Voyager, a mobile phone model manufactured by LG Electronics * NCR Voyager, a computer platform produced by NCR Corporation * Voyager (computer worm), a computer worm affecting Oracle ...
Mars program, which was not related to the successful Voyager deep space probes of the late 1970s. ''Viking 1'' was launched on August 20, 1975, and the second craft, ''Viking 2'', was launched on September 9, 1975, both riding atop
Titan IIIE The Titan IIIE or Titan 3E, also known as the Titan III-Centaur, was an American expendable launch system. Launched seven times between 1974 and 1977, it enabled several high-profile NASA missions, including the Voyager and Viking planetary prob ...
rockets with
Centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as bein ...
upper stages. ''Viking 1'' entered Mars orbit on June 19, 1976, with ''Viking 2'' following on August 7. After orbiting Mars for more than a month and returning images used for landing site selection, the orbiters and landers detached; the landers then entered the Martian
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
and soft-landed at the sites that had been chosen. The ''Viking 1'' lander touched down on the surface of Mars on July 20, 1976, more than two weeks before ''Viking 2''s arrival in orbit. ''Viking 2'' then successfully soft-landed on September 3. The orbiters continued imaging and performing other scientific operations from orbit while the landers deployed instruments on the surface. The project cost was roughly US$1 billion at the time of launch, equivalent to about $ billion in dollars. The mission was considered successful and is credited with helping to form most of the body of knowledge about Mars through the late 1990s and early 2000s.


Science objectives

*Obtain high-resolution images of the Martian surface *Characterize the structure and composition of the atmosphere and surface *Search for evidence of
life on Mars The possibility of life on Mars is a subject of interest in astrobiology due to the planet's proximity and similarities to Earth. To date, no proof of past or present life has been found on Mars. Cumulative evidence suggests that during the ...


Viking orbiters

The primary objectives of the two Viking orbiters were to transport the landers to Mars, perform reconnaissance to locate and certify landing sites, act as communications relays for the landers, and to perform their own scientific investigations. Each orbiter, based on the earlier
Mariner 9 Mariner 9 (Mariner Mars '71 / Mariner-I) was a robotic spacecraft that contributed greatly to the exploration of Mars and was part of the NASA Mariner program. Mariner 9 was launched toward Mars on May 30, 1971 from LC-36B at Cape Canaveral A ...
spacecraft, was an
octagon In geometry, an octagon (from the Greek ὀκτάγωνον ''oktágōnon'', "eight angles") is an eight-sided polygon or 8-gon. A '' regular octagon'' has Schläfli symbol and can also be constructed as a quasiregular truncated square, t, w ...
approximately 2.5 m across. The fully fueled orbiter-lander pair had a
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...
of 3527 kg. After separation and landing, the lander had a mass of about and the orbiter The total launch mass was of which were propellant and
attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...
gas. The eight faces of the ring-like structure were 0.4572 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, 3 on each of the 4 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.


Propulsion

The main
propulsion Propulsion is the generation of force by any combination of pushing or pulling to modify the translational motion of an object, which is typically a rigid body (or an articulated rigid body) but may also concern a fluid. The term is derived f ...
unit was mounted above the orbiter bus. Propulsion was furnished by a
bipropellant The highest specific impulse chemical rockets use liquid propellants (liquid-propellant rockets). They can consist of a single chemical (a monopropellant) or a mix of two chemicals, called bipropellants. Bipropellants can further be divided into ...
(
monomethylhydrazine Monomethylhydrazine (mono-methyl hydrazine, MMH) is a highly toxic, volatile hydrazine derivative with the chemical formula . It is used as a rocket propellant in bipropellant rocket engines because it is hypergolic with various oxidizers such as ...
and
nitrogen tetroxide Dinitrogen tetroxide, commonly referred to as nitrogen tetroxide (NTO), and occasionally (usually among ex-USSR/Russia rocket engineers) as amyl, is the chemical compound N2O4. It is a useful reagent in chemical synthesis. It forms an equilibrium ...
) liquid-fueled
rocket engine A rocket engine uses stored rocket propellants as the reaction mass for forming a high-speed propulsive jet of fluid, usually high-temperature gas. Rocket engines are reaction engines, producing thrust by ejecting mass rearward, in accorda ...
which could be
gimbal A gimbal is a pivoted support that permits rotation of an object about an axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of ...
led up to 9 degrees. The engine was capable of thrust, providing a change in velocity of 1480 m/s.
Attitude control Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...
was achieved by 12 small compressed-nitrogen jets.


Navigation and communication

An acquisition
Sun sensor A sun sensor is a navigational instrument used by spacecraft to detect the position of the sun. Sun sensors are used for attitude control, solar array pointing, gyro updating, and fail-safe recovery. In addition to spacecraft, sun sensors fin ...
, a cruise Sun sensor, a
Canopus Canopus is the brightest star in the southern constellation of Carina and the second-brightest star in the night sky. It is also designated α Carinae, which is Latinised to Alpha Carinae. With a visual apparent magnitude ...
star tracker A star tracker is an optical device that measures the positions of stars using photocells or a camera. As the positions of many stars have been measured by astronomers to a high degree of accuracy, a star tracker on a satellite or spacecraft may ...
and an inertial reference unit consisting of six
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rot ...
s allowed three-axis stabilization. Two
accelerometers An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acce ...
were also on board. Communications were accomplished through a
S-band The S band is a designation by the Institute of Electrical and Electronics Engineers (IEEE) for a part of the microwave radio band, band of the electromagnetic spectrum covering frequency, frequencies from 2 to 4 gigahertz (GHz). Thus it c ...
(2.3
GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
)
transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
and two TWTAs. An
X band The X band is the designation for a band of frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is rather indefinitely set at approxi ...
downlink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...
was also added specifically for radio science and to conduct communications experiments.
Uplink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or sha ...
was via S band A two-axis steerable 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
megabit The megabit is a multiple of the unit bit for digital information. The prefix mega (symbol M) is defined in the International System of Units (SI) as a multiplier of 106 (1 million), and therefore :1 megabit = = = 1000 kilobits. The megabit ...
s. A 381- MHz relay radio was also available.


Power

The power to the two orbiter craft was provided by eight 1.57 × 1.23 m
solar panels A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
, two on each wing. The solar panels comprised a total of 34,800 solar cells and produced 620 W of power at Mars. Power was also stored in two nickel-cadmium 30-
A·h An ampere hour or amp hour (symbol: A⋅h or A h; often simplified as Ah) is a unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing fo ...
batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
. The combined area of the four panels was , and they provided both regulated and unregulated direct current power; unregulated power was provided to the radio transmitter and the lander. Two 30-amp-hour, nickel-cadmium, rechargeable batteries provided power when the spacecraft was not facing the Sun, during launch, while performing correction maneuvers and also during Mars occultation.


Main findings

By discovering many geological forms that are typically formed from large amounts of water, the images from the orbiters caused a revolution in our ideas about
water on Mars Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of ...
. Huge river valleys were found in many areas. They showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and travelled thousands of kilometers. Large areas in the southern hemisphere contained branched stream networks, suggesting that rain once fell. The flanks of some volcanoes are believed to have been exposed to rainfall because they resemble those caused on Hawaiian volcanoes. Many craters look as if the impactor fell into mud. When they were formed, ice in the soil may have melted, turned the ground into mud, then flowed across the surface. Normally, material from an impact goes up, then down. It does not flow across the surface, going around obstacles, as it does on some Martian craters. Regions, called "
Chaotic Terrain In astrogeology, chaos terrain, or chaotic terrain, is a planetary surface area where features such as ridges, cracks, and plains appear jumbled and enmeshed with one another. Chaos terrain is a notable feature of the planets Mars and Mercury, ...
," seemed to have quickly lost great volumes of water, causing large channels to be formed. The amount of water involved was estimated to ten thousand times the flow of the
Mississippi River The Mississippi River is the List of longest rivers of the United States (by main stem), second-longest river and chief river of the second-largest Drainage system (geomorphology), drainage system in North America, second only to the Hudson B ...
. Underground volcanism may have melted frozen ice; the water then flowed away and the ground collapsed to leave chaotic terrain.


Viking landers

Each lander comprised a six-sided aluminium base with alternate long sides, supported on three extended legs attached to the shorter sides. The leg footpads formed the vertices of an equilateral triangle with sides when viewed from above, with the long sides of the base forming a straight line with the two adjoining footpads. Instrumentation was attached inside and on top of the base, elevated above the surface by the extended legs. Each lander was enclosed in an
aeroshell An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry (see blunt body theory). Its main components consist of a heat ...
heat shield designed to slow the lander down during the entry phase. To prevent contamination of Mars by Earth organisms, each lander, upon assembly and enclosure within the aeroshell, was enclosed in a pressurized "bioshield" and then sterilized at a temperature of for 40 hours. For thermal reasons, the cap of the bioshield was jettisoned after the Centaur upper stage powered the Viking orbiter/lander combination out of Earth orbit. Astronomer
Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ex ...
helped to choose landing sites for both ''Viking'' probes.


Entry, Descent and Landing (EDL)

Each lander arrived at Mars attached to the orbiter. The assembly orbited Mars many times before the lander was released and separated from the orbiter for descent to the surface. Descent comprised four distinct phases, starting with a deorbit burn. The lander then experienced
atmospheric entry Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the en ...
with peak heating occurring a few seconds after the start of frictional heating with the Martian atmosphere. At an altitude of about and traveling at a velocity of 900 kilometers per hour (600 mph), the parachute deployed, the aeroshell released and the lander's legs unfolded. At an altitude of about 1.5 kilometers (5,000 feet), the lander activated its three retro-engines and was released from the parachute. The lander then immediately used
retrorockets A retrorocket (short for ''retrograde rocket'') is a rocket engine providing thrust opposing the motion of a vehicle, thereby causing it to decelerate. They have mostly been used in spacecraft, with more limited use in short-runway aircraft land ...
to slow and control its descent, with a
soft landing Soft landing may refer to: *Soft landing (aeronautics) A soft landing is any type of aircraft, rocket or spacecraft landing that does not result in significant damage to or destruction of the vehicle or its payload, as opposed to a hard la ...
on the surface of Mars. At landing (after using rocket propellant) the landers had a mass of about 600 kg.


Propulsion

Propulsion for deorbit was provided by the
monopropellant Monopropellants are propellants consisting of chemicals that release energy through exothermic chemical decomposition. The molecular bond energy of the monopropellant is released usually through use of a catalyst. This can be contrasted with bipro ...
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
(N2H4), through a rocket with 12
nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...
s arranged in four clusters of three that provided thrust, translating to a change in velocity of . These nozzles also acted as the control thrusters for
translation Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...
and
rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
of the lander. Terminal descent (after use of a
parachute A parachute is a device used to slow the motion of an object through an atmosphere by creating drag or, in a ram-air parachute, aerodynamic lift. A major application is to support people, for recreation or as a safety device for aviators, w ...
) and
landing Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown" or ...
utilized three (one affixed on each long side of the base, separated by 120 degrees) monopropellant hydrazine engines. The engines had 1
nozzles
to disperse the exhaust and minimize effects on the ground, and were
throttle A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle' ...
able from . The hydrazine was purified in order to prevent contamination of the Martian surface with Earth
microbes A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
. The lander carried of propellant at launch, contained in two spherical
titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...
tanks mounted on opposite sides of the lander beneath the RTG windscreens, giving a total launch mass of . Control was achieved through the use of an
inertial reference unit An inertial reference unit (IRU) is a type of inertial sensor which uses gyroscopes (electromechanical, ring laser gyro or MEMS) and accelerometers (electromechanical or MEMS) to determine a moving aircraft’s or spacecraft’s change in rotatio ...
, four gyros, a
radar altimeter A radar altimeter (RA), also called a radio altimeter (RALT), electronic altimeter, reflection altimeter, or low-range radio altimeter (LRRA), measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it t ...
, a terminal descent and landing
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...
, and the control thrusters.


Power

Power was provided by two
radioisotope thermoelectric generator A radioisotope thermoelectric generator (RTG, RITEG), sometimes referred to as a radioisotope power system (RPS), is a type of nuclear battery that uses an array of thermocouples to convert the heat released by the decay of a suitable radioa ...
(RTG) units containing
plutonium-238 Plutonium-238 (238Pu or Pu-238) is a fissile, radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter; as alpha particles are easily blocked, this makes the plutonium-238 isotope suit ...
affixed to opposite sides of the lander base and covered by wind screens. Each Viking RTG was tall, in diameter, had a mass of and provided 30 watts continuous power at 4.4 volts. Four
wet cell An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive terminal is the cathode and its nega ...
sealed nickel-cadmium 8 Ah (28,800
coulomb The coulomb (symbol: C) is the unit of electric charge in the International System of Units (SI). In the present version of the SI it is equal to the electric charge delivered by a 1 ampere constant current in 1 second and to elementary char ...
s), 28 volt
rechargeable batteries A rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or prima ...
were also on board to handle peak power loads.


Payload

Communications were accomplished through a 20-watt S-band transmitter using two
traveling-wave tube A traveling-wave tube (TWT, pronounced "twit") or traveling-wave tube amplifier (TWTA, pronounced "tweeta") is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. The TWT belongs t ...
s. A two-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 extended from the base. Both these antennae allowed for communication directly with the Earth, permitting Viking 1 to continue to work long after both orbiters had failed. A
UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (on ...
antenna provided a one-way relay to the orbiter using a 30 watt relay radio. Data storage was on a 40-Mbit tape recorder, and the lander computer had a 6000-
word A word is a basic element of language that carries an objective or practical meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no conse ...
memory for command instructions. The lander carried instruments to achieve the primary scientific objectives of the lander mission: to study the
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
, chemical composition (
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
and
inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemist ...
),
meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
,
seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...
,
magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particl ...
properties, appearance, and physical properties of the Martian surface and atmosphere. Two 360-degree 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 Mechanical temperature sensors * Thermometer * Therm Electrical temperature sensors * Thermistor- Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance wh ...
, and
magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nicke ...
on the end. A
meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did no ...
boom, holding temperature, wind direction, and wind velocity sensors extended out and up from the top of one of the lander legs. A
seismometer A seismometer is an instrument that responds to ground noises and shaking such as caused by earthquakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outpu ...
, magnet and camera test targets, and magnifying
mirror A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
are mounted opposite the cameras, near the high-gain antenna. An interior environmentally controlled compartment held the
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
experiment and the
gas chromatograph Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substan ...
mass spectrometer. The
X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
spectrometer was also mounted within the structure. A
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
sensor was attached under the lander body. The scientific
payload Payload is the object or the entity which is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of ...
had a total mass of approximately .


Biological experiments

The Viking landers conducted biological experiments designed to detect life in the Martian soil (if it existed) with experiments designed by three separate teams, under the direction of chief scientist
Gerald Soffen Gerald A. Soffen (February 7, 1926 – November 22, 2000) was a NASA scientist and educator who served in a wide variety of roles for the space agency, primarily dealing with either education or with life sciences—especially the search for life ...
of NASA. One experiment turned positive for the detection of
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
(current life), but based on the results of the other two experiments that failed to reveal any
organic molecules In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...
in the soil, most scientists became convinced that the positive results were likely caused by non-biological chemical reactions from highly oxidizing soil conditions. Although there was a pronouncement by NASA during the mission saying that the Viking lander results did not demonstrate conclusive
biosignature A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, or molecule – or phenomenon that provides scientific evidence of past or present life. Measurable attribute ...
s in soils at the two landing sites, the test results and their limitations are still under assessment. The validity of the positive 'Labeled Release' (LR) results hinged entirely on the absence of an oxidative agent in the Martian soil, but one was later discovered by the ''Phoenix'' lander in the form of
perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. ...
salts. It has been proposed that organic compounds could have been present in the soil analyzed by both ''Viking 1'' and ''Viking 2'', but remained unnoticed due to the presence of perchlorate, as detected by Phoenix in 2008. Researchers found that perchlorate will destroy organics when heated and will produce
chloromethane Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, odorless, flammable gas. Methyl chloride is a crucial reagent in industrial ...
and
dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible wit ...
, the identical chlorine compounds discovered by both Viking landers when they performed the same tests on Mars. The question of microbial life on Mars remains unresolved. Nonetheless, on April 12, 2012, an international team of scientists reported studies, based on mathematical speculation through complexity analysis of the Labeled Release experiments of the 1976 Viking Mission, that may suggest the detection of "extant microbial life on Mars." In addition, new findings from re-examination of the Gas Chromatograph Mass Spectrometer (GCMS) results were published in 2018.


Camera/imaging system

The leader of the imaging team was Thomas A. Mutch, a geologist at
Brown University Brown University is a private research university in Providence, Rhode Island. Brown is the seventh-oldest institution of higher education in the United States, founded in 1764 as the College in the English Colony of Rhode Island and Providenc ...
in
Providence, Rhode Island Providence is the capital and most populous city of the U.S. state of Rhode Island. One of the oldest cities in New England, it was founded in 1636 by Roger Williams, a Reformed Baptist theologian and religious exile from the Massachusetts ...
. The camera uses a movable mirror to illuminate 12 photo diodes. Each of the 12 silicon diodes are designed to be sensitive to different frequences of light. Several diodes are placed to focus accurately at distances between six and 43 feet away from the lander. The cameras scanned at a rate of five vertical scan lines per second, each composed of 512 pixels. The 300 degree panorama images were composed of 9150 lines. The cameras’ scan was slow enough that in a crew shot taken during development of the imaging system several members show up several times in the shot as they moved themselves as the camera scanned.


Control systems

The Viking landers used a Guidance, Control and Sequencing Computer (GCSC) consisting of two
Honeywell Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...
HDC 402 24-bit computers with 18K of
plated-wire memory Plated-wire memory is a variation of core memory developed by Bell Laboratories in 1957. Its primary advantage was that it could be machine-assembled, which potentially led to lower prices than the almost always hand-assembled core. Instead of t ...
, while the Viking orbiters used a Command Computer Subsystem (CCS) using two custom-designed 18-bit serial processors.


Financial cost of the Viking program

The two orbiters cost US$217 million at the time, which is about $ billion in dollars. The most expensive single part of the program was the lander's life-detection unit, which cost about $60 million then or $ million in dollars. Development of the Viking lander design cost $357 million. This was decades before NASA's "faster, better, cheaper" approach, and Viking needed to pioneer unprecedented technologies under national pressure brought on by the
Cold War The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because t ...
and the aftermath of the
Space Race The Space Race was a 20th-century competition between two Cold War rivals, the United States and the Soviet Union, to achieve superior spaceflight capability. It had its origins in the ballistic missile-based nuclear arms race between the t ...
, all under the prospect of possibly discovering extraterrestrial life for the first time. The experiments had to adhere to a special 1971 directive that mandated that no single failure shall stop the return of more than one experimenta difficult and expensive task for a device with over 40,000 parts. The Viking camera system cost $27.3 million to develop, or about $ million in dollars. When the Imaging system design was completed, it was difficult to find anyone who could manufacture its advanced design. The program managers were later praised for fending off pressure to go with a simpler, less advanced imaging system, especially when the views rolled in. The program did however save some money by cutting out a third lander and reducing the number of experiments on the lander. Overall NASA says that $1 billion in 1970s dollars was spent on the program, which when inflation-adjusted to dollars is about $ billion.As the Viking program was a government expense, the inflation index of the United States
Nominal Gross Domestic Product Gross domestic product (GDP) is a monetary measure of the market value of all the final goods and services produced and sold (not resold) in a specific time period by countries. Due to its complex and subjective nature this measure is ofte ...
per capita is used for the inflation-adjusting calculation.


Mission end

The craft all eventually failed, one by one, as follows: The Viking program ended on May 21, 1983. To prevent an imminent impact with Mars the orbit of ''Viking 1'' orbiter was raised on August 7, 1980, before it was shut down 10 days later. Impact and potential contamination on the planet's surface is possible from 2019 onwards. The ''Viking 1'' lander was found to be about 6 kilometers from its planned landing site by the
Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...
in December 2006.


Message artifact

Each ''Viking'' lander carried a tiny dot of microfilm containing the names of several thousand people who had worked on the mission. Several earlier space probes had carried message artifacts, such as the
Pioneer plaque The Pioneer plaques are a pair of gold-anodized aluminum plaques that were placed on board the 1972 ''Pioneer 10'' and 1973 ''Pioneer 11'' spacecraft, featuring a pictorial message, in case either ''Pioneer 10'' or ''11'' is intercepted by inte ...
and the
Voyager Golden Record The Voyager Golden Records are two phonograph records that were included aboard both Voyager spacecraft launched in 1977. The records contain sounds and images selected to portray the diversity of life and culture on Earth, and are intended for ...
. Later probes also carried memorials or lists of names, such as the ''Perseverance'' rover which recognizes the almost 11 million people who signed up to include their names on the mission.


Viking lander locations


See also

* * * * * *


References


Further reading


On Mars: Exploration of the Red Planet





''Analytical Chemistry'' feature article about the Viking spacecraft's scientific mission

Viking '75 spacecraft design and test summary. Volume 1 Lander design – NASA Report

Viking '75 spacecraft design and test summary. Volume 2 Orbiter design – NASA Report

Viking '75 spacecraft design and test summary. Volume 3 Engineering test summary – NASA Report


External links


NASA Mars Viking Mission

Viking Mission to Mars (NASA SP-334)




Video
A diagram of the Viking and its flight profile

The Viking Mars Missions Education & Preservation Project (VMMEPP)

VMMEPP Online exhibit

45 years ago: ''Viking'' 1 Touches Down on Mars
{{DEFAULTSORT:Viking Program Spacecraft launched in 1975 Missions to Mars NASA programs Astrobiology Derelict landers (spacecraft) 1976 on Mars 1975 in Florida