Landing platform and small rover on Mars.

NASA's Mars Pathfinder Lander and the Sojourner Rover on Mars.

Was was Pathfinder?

NASA's Mars Pathfinder was designed primarily to demonstrate a low-cost way of delivering a set of science instruments and a free-ranging rover to the surface of the Red Planet.

  • Pathfinder demonstrated a number of innovative, economical, and highly effective approaches to spacecraft and mission design.
  • The wagon-sized Sojourner rover was the forerunner of more advanced rovers such as Spirit, Opportunity and Curiosity.
  • In addition to its engineering accomplishments, Pathfinder provided significant data on Mars' geology and meteorology.

Key Dates

Dec. 4, 1996: Launch

July 4, 1997: Mars landing

July 5 to 25 Sept. 1997: Sojourner rover operated on the surface

Sept. 27, 1997: End of mission


In Depth: Mars Pathfinder

Mars Pathfinder was an ambitious mission to send a lander and a separate remote-controlled rover to the surface of Mars, the second of NASA’s Discovery missions.

Launched one month after Mars Global Surveyor, Pathfinder was sent on a slightly shorter seven-month trajectory designed for arrival earlier. The main spacecraft included a 23-pound (10.5-kilogram) six-wheeled rover known as Sojourner capable of traveling about 545 yards (500 meters) from the main ship at top speeds of a little less than half-inch per second (1 centimeter per second).

The mission’s primary goal was not only to demonstrate innovative, low-cost technologies but also to return geological, soil, magnetic property and atmospheric data. After a seven-month traverse and four trajectory corrections (Jan. 10, Feb. 3, May 6, and June 25, 1997), Pathfinder arrived at Mars on July 4, 1997.

The spacecraft entered the atmosphere using an atmospheric entry aeroshell that slowed it sufficiently for a supersonic parachute to deploy and slow the package to 223 feet per second (68 meters per second).

After separation from the aeroshell heatshield, the lander detached and, at about 1,165 feet (355 meters) above the surface, airbags inflated in less than a second.

Three solid propellant retro-rockets further reduced velocity (firing about 330 feet or 100 meters above the surface), but were then discarded at about 71 feet (21.5 meters) altitude. They flew up and away along with the parachute.

The lander (stowed within the airbag) impacted on the surface at a velocity of about 46 feet per second (14 meters per second) generating about 18 g’s of acceleration. The package bounced at least 15 times before coming to rest, after which the airbags deflated revealing the lander.

Landing time for Pathfinder was 16:56:55 UT July 4, 1997, at 19 degrees 7 minutes 48 seconds north latitude and 33 degrees 13 minutes 12 seconds west longitude in Ares Vallis, about 12 miles (19 kilometers) southwest of the original target.

The next day, Pathfinder deployed the Sojourner rover on the Martian surface via landing ramps. Sojourner was the first wheeled vehicle to be used on any planet. During its 83-day mission, the rover covered hundreds of square miles (meters), returned 550 photographs and performed chemical analyses at 16 different locations near the lander.

Pathfinder transmitted more than 16,500 images and 8.5 million measurements of atmospheric pressure, temperature and wind speed.

Data from the rover suggested that rocks at the landing site resembled terrestrial volcanic types with high silicon content, specifically a rock type known as andesite.

Although the planned lifetimes of Pathfinder and Sojourner were expected to be one month and one week respectively, these times were exceeded by 3 and 12 times respectively.

Final contact with Pathfinder was at 10:23 UT Sept. 27, 1997. Although mission planners tried to re-establish contact for the next five months, the highly successful mission was officially declared over on March 10, 1998.

After landing, Mars Pathfinder was renamed the Sagan Memorial Station after the late astronomer and planetologist Carl Sagan.

In 2003, Sojourner was inducted into the Robot Hall of Fame.

On Dec. 21, 2006, NASA’s Mars Reconnaissance Orbiter’s HIRISE camera photographed the flood plain of the Ares and Tiu outflow channels and the images clearly showed the Pathfinder and associated hardware.

Key Source

Siddiqi, Asif A. Beyond Earth: A Chronicle of Deep Space Exploration, 1958-2016. NASA History Program Office, 2018.

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