Washington - Thirty years after the first landing on Mars by NASA's Viking spacecraft, the ambitious mission continues to spark enthusiasm for future space exploration.

NASA's Viking 1 and Viking 2 missions to Mars, each consisting of an orbiter and a lander, became the first space probes to obtain high resolution images of the Martian surface, characterize the structure and composition of the atmosphere and surface, and conduct on-the-spot biological tests for life on another planet.

Viking 1 launched August 20, 1975, and arrived at Mars June 19, 1976, according to a July 14 NASA press release.

On July 20, 1976, the Viking 1 lander separated from the orbiter and touched down in a Martian plain called Chryse Planitia. Viking 2 launched September 9, 1975, and entered Mars orbit August 7, 1976. The Viking 2 lander touched down in Utopia Planitia September 3, 1976.

"The Viking team didn't know the Martian atmosphere very well; we had almost no idea about the terrain or the rocks, and yet we had the temerity to try to soft land on the surface," recalled Gentry Lee, solar system exploration chief engineer at NASA's Jet Propulsion Laboratory in California.

"We were both terrified and exhilarated," he added. "All of us exploded with joy and pride when we saw that we had indeed landed safely."

Originally designed to function for 90 days, the Viking spacecraft continued collecting data for more than six years. The landers accumulated 4,500 close-up images of the Martian surface.

The accompanying orbiters provided more than 50,000 images, mapping 97 percent of the planet. NASA scientists still are analyzing and interpreting the orbiters' and landers' measurements of the Mars atmosphere and surface. The data provided by Viking suggested that early Mars was very different from the present-day planet.

Viking performed the first successful Mars entry, descent and landing. Derivations of a Viking-style thermal protection system and parachute have been used on every U.S. Mars lander mission, including Mars Pathfinder (1996-1998) - an engineering demonstration of key technologies and concepts for future Mars missions - and the Mars rovers (2004-present), Spirit and Opportunity.

Additional information and a press release on the 30th anniversary on the Viking mission are available at the NASA Web site.

For ongoing coverage of the U.S. space program, see Science and Technology.