Our Spaceflight Heritage: Invasion of the Vikings
Forty years ago, NASA’s Viking landers roared to a hover over the Martian surface and touched down. They were the culmination of the ambitious Mars Voyager (no relation to NASA’s Voyager probes) program that had begun near the end of the Apollo era and filed down to a more manageable size due to budget cuts. Despite the reduced scope, the Viking program was a tremendous success.
Viking gave NASA the most knowledge the agency had about Mars until the 1990s and 2000s, when Pathfinder, Phoenix, Mars Exploration Rovers, and the Mars Science Laboratory rover Curiosity arrived.
Both spacecraft were identical, for redundancy, in case one of them failed prematurely. Given that NASA’s engineering teams had no experience with Martian conditions, that was a considered to be a prudent design decision. It ensured the return of twice the scientific and engineering data to Earth than what would have been possible with a single spacecraft – from two different locations on the surface of the Red Planet.
“We were science driven, rather than aeronautics, rather than space, rather than technology. We never lost sight of what our customer was,” Gus Guastaferro, Viking’s deputy project manager said. “Our customer was knowledge and science.”
Viking 1 was launched on August 20, 1975, with Viking 2 roaring aloft on Sept. 9, both on Titan-III rockets with Centaur upper stages. Viking 1 arrived into Mars orbit on June 19, 1976, after a transit time of ten months. Viking 2 followed suit on August 7.
After a month orbiting Mars and transmitting photos of potential landing sites back to Earth, the Viking 1 lander split from its orbiter and descended toward Chryse Planitia (literally, “golden plain”) near the equator. Viking 2 landed at Utopia Planitia (“plain of nowhere”) further north and on the opposite side of the planet. Both sites were relatively low and flat.
Viking’s controllers did not want to risk landing in rough or high terrain, which would have made atmospheric deceleration and hazard avoidance more difficult. The wide expanse of these sites – unbounded by rough terrain for many kilometers in all directions – added a safety factor to the landings.
The Viking lander measured 10 feet (3 meters) across and 6.5 feet (2 meters) tall when fully deployed. Its core was a six-sided titanium and aluminum box with three landing legs, each leg attached to one of the box’s short sides. It was powered by a pair of radioisotope thermoelectric generators (RTGs) on either side.
Also attached to the lander were a pair of cameras, an extendable sampling arm, and a deployable meteorology arm with mounted sensors to measure temperature, wind direction, and wind speed.
Scientific instruments on the landers included a seismometer, a gas chromatograph / mass spectrometer (GCMS), an X-ray fluorescence spectrometer, and a biology package. The latter consisted of a pyrolytic-release experiment, a carbon assimilation experiment, and a labeled-release experiment, designed to find evidence of microscopic life in Martian regolith. Each experiment was designed by a separate team, and they were tested multiple times on different regolith samples.
The Viking landers used three clusters of retro-rockets with 18 nozzles each in order to distribute the exhaust across the surface and prevent overheating of the top layer of regolith at the landing site.
Because of concern about Earthly microorganisms sticking to the spacecraft on their way to Mars, the lander and aeroshell were carefully sterilized and encased in an egg-shaped pressurized bio-barrier 6 feet (1.9 meters) high. Any Earth organism that survived sterilization carried a risk of throwing off the biological readings, so the sterilization program was carried out as thoroughly as possible. Each lander was baked for hours at high temperatures and carefully wiped down with disinfectants and ultra pure water.
The landers transmitted over 1,400 images from both sites. Soil analysis at both sites found the Martian regolith to resemble iron-rich clay, similar to these produced from the weathering of basaltic lava. Magnets on the sampling arms found the regolith to consist of 3–7 percent magnetic minerals.
The three biology experiments, in addition to the GCMS, all returned negative except for the Labeled-Release experiment. That experiment used radioactive carbon-14 (14C), which was injected into a sample of Martian regolith. The air above the soil was monitored for 14CO2 – which implied metabolic activity. In both landers, there was a steady stream of radioactive gases being coming out of the soil sample at the first injection. Subsequent injections a week later did not return the same reaction, and the result remains inconclusive.
The GCMS found chloromethane and dichloromethane in amounts of parts-per-billion. They were thought to be residues of the spacecraft’s cleaning process, but Phoenix’s discovery of perchlorates led to a reinterpretation of the results. Perchlorates are strong oxidizers when heated to 200 °C, and their reaction with organic molecules could have generated the chlorine compounds that the Viking landers found.
Meanwhile, the orbiter bus was an octagon 8 feet (2.5 meters) in diameter and 1.5 feet (0.4572 meters) high. From the bus extended four solar wings, capable of providing 620 watts of total power at Mars. Power storage was accomplished with 2 nickel-cadmium batteries of 30-amp-hour each. The main propulsion unit was mounted above the orbiter bus, consisting of a liquid bipropellant rocket engine that could be gimballed up to 9 degrees in any direction.
That engine ran on monomethyl hydrazine (MMH) fuel and nitrogen tetroxide (NTO) oxidizer. Attitude control was provided by twelve small compressed-nitrogen jets. The lander inside its aeroshell was attached to the opposite side of the bus from the main engine.
A scientific instrument suite was enclosed in a temperature-controlled, pointable scan platform extending from the base of the orbiter. That suite included a pair of television cameras, a thermal mapper (infrared radiometers), and an atmospheric water sensor (infrared spectrometer). Radio science investigations were done using the orbiter’s transmitter.
The Viking orbiters returned the first detailed color images of Mars, covering the entire planet, with a resolution of 150 to 300 meters. Selected areas were imaged at 8-meter resolution. This led to the discovery of Mars’ bimodal geography, in which most of the smoother northern hemisphere is several kilometers lower than the cratered southern hemisphere.
In addition, the orbiters detected multiple pieces of evidence for bodies of water on the Martian surface in the past, such as ancient river valleys, teardrop-shaped islands, and deep grooves carved into bedrock.
The Viking missions returned a wealth of scientific and engineering data on the Martian environment, which made the Pathfinder and Mars Exploration Rover missions possible. The ambiguity of the Viking biological results might be resolved by the Curiosity rover at some point in the future.
While the march of Martian exploration missions continues with ever-increasingly sophisticated robotic geologists, the Viking landers will forever be remembered as the first spacecraft to touch down on the dusty plains of Mars and operate for an extended period of time.
Perhaps of greater importance is that, one day, the ‘inconclusive’ data might be validated and life on Mars could become a proven reality. If so, the Viking landers may have made one of the most important discoveries in human history.
“In addition to the 5,500 pictures of Mars’ surface, in addition to the first measurements of the atmosphere composition, pressure and density, in addition to the discovery that the surface of Mars is unlike any other surface in the Solar System, it just may be that in 1976 the people sitting in this room discovered the presence of life on Mars,” Joel Levine, a former NASA Langley scientist said.
Eric Shear is a recent graduate from York University, honors bachelor in space science. Before that, Shear studied mechanical engineering at Tacoma Community College. During this time, Shear helped develop the HYDROS water-electrolysis propulsion system at Tethers Unlimited and led a microgravity experiment on the Weightless Wonder parabolic aircraft. Shear has worked for an extended period of time to both enable and promote space flight awareness. Shear agreed to contribute to SpaceFlight Insider’s efforts so that he could provide extra insight into interplanetary missions, both past and present.