NASAs Viking Project

The Viking Project was the culmination of an initial series of U.S. missions to explore Mars in the 1960s and 1970s. This series of interplanetary missions began in 1964 with Mariner 4, continued with the Mariner 6 and 7 flyby missions in 1969, and ended to date with the Mariner 9 orbital mission in 1971 and 1972. Viking robot spacecraft were designed as a complement pair: one to orbit Mars and one to land and operate on the surface of the Red Planet. Reflecting the aerospace engineering philosophy of redundant missions that were characteristic of the 1970s, NASA constructed and launched two identical missions, each consisting of a lander and an orbiter. In many respects, the Viking spacecraft represented the most sophisticated attempt by humans in the 20th century to find life on Mars using robot spacecraft. Chapter 4 discusses contemporary attempts

S-band low-gain antenna

Canopus tracker Stray light sensor Orbiter bus Solar panel

Orbiter propulsion mntnr

Oxidizer tank Relay antenna

S-band low-gain antenna

Orbiter propulsion mntnr

Oxidizer tank Relay antenna

Exo Microbiology Viking Experiment

Mars atmospheric water detector

Infrared thermal mapper Attitude control Visual imaging cameras gas jets

Mars atmospheric water detector

Infrared thermal mapper Attitude control Visual imaging cameras gas jets

NASA's Viking orbiter spacecraft and its complement of instruments. (NASA)

to look for life on Mars with robot spacecraft, many of which build upon the Viking Project's technical legacy.

The Viking Project orbiters carried the following scientific instruments:

1. A pair of cameras with 1,500-millimeter focal length that performed systematic searches for landing sites, then looked at and mapped almost 100 percent of the Martian surface. Cameras onboard the Viking 1 and Viking 2 orbiters took more than 51,000 photographs of Mars.

2. A Mars atmospheric water detector that mapped the Martian atmosphere for water vapor and tracked seasonal changes in the amount of water vapor.

3. An infrared thermal mapper that measured the temperatures of the surface, polar caps, and clouds; it also mapped seasonal changes. In addition, although the Viking orbiter radios were not considered scientific instruments, they were used as such. By measuring the distortion of radio signals as these signals traveled from the Viking orbiter spacecraft to Earth, scientists were also able to measure the density of the Martian atmosphere. The ground-based, large radio telescopes of NASA's Deep Space Network (DSN) played a critical role in these efforts.

The Viking Project landers carried the following instruments:

1. The biology instrument, consisting of three separate experiments that were designed to detect evidence of microbial life in the

NASA's Viking lander spacecraft and its complement of instruments. (NASA)

Magnifying mirror

Radar altimeter electronics no. 2

Magnet and camera test target

Seismometer

UHf antenna (relay) RTC power sources (2)

S-band low-gain antenna

Roll engines (4)

Terminal descent propellant tanks (2)

Radar altimeter antenna and terminal descent landing radar(underside ofTander structure)

X-ray fluorescence funnel

S-band high-gain antenna (direct)

Gems processor

Cameras (2)

Meteorology

Landing shock absorber Magnet cleaning brush

Biology processor

Surface sampler boom

Collector head

S-band high-gain antenna (direct)

Gems processor

Cameras (2)

Meteorology

Landing shock absorber Magnet cleaning brush

Biology processor

Surface sampler boom

Collector head

Martian soil. There was always a remote chance that larger life-forms could be present on Mars. But NASA's exobiologists thought then (as they do now) that any native life-forms currently existing on Mars would most likely be microorganisms.

2. A gas chromatograph/mass spectrometer (GCMS) that searched the Martian soil for complex organic molecules. Any such complex organic molecules could be the precursors or the remains of living organisms.

3. An X-ray fluorescence spectrometer that analyzed samples of the Martian soil to determine its elemental composition.

4. A meteorology instrument that measured air temperature and wind speed and direction at the landing sites. These instruments returned the first extraterrestrial weather reports in the history of meteorology.

5. A pair of slow-scan cameras that were mounted about 3-feet (1-m) apart on the top of each lander spacecraft. These cameras provided black-and-white, color, and stereo photographs of the Martian surface.

6. A seismometer that was designed to record any "Marsquakes" that might occur on the Red Planet. Such information would have helped planetary scientists determine the nature of the planet's internal structure. Unfortunately, the seismometer on the Viking 1 lander did not function after landing, and the instrument on the Viking 2 lander observed no clear signs of internal (tectonic) activity on the planet.

7. An upper-atmosphere mass spectrometer that conducted its primary measurements as each robot lander plunged through the Martian atmosphere on its way to the landing site. This instrument made the Viking 1 lander's first important scientific discovery, the presence of nitrogen in the Martian atmosphere.

8. A retarding potential analyzer that measured the Martian ionosphere, again during entry operations.

9. Accelerometers, a stagnation pressure instrument, and a recovery temperature instrument that helped determine the structure of the lower Martian atmosphere as each of the lander spacecraft approached the surface of the planet.

10. A surface sampler boom that employed its collector head to scoop up small quantities of Martian soil to feed the biology, organic-chemistry, and inorganic-chemistry instruments. It also provided clues to the soil's physical properties. Magnets attached to the sampler, for example, provided information on the soil's iron content.

11. In addition to sending scientific data back to scientists on Earth via NASA's Deep Space Network, the lander spacecraft radios also were used to conduct scientific experiments. Physicists were able to refine their estimates of Mars's orbit by measuring the time for radio signals to travel between Mars and Earth. The great accuracy of these radio-wave measurements also allowed scientists to confirm portions of Albert Einstein's general theory of relativity.

Both Viking missions were launched from Cape Canaveral, Florida. Viking 1 was launched on August 20, 1975, and Viking 2 on September 9, 1975. The landers were carefully sterilized before launch to prevent contamination of Mars by terrestrial microorganisms. These spacecraft spent nearly a year in transit to the Red Planet. Viking 1 achieved Mars orbit on June 19, 1976, and Viking 2 began to orbit Mars on August 7, 1976. The Viking 1 lander spacecraft accomplished the first soft landing on Mars on July 20, 1976, on the western slope of Chryse Planitia (the Plains of Gold) at 22.46° north latitude, 48.01° west longitude. The Viking 2 lander touched down successfully on September 3, 1976, at Utopia Planitia (the Plains of Utopia) at 47.96° north latitude, 225.77° west longitude.

The Mars surface science portion of the Viking mission was originally planned to be conducted for approximately 90 days after landing. However, each orbiter and lander pair successfully operated far beyond their design lifetimes. For example, the Viking 1 orbiter exceeded four years of active flight operations in orbit around Mars. The Viking Project's primary mission ended on November 15, 1976, just 11 days

NAsA's Approach to Reducing the Bioload of the Viking Landers

NASA engineers and scientists used a twofold approach to control the population of "hitchhiking" terrestrial microorganisms that could find their way to the surface of Mars— thereby causing forward contamination of the Red Planet. The first step involved a very careful presterilization cleaning of the lander spacecraft during assembly; the second step involved postassembly heat sterilization.

Engineers and technicians carefully assembled the Viking 1 and 2 lander spacecraft in Class 100,000 clean rooms. During assembly operations, the technical team conducted thousands of microbial assays. These assays established that the average spore burden was less than 28 per square foot (300 per square meter) and that the total burden of spores on the lander spacecraft's surface was less than 300,000. In performing the microbiological assays, NASA personnel used the spore-forming microbe Bacillus subtilis as the indicator organism because of this microbe's enhanced resistance to heat, radiation, and desiccation.

After the Viking 1 and 2 landers had been assembled and sealed inside their respective bioshields, the bioload of each lander spacecraft was further reduced by dry heating. Aerospace workers heated the landers to a minimum temperature of 233°F (111.7°C) for about 30 hours. NASA exobiologists estimated that the bioburden of each lander spacecraft was reduced by a factor of 104 as a result of this thermal sterilization procedure.

before Mars passed behind the Sun (an astronomical event called a superior conjunction). After conjunction, in mid-December 1976, telemetry and command operations were reestablished, and extended mission operations began.

The Viking 2 orbiter mission ended on July 25, 1978, due to exhaustion of attitude-control system gas. The Viking 1 orbiter spacecraft also began to run low on attitude-control system gas, but through careful planning, it was possible to continue collecting scientific data (at a reduced level) for another two years. Finally, with its control gas supply exhausted, the Viking 1 orbiter's electrical power was commanded off on August 7, 1980.

The last data from the Viking2 lander were received on April 11, 1980. The Viking 1 lander made its final transmission to Earth on November 11, 1982. After more than six months of futile efforts to regain contact with the Viking 1 lander, NASA mission controllers ended Viking mission operations on May 23, 1983.

With the single exception of the seismic instruments, the entire complement of scientific instruments carried off the Viking Project spacecraft acquired far more data about Mars than ever anticipated. The seismometer on the Viking 1 lander did not function after touchdown, while the seismometer on the Viking 2 lander detected only one event that might have been of seismic origin. Nevertheless, the instrument still provided data on surface wind velocity at the Utopia Planitia site (supplementing the meteorology experiment) and also indicated that the Red Planet currently has a very low level of seismicity.

The primary objective of the robot landers was to determine whether life currently exists on Mars. Three of the lander's instruments were capable of detecting microbial life on Mars. In addition, the lander cameras could have photographed any living creatures large enough to be seen with the human eye. These cameras would also have observed growth in organisms such as plants and lichens. Unfortunately, the cameras at both landing sites observed nothing that could be interpreted as living. Although the evidence provided by the Viking 1 and 2 landers concerning the presence of microbial life is still subject to some debate, today most scientists regard the null results as strongly indicative of the fact that life does not currently exist on Mars—at least at either landing site.

The gas chromatograph/mass spectrometer (GCMS) could have found organic molecules in the soil. (Organic compounds combine carbon, nitrogen, hydrogen, and oxygen.) These compounds are present in all living matter on Earth. The GCMS was programmed to search for heavy organic molecules, those large molecules that contain complex combinations of carbon and hydrogen and are either life precursors or the remains of living systems. To the surprise of exobiologists, the GCMS (which easily detected organic matter in the most barren soils found on Earth) found no trace of any organic molecules in the Martian soil samples scooped up and tested at each landing site.

The biology instrument on each lander spacecraft was the primary device used to search for extraterrestrial life. It was a 1-cubic-foot (0.0286-cubic-meter) box, loaded with the most sophisticated scientific instrumentation yet built and flown in space. The biology instrument actually contained three smaller instruments that examined the Martian soil for evidence of metabolic processes like those used by bacteria, green plants, and animals here on Earth.

The three biology experiments worked flawlessly on each Viking lander. All showed unusual activity in the Martian soil—activity that mimicked life—but exobiologists here on Earth needed time to understand the strange behavior of the Red Planet's soil. Today, according to most scientists who helped analyze these data, it appears that the chemical reactions were not caused by living things.

Furthermore, the immediate release of oxygen, when the Martian soil contacted water vapor in the biology instrument, and the lack of organic compounds in the soil indicated that oxidants were present in both the

Martian soil and the atmosphere. Oxidants, such as peroxides and superoxides, are oxygen-bearing compounds that break down organic matter and living tissue. Consequently, even if organic compounds evolved on Mars, they would have been quickly destroyed.

Evaluation of the Martian atmosphere and soil has revealed that all the elements essential for life (as known on Earth)—carbon, hydrogen, nitrogen, oxygen, and phosphorus—are also present on the Red Planet. However, exobiologists currently consider the presence of liquid water on a planet's surface as an absolute requirement for the evolution and continued existence of life. The Viking Project discovered ample evidence of Martian water in two of its three phases, namely vapor and solid (ice), and even evidence of large quantities of permafrost. But under current environmental conditions on Mars, it is impossible for water to exist as a liquid on the planet's surface.

Viking spacecraft data indicated that the conditions now occurring on and just below the surface of the Red Planet do not appear adequate for the existence of living (carbon-based) organisms. However, exobiologists, though disappointed in their first serious search for extraterrestrial life, recognize that the case for life sometime in the past history of Mars is still open. Some scientists even cautiously speculate that viable microbial life-forms might still be found in selective, subsurface enclaves where small quantities of liquid water may possibly occur. The search for such ecological niches is one of the major objectives of the numerous NASA robotic missions to Mars in the first decade of this century. (Chapter 4 discusses some of these efforts.)

While the gas chromatograph/mass spectrometer found no sign of organic chemistry at either landing site, the instrument did provide a precise and definitive analysis of the composition of the Martian atmosphere. For example, the GCMS found previously undetected trace elements. The lander spacecraft's X-ray fluorescence spectrometer measured the elemental composition of the Martian soil.

In addition to conducting an automated search for life, the two robot landers continuously monitored weather at the landing sites. The midsummer Martian weather proved repetitious, but in other seasons, the weather varied and became more interesting. Cyclic variations in Martian weather patterns were observed. Atmospheric temperatures at the southern (Viking 1) landing site were as high as 6.8°F (-14°C) at midday, while the predawn summer temperature was typically -107°F (-77°C). In contrast, the diurnal temperatures at the northern (Viking2) landing site during the midwinter dust storm varied as little as 39°F (4°C) on some days. The lowest observed predawn temperature was -184°F (-120°C), which is about the frost point of carbon dioxide. A thin layer of water frost covered the ground near the Viking 2 lander each Martian winter.

The barometric pressure was observed to vary at each landing site on a semiannual basis. This occurred because carbon dioxide (the major constituent of the Martian atmosphere) freezes to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of "snow" and then evaporates (or sublimes) again with the advent of Martian spring in each hemisphere. When the southern cap was largest, the mean daily pressure observed by Viking 1 lander was as low as 6.8 millibars (680 Pa), while at other times during the Martian year, it was as high as 9.0 millibars (900 Pa). Similarly, the pressures at the Viking 2 lander site were 7.3 millibars (730 Pa) (full northern cap) and 10.8 millibars (1,080 Pa). For comparison, the sea-level atmospheric pressure on Earth is about 1,000 millibars (101,300 Pa).

Martian surface winds were also generally slower than anticipated. Scientists had expected these winds to reach speeds of a few hundred miles (km) per hour. But neither Viking lander recorded a wind gust in excess of 75 miles per hour (120 km/h), and average speeds were considerably lower.

Photographs of Mars from the Viking landers and orbiters surpassed all expectations in both quantity and quality. Together, the Viking 1 and 2 landers provided more than 4,500 images, and the Viking 1 and 2 orbiters more than 51,000. The landers provided the first close-up view of the surface of the Red Planet, while the orbiters mapped almost 100 percent of the Martian surface, including detailed images of many intriguing surface features.

The infrared thermal mapper and the atmospheric water detector onboard the Viking 1 and 2 orbiters provided essentially daily data. Through these data, it was determined that the residual northern polar ice cap that survives the northern summer is composed of water ice, rather than frozen carbon dioxide (dry ice), as scientists once believed.

Today, after all the Viking Project robot explorers have fallen silent, their data represents a valuable technical heritage that supports the current wave of investigation of Mars with even more sophisticated robot spacecraft. Following in the footsteps of the highly successful Viking spacecraft, new generations of robot explorers now scan and scamper across the surface of the Red Planet hoping to answer the intriguing questions about Mars that still remain, especially in the fields of exobiology and comparative planetology. Is there a remote possibility that life exists in some crevice or biological niche on this mysterious world? Did life once evolve there, only to have vanished millions of years ago? And how did climatic conditions change so radically that great floods of water, which apparently raged over the Martian plains, have now vanished, leaving behind the dry, sterile world found by the Viking Project explorers? Only further exploration during this century, including possibly human expeditions, can solve these intriguing mysteries.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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