The History of the Mars Pathfinder Mission

Mars Pathfinder Mission
Mars Pathfinder Mission. NASA

Meet Mars Pathfinder

The Mars Pathfinder was the second of NASA's low-cost planetary Discovery missions to be launched. It was an ambitious way to send a lander and a separate, remote-controlled rover to the surface of Mars and demonstrated a number of innovative, economical, and highly effective approaches to spacecraft and mission design of a planetary landing mission. One reason it was sent was to show the feasibility of low-cost landings at Mars and eventual robotic exploration.


Mars Pathfinder was launched on a Delta 7925 on December 4, 1996. The spacecraft entered the Martian atmosphere on July 4, 1997 and took atmospheric measurements as it descended. The entry vehicle's heat shield slowed the craft to 400 meters per second in about 160 seconds.

A 12.5-meter parachute was deployed at this time, slowing the craft to about 70 meters per second. The heat shield was released 20 seconds after parachute deployment, and the bridle, a 20-meter-long braided Kevlar tether, deployed below the spacecraft. The lander separated from the back shell and slid down to the bottom of the bridle over about 25 seconds. At an altitude of about 1.6 kilometers, the radar altimeter acquired the ground, and about 10 seconds before landing four air bags inflated in about 0.3 seconds forming a 5.2-meter-wide diameter protective 'ball' around the lander.

Four seconds later at an altitude of 98 meters the three solid rockets, mounted in the backshell, fired to slow the descent, and the bridle was cut 21.5 meters above the ground.

That released the airbag-encased lander, which dropped to the ground. It bounced about 12 meters into the air, bouncing at least another 15 times and rolling before coming to rest approximately 2.5 minutes after impact and about a kilometer from the initial impact site.

After landing, the airbags deflated and were retracted.

Pathfinder opened its three metallic triangular solar panels (petals) 87 minutes after landing. The lander first transmitted the engineering and atmospheric science data collected during entry and landing. The imaging system obtained views of the rover and immediate surroundings and a panoramic view of the landing area. Eventually, the lander's ramps were deployed and the rover rolled onto the surface. 

The Sojourner Rover

The Pathfinder's rover Sojourner was named in honor of Sojourner Truth, a 19th-century abolitionist and champion of women's rights. It operated for 84 days, 12 times longer than its designed lifetime of seven days. It investigated rocks and soil in the area around the lander. 

The bulk of the lander's task was to support the rover by imaging rover operations and relaying data from the rover to Earth. The lander was also equipped with a meteorology station. Over 2.5 meters of solar cells on the lander petals, in combination with rechargeable batteries, powered the lander and its onboard computer. Three low-gain antennas extended from three corners of the box and a camera extended up from the center on a 0.8-meter high pop-up mast. Images were taken and experiments performed by the lander and rover until 27 September 1997 when communications were lost for unknown reasons.

The landing site in the Ares Vallis region of Mars is at 19.33 N, 33.55 W. The lander has been named the Sagan Memorial Station, and it operated nearly three times its design lifetime of 30 days.

Pathfinder's Landing Spot

The Ares Vallis region of Mars is a large flood plain near Chryse Planitia. This region is one of the largest outflow channels on Mars, the result of a huge flood (possibly an amount of water equivalent to the volume of all five Great Lakes) over a short period of time flowing into the martian northern lowlands.

The Mars Pathfinder mission cost approximately $265 million including launch and operations. Development and construction of the lander cost $150 million and the rover about $25 million.

Edited and updated by Carolyn Collins Petersen.