Mars exploration in the 1990s

The intensive study of Mars by spacecraft

In the 1990’s, NASA began an ambitious, decade-long program to explore Mars by flying two spacecraft to the planet every twenty-six months. This program resulted in high-quality photographic imaging of most of the surface of Mars as well as the deployment of the first rover, a small, semiautonomous laboratory that performed chemical analysis of rocks and soil.

Mars is the most Earth-like planet in the solar system, so it provides insights into how Earth-like planets evolved and, possibly, how life originated. The major objective of the National Aeronautics and Space Administration’s (NASA) Viking 1 and 2 spacecraft, which landed on Mars in 1976, was to search for evidence of life, possibly in the form of microorganisms in the soil. Unfortunately, the reactive chemistry of the Martian soil interfered with these analyses.

After a hiatus of more than fifteen years, NASA resumed its exploration of Mars with the launching of the Mars Observer on September 25, 1992. This large observatory was intended to study the geology and climate. On August 21, 1993, just three days before it was scheduled to enter orbit, radio contact was lost. A review panel determined that a fuel-line rupture in the propulsion system during preparation for orbital insertion probably caused its failure.

Mars Pathfinder

Following the failure of the Mars Observer, NASA shifted its Mars exploration efforts to more frequent but smaller spacecraft. Mars Pathfinder, the second of NASA’s low-cost Discovery missions, was designed to test a new way to deliver payloads to the Martian surface. Pathfinder was launched by a Delta II rocket on December 4, 1996, and landed on Mars on July 4, 1997, directly entering the Martian atmosphere using a small parachute to slow its descent and a system of air bags to cushion its impact. Pathfinder hit the surface at forty miles per hour, bouncing five hundred feet into the air. It bounced sixteen times before coming to rest after 2.5 minutes, about 0.6 mile from its initial impact. The landing site, Ares Vallis, was selected because photographs from the Viking spacecraft indicated it was an ancient floodplain containing a variety of different types of rocks.

The six-hundred-pound Pathfinder carried the twenty-two-pound Sojourner rover, named after the civil rights crusader Sojourner Truth. The six-wheeled rover rolled onto the surface of Mars on July 6. It was controlled from Earth, but the ten-minute time delay for communication required autonomous control of some rover activities. Mars Pathfinder took 16,500 images of the surface and monitored weather. Sojourner took 550 images and analyzed 15 rocks. The results suggest that Mars was once warm and wet with a thick atmosphere. Communications with Pathfinder and Sojourner were lost, for unknown reasons, on September 27, 1997.

Mars Global Surveyor

Launched on November 7, 1996, aboard a Delta II rocket, the Mars Global Surveyor was a fast, low-cost spacecraft to perform most of the science planned for Mars Observer. The spacecraft entered a highly elliptical orbit around Mars on September 12, 1997, and began sixteen months of aerobraking, repeatedly passing through the upper atmosphere to reduce the high point of the orbit, putting it into a nearly circular, two-hour polar orbit. This orbit allowed the Surveyor to observe each spot on Mars every seven days. Beginning in March, 1999, Surveyor performed high-resolution mapping, studied the gravitational field, investigated the role of water and dust on the atmosphere, and mapped the Martian magnetic field. Some images showed bright, new deposits in two gullies, suggesting that water may still flow, at least sporadically, on the Martian surface. High-resolution images of the Cydonia Region showed that the “face on Mars,” a formation resembling a human face in lower-resolution Viking images, was simply a natural rock formation. After studying Mars for four times as long as planned, the Mars Global Surveyor ceased transmitting in November, 2006, probably resulting from a computer error leading to battery failure. The Surveyor was one of the first spacecraft in NASA’s planned, decade-long exploration of Mars, with launches every twenty-six months.

Mars Climate Orbiter and Polar Lander

Launched on December 11, 1998, by a Delta II rocket, the Mars Climate Orbiter carried instruments to study weather, atmospheric ozone, distribution and transport of dust and water, effects of topography on atmospheric circulation, and atmospheric response to solar heating. The spacecraft reached Mars on September 23, 1999, and fired its engine to enter orbit. Radio contact was not reestablished after the spacecraft passed behind Mars. A failure review board determined that some commands were sent in imperial instead of metric units and that the spacecraft was destroyed by atmospheric stresses when it came too close to Mars.

The Mars Polar Lander, launched aboard a Delta II rocket on January 3, 1999, was targeted to land near the edge of the south polar ice cap. The spacecraft was designed to record weather conditions, analyze samples of polar deposits for water and carbon dioxide, and determine soil composition. The last radio signal from the lander was sent just prior to atmospheric entry on December 3, 1999. When the Mars Climate Orbiter was lost, the task of relaying communications from the Polar Lander was shifted to the Mars Global Surveyor, but no communications were received from the surface. The Polar Lander carried two soil penetrators, intended to separate from the spacecraft just before atmospheric entry to measure thermal conductivity of the surface, but these were lost as well.

Impact

Indications that Mars was once warm, wet, and had a dense atmosphere suggest that it was Earth-like in the past, raising the question of how it evolved into an inhospitable planet. The successes of Mars Pathfinder and Mars Global Surveyor set the stage for more ambitious exploration in the twenty-first century, possibly including human exploration of Mars. The Sojourner rover marked the beginning of a program of ever more ambitious Mars rovers in the twenty-first century. However, the failures of the Mars Observer, Mars Climate Orbiter, and Mars Polar Lander emphasized the difficulty of planetary exploration.

Bibliography

Bizony, Piers. The Exploration of Mars: Searching for the Cosmic Origins of Life. London: Aurum Press, 1998. A well-illustrated, two-hundred-page account of the search for life on Mars.

Mishkin, Andrew. Sojourner: An Insider’s View of the Mars Pathfinder Mission. New York: Berkeley, 2004. A firsthand account of the Mars Pathfinder probe by a systems engineer at the Jet Propulsion Laboratory. Illustrated.

Shirley, Donna. Managing Martians. New York: Broadway Books, 1998. An account of the development of Sojourner by the first woman to manage a NASA spaceflight program.