Viking Program

Viking program
Viking I
Type of mission:	Orbiter and Martian landing
Date and time of launch:	20/8/1975 (21:22:00 UTC)
Cohete launcher:	Titan III-E-Centaur
Place of launch:	Cabo Cañaveral (Complege of Launch 41)
Total mass:	3527 kg
Viking II
Type of mission:	Orbiter and Martian landing
Date and time of launch:	9/9/1975 (18:39:00 UTC)
Cohete launcher:	Titan III-E-Centaur
Place of launch:	Cabo Cañaveral (Complege of Launch 41)
Total mass:	3527 kg

NASA's Viking program consisted of two unmanned missions to the planet Mars, known as Viking I and Viking II. This program was to succeed Mariner 9, an orbital probe launched to Mars in 1971 with notable success; The Viking ships would also represent the first two American landing missions on Mars and the first biological study of it. Each mission had an orbital probe (VO or Viking Orbiter) designed to photograph the Martian surface from the planet's orbit, and act as an "intermediary" of communications between the Earth and the Viking landing probe or VL (Viking Lander), which would separate from it and land on the surface of the planet. It was the most expensive and ambitious mission ever sent to Mars to date, with a total cost of approximately $1 billion at the time. It was very successful, and provided most of the information about Mars that was available until then. the late 1990s, with the arrival of the first Martian rovers.

The Viking I was launched on August 20, 1975 and the Viking II on September 9 of the same year, both aboard a Titan III-E rocket.. Once they reached the orbit of Mars, for several months, the orbital probes carried out a reconnaissance of the surface; Once the landing sites were selected, the two sections of the probe were separated, and the landing section entered the atmosphere of Mars, gently landing on the planned location. The orbiters continued to photograph and carry out other scientific operations, while the Viking Lander deployed scientific instruments to the surface. The probe (composed of both parts), fully loaded with fuel, had a mass of 3527 kg.

Orbital Probe: Viking Orbiter

The orbiter was based on the Mariner 9 spacecraft. It was an octagon about 2.5 m in diameter, with a mass, at launch, of about 2,500 kg, of which 1,445 kg was fuel and gas (to control the altitude of the probe once on Mars). The main objectives of the Viking orbiters were:

• The transport of the landing probe (VL-1 and VL-2).
• Photograph the surface of Mars as a map of the planet.
• Conduct a reconnaissance mission to locate and certify possible landing areas.
• Acting as a communications intermediary for the Viking Lander.
• Detect eventual modifications of the Martian environment.

The eight faces of the annular (i.e. ring-shaped) structure had an altitude of 0.4572 m, and had a width of 1397 mm and 508 mm, alternatively. The total height of the probe was 3.29 m. There were 16 modular components, 3 on each of the 4 longest faces, and 1 on each short face.

Orbital mission schedule

Viking Orbiter I

Viking Orbiter II

Orbital propulsion and manoeuvre system

The propulsion unit was placed on the orbiter's power station. The propulsion was achieved through a hypergal fuel rocket engine, which was fueled by a bipropellent system, with monomethylhydrazine (CH)₃N₂H₃) as fuel and dinitrogen tetraoxide (N₂O₄Like oxidizing.

The engine was capable of providing a thrust of 1,323 N, which meant a speed change (Delta-v) of 1,480 m/s. Attitude control was achieved by 12 small compressed nitrogen microthrusters. A solar sensor, a cruise solar sensor, a star navigator and an inertial reference unit with 6 gyroscopes allowed stabilization in 3 dimensions. In addition, the probe had attitude control microthrusters located at the end of the solar panels. Two accelerometers were also on board.

Feeding system

The Viking Orbiter had four "wings" sun rays that extended from the axis of the orbiter. The wingspan of said "wings" It was 9.75 m. The ship obtained energy through 8 solar panels measuring 1.57 m x 1.23 m, placing two on each wing. The solar panels, with a total area of about 15 m², had a total of 34,800 solar cells, which produced 620 W of energy in Martian orbit. The energy was stored in two nickel-cadmium electric batteries with a capacity of 30 Ah (108 kC).

Communications

The communications were achieved with a 20 W transmitter S (2,295 MHz) and two 20 W TWTAs. An X band receiver (8.415 MHz) was placed to perform communications experiments.

The probe had a two-way maneuverable high-gain satellite dish with a diameter of 1.5 m positioned on the edge of the orbiter base. Two tape recorders were capable of storing 1,280 Mbit of information. It also had a 381 MHz UHF radio.

Scientific instruments

The orbital probe carried out three scientific instruments to carry out the planned experiments; an imaging system (Visual Imaging System, VIS), infrared cartography (Infra-Red Thermal Mapper, IRTM), and an atmospheric water vapor detector (Mars Atmospheric Water Derector, MAWD). They were mounted on an orientable platform that was located at the base of the orbiter, so that solar panels never lost the sense of the Sun's rays. The scientific instrument had a total mass of approximately 72 kg:

• VIS or Visual Imaging System (Visual Image System) was composed of two identical cameras, each with a type telescope Cassegrain 755 mm focal distance, a shutter, a tube Vidicon and a portafiltro disc of six sectors. The visual field of each camera was 1.5° x 1.7°, providing images of up to 1.886 km2 for a distance of 1500 km in the perimeter.

• IRTM or Infra-Red Thermal Mapper (Infrared Thermal Folder) was a radiometer with 28 channels that worked in the infrared, consisting of four telescopes with filtering systems and with seven detectors sensitive to a certain spectral field each.

• MAWD or Mars Atmospheric Water Detector (Mars Atmospheric Water Detector) was an infrared spectrometer of five fields of wavelengths located in the region of the water vapor absorption band; this instrument should also measure the proportion of the incident solar radiation in the martian atmosphere, thus determining the amount of water vapor crossed by radiation.

Selection of images obtained by the VIS of the probes Viking Orbiter

Chryse Planitia. Ancient flow of water in the region Maja Valles. "Islas" formed by ancient streams of water in Maja Valles. Martian valleys captured by the probe.

Landing probe: Viking Lander

The Viking Lander I probe, or VL-1, landing section that came together with the Viking Orbiter I orbital probe, was the second space probe to land in Mars successfully, on July 20, 1976 (the first was the Russian Mars 3 spacecraft in 1971, although communication was lost a few seconds after landing on the planet). On September 3, 1976, the Viking Lander II probe, or VL-2, would do the same. The VL-1 and VL-2 probes, once landed on Mars with the instruments deployed, were dedicated to a series of primary objectives:

• Atmospheric studies during descent and landing.
• Observations of the Martian and meteorological environment at the soil level.
• Analysis of soil composition and search for organic matter and life.

Probe structure

The probe consisted of a hexagonal aluminum base supported by three extended legs. The base of the legs formed the vertices of an equilateral triangle with a side of 2.21 m (seen from above). The instruments were attached to the top of the base, and separated from the planet's surface by the extended legs. The entire unit had a mass of 657 kg.

All operations were controlled thanks to the on-board computer, the GCSC or Guidance Control Sequencing Computer. Three units managed the scientific data: the DAPU or Data Acquisition and Processing Unit, which was in charge of collecting scientific and technical data, converting them into numerical data to be later processed. sent to the storage memory or the recorder, or transmitted to the Viking Obiter, so that they could be sent to Earth, or directly sent to the Earth.

Propulsion system and descent maneuver

Propulsion was provided by a monopropellant hydrazine rocket (N₂H₄) with 12 exits arranged in 4 groups of 3, which provided 32 N of thrust, giving a vertical speed of 180 m/s. These exits also acted as control and rotation thrusters for the section of the Viking set to land on Mars.

The final descent and landing on the surface was achieved by three monopropellant hydrazine engines. The engines had 18 outlets to disperse the heat emission and minimize the effects on the surface. They could be regulated, to go from 276 N to 2,667 N. The hydrazine was purified to avoid contaminating the Martian surface. The Viking Lander carried 85 kg of propellant at the time of launch, which was stored in two spherical titanium tanks. Control of the VL was achieved with an interference reference unit, four gyroscopes, an aero-decelerator, a radar altimeter, a descent and landing radar, and the attitude control thrusters.

Feeding system

Power was provided by two radioisotope thermal generators (called RTGs, in English), which contained plutonium 238. Each generator was 28 cm high, 58 cm in diameter and had a mass of 13.6 kg. They generated 35 W continuous, operating at 4.4 volts. It also had 28-volt rechargeable nickel-cadmium batteries, to handle peak supplemental current of 70 W.

Communications

Communication was achieved through a 20 W S-band transmitter, and by means of 2 20 W TWTAs. A parabolic antenna manipulable along two axes was mounted near the edge of the ship's base..

An S-band omnidirectional antenna also extended from the base. Both antennas allowed direct communication with Earth. A 381 MHz UHF antenna allowed one-way communication to the orbiter, using a 30 W radio. Data storage was on a 40 Mbit tape recorder, and the VL computer could store up to 6000 words in orders and procedures.

Scientific instruments

Before the Viking Lander (I and II) landed on the Martian surface, scientific experimentation had already begun. During the descent, the probes observed and measured the Martian atmosphere and ionosphere. During this phase, three instruments worked:

• RPA or Retarding Potential Analyzer (Power Retardizer) measured the distribution of solar wind electrons and ionospheric photoelectrons, electron temperatures in the ionosphere, composition, concentration and temperature of positive ions and the interaction of the solar wind with the high atmosphere.
• UAMS or Upper Atmosphere Mass Spectrometer (High Atmospheric Mass Spectrometer) analyzed the molecular composition of the atmosphere. It provided a quantitative and qualitative analysis of all electrically neutral gases, with a molecular weight less than or equal to an atomic mass of 50. He also measured his isotope abundance.
• LASE or Lower Atmospheric Experiment (Low Atmosphere experiment), which established vertical profiles (density, pressure and temperature) of the atmosphere, from 90 km of altitude to the surface.

Once the Viking Lander landed on Mars, the rest of the onboard instruments were deployed. The 2 cameras provided images of the surface. The photographs (color) were the result of the combination of both cameras by scanning hundreds of lines in blue, red and green. For the physical properties of the soil simple methods were used, such as hardness, analyzed thanks to the sinking of the skids of the probe legs. Two pairs of magnets were placed in the sampling system, separating the magnetic minerals from the rest; Other magnets placed on the metal of the RGTs captured the magnetically charged dust. The Viking Lander was also equipped with three miniature seismometers attached to the lander structure for the measurement of seismic movements.

For meteorological measurements sensors placed at the top of a mast erected after landing were used. Temperatures were measured by means of three thermocouples. An anemometer, also consisting of a thermocouple, was responsible for the speed of the wind and its direction. Likewise, a temperature sensor was located in the sampling system, to establish temperature profiles in the vicinity of the ground. The pressure sensor was placed under the station, and it measured pressure variations as the device descended to the surface.

To collect soil samples, the probes had a sample collection system, consisting of a shovel at the end of a 3-meter-long articulated robotic arm with which to dig. trenches around the probe. The arm crushed the samples and passed them through a sieve, located at the end of it, and then took these samples to the specific compartments for the experiments, under funnels located in the main body of the ship. To analyze the composition of the soil an attempt was made to determine the content of chemical elements and the identification of the molecular composition. The XRFS or X-Ray Fluorescent Spectrometer was in charge of the chemical elements, while the GCSM or Gas Chromatograph Mass Spectrometer Gas Phase) was for molecular analyzes and gas concentrations, organic or inorganic.

Results of the experiments

It was determined that the main neutral constituent of the upper atmosphere is carbon dioxide CO₂; Nitrogen only represents 6% of the amount of CO₂, and molecular oxygen O₂ 0.3%. The presence of nitrogen is very important because this gas is considered a determining factor for the existence of some type of life form.

The weather measures were carried out twelve times a day. They showed average values of daytime temperatures ranging from -85 °C (at sunset) to -29 °C (at noon), daily pressure variations of the order of 0.2 mbar (for an average pressure of 6 mbar), and wind speeds reaching 8 m/s (28.8 km/h) (during the day).

In theory, seismometers should have recorded ground movements, but due to the sensitivity of the stations to the wind, as well as the vibrations of the instruments, the origin of the records was never clearly established.

The soil of Mars is relatively hard, with in some places a crust several centimeters thick that covers a softer level, and some of the surface materials contain magnetic minerals. The XRFS confirmed the presence of iron, calcium, silica, aluminum and titanium in the soil samples collected by the mechanical arm. The GCMS, for molecular and gas analyses, determined that the proportion of argon 36/argon 40 in the Martian atmosphere was much lower than that of the Earth's atmosphere, demonstrating that this planet has not had as important a degassing as the Earth; This instrument did not find sufficient organic complexes (less than one part per million) to affirm any biological process, also presupposing that the water found was associated with certain minerals.

Selection of images of Chryse Planitia obtained by the probe Viking Lander I

First image obtained from the Mars surface of history. Martian panorama where clouds can be seen in the sky. Dunes far away, and ditches dug by the VL-1 for soil samples. Nighting in Mars.

Selection of images of Utopia Planitia obtained by the probe Viking Lander II

Dawn ice cream in Utopia Planitia (the frost is visible on the earth and at the base of the rocks). More ice on Mars. One of the legs of the landing site, some marks of the shovel, and a protective cover of the sample system, ejected (about 20 cm).

Viking biological experiments: the search for life on Mars

One of the main reasons for sending the Martian lander was the recurring search for life on Mars. To do this, the Viking probes that landed on the surface carried with them the Biology Instrument, an experiment container, three exactly; the Pyrolytic Release Experiment, the Labeled Release Experiment, and the Gas Exchange Experiment.

Pyrolytic Release Experiment

This experiment was based on the principle of carbon assimilation, which states that living matter fixes carbon from the atmosphere through photosynthesis. Previously, a part of the sample was sterilized for three hours at 160°C. The samples were incubated for five days under artificial light (without ultraviolet). Then, to return the samples obtained to the natural conditions of the Martian environment, CO₂ labeled with carbon 14 was introduced into the incubation chamber. After the incubation period, the temperature of the container was raised to 650 °C with the aim of pyrolyzing all the organic matter. Helium was then introduced to transfer the vapor phase through a filter, and the rest of the volatile groups were analyzed using a radiation detector, so that the carbon 14 that could have been fixed by the organic matter could be detected. The sterilized and non-sterilized samples were compared to measure radioactivity. If the results were the same, it was assumed that there was no biological agent; If it was different, the presence of organic matter that would have altered the result could be admitted.

Labeled Release Experiment

The Labeled Release Experiment was based on the concept of the assimilation of organic molecules, such as amino acids, by microorganisms present in soil samples; After assimilation, a series of gases would be produced that contained a part of the carbon present in the organic molecules. To do this, the samples were placed in an incubator with a Martian atmosphere. A liquid nutritional agent (with formates, lactates and amino acids) labeled at carbon 14 would be added to said sample. If during the experiment there was an increase in the radioactivity of the atmosphere of the incubator, it had to be thought that it was the result of the emission of gases labeled carbon 14 produced by the assimilation of nutritional matter by Martian microorganisms.

Gas Exchange Experiment

This other experiment was based on the principle of exchanges between living matter and the atmosphere, and on the presence of nutritious matter in the soil. The sample was added, inside the incubator, an unlabeled nutrient agent and a gas mixture of helium, krypton and carbon dioxide. In the experiment, the samples of the gas mixture were analyzed in a chromatrographic column, so that an eventual increase in the concentration of carbon dioxide, CH₄, and nitrogen could be detected, which would indicate a assimilation of nutritive matter by living matter.

Analysis of biological experiments

After analyzing the results of biological experiments, the scientific community was reserved to qualify that some biological process existed on the surface of Mars. Three experiments were performed; in the first one a sample of 0.1 g of the soil collected by the mechanical arm was used by introducing it into the incubator. This experiment was the Pyrolytic Release Experiment. After conducting the experiment, in which martian conditions without ultraviolet rays were simulated, the presence of biological agents would be affirmed by detecting the photosynthesis of possible microorganisms. The analyzer detected the presence of gaseous emanations of carbonaceous compounds that in principle were carbon dioxide and, in a sterilized twin sample, no such circumstance was given. Therefore the result was positive for the presence of living beings.

In the second experiment, which was the Labeled Release Experiment, an organic broth was used for the sample so that the possible microorganisms existing in said sample would emit carbon dioxide due to the metabolism of this compound. This result was initially negative, since it did not provide any valid results in the heated sample.

In the last experiment, the Gas Exchange Experiment sought to look for organic metabolites, such as methane, after contributing to the sample organic nutrients marked to carbon 14. The result was probably positive, since a variation in nitrogen was found after observing the sample for 200 days, apart from an obvious detachment of oxygen and carbon dioxide.

The scientists then determined, not with total conviction, that the presence of life in Mars was nonexistent. They were based on the positive results of the first and third experiment, which could be explained through chemical and geological processes. In the case of the second experiment, which was negative, scientists argued that perhaps the analyzer was too little sensitive to detect organic traces in so little amount.

Finally they explained that perhaps the best way to find biological agents in Mars would be to dig a certain depth of the soil, as the lethal ultraviolet rays would destroy any kind of life (the ozone layer does not exist in Mars).

Much more recently, it has been argued that Viking probes could not only be incapable of detecting life in Mars and, above all, that scientists might not have been able to interpret the data they transmitted, but because of the multiple experiments the probes could have ended with the life existing in the samples, since the possible Martian microorganisms would not respond just as the terrestrials to the chemical processes to which they would have been exposed.