On December 4, 1996, Mars Pathfinder, a robotic spacecraft that was designed primarily to demonstrate a low-cost way of delivering a set of science instruments and a free-ranging rover (Sojourner) to the Martian Surface was launched from Cape Canaveral on top of a Delta II rocket.

December 4 story of what happened this day in Science, Technology, Astronomy, and Space Exploration history.

Mars Pathfinder (lander) and Sojourner (rover)

The mission consisted of a lander (later renamed the Carl Sagan Memorial Station) and a lightweight, just 10.6 kg (23 lb) wheeled robotic Mars rover named Sojourner, which became the first rover to operate outside the Earth-Moon system. For comparison, Curiosity is a car-sized rover and it weighs 899 kg (1,982 lbs). Perseverance is even heavier at 1,025 kg (2,260 lbs).

Mission objectives

The mission objectives of Mars Pathfinder were:

  • To prove that the development of a “faster, better, and cheaper” spacecraft was possible. The development of the lander and the rover took just three years with a cost of under $150 million for the lander, and $25 million for the rover).
  • To show that it was possible to send a load of scientific instruments to another planet with a simple system and at one-fifteenth the cost of a Viking mission. Viking missions cost $935 million in 1974 or $3.5 billion in 1997 dollars.
  • To demonstrate NASA’s commitment to low-cost planetary exploration by finishing the mission with a total expenditure of $280 million, including the launch vehicle and mission operations.

Landing on Mars

Mars pathfinder landed on Mars on July 4, 1997, and delivered the Sojourner rover to the Martian surface the next day, on July 5, 1997. Sojourner became the first wheeled vehicle to rove on a planet other than Earth.

The landing site was an ancient flood plain in Mars’s northern hemisphere called “Ares Vallis” (“the valley of Ares”, the ancient Greek god of war and courage, equivalent of the ancient Roman deity Mars).

Stowed within a set of airbags, the lander impacted on the surface at a velocity of about 14 meters per second (about 50 km/h or 31 mph) generating about 18 g’s of deceleration. The package bounced at least 15 times before coming to rest, after which the airbags deflated revealing the lander.

Mars Pathfinder Lander and the Sojourner Rover on Mars
NASA’s Mars Pathfinder Lander and the Sojourner Rover on Mars. Image source: NASA Solar System Exploration website

Sojourner was designed for a mission lasting 7 sols (a sol is a martian day which is slightly longer than an Earth day, approximately 24 hours, 39 minutes, 35 seconds). But, it remained operational for 83 sols (85 Earth days).

Sojourner communicated with Earth through the Mars Pathfinder base station. The last successful communication with the rover was established at 3:23 a.m. PDT on September 27, 1997. The Martian rover traveled just over 100 meters (330 ft) by the time communication was lost.

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

The final contact with the Mars Pathfinder was established at 10:23 UT on September 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.

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

Sojourner on Mars surface
[Detail from the photo above] Robotic rover Sojourner on the Martian surface. It became the first wheeled vehicle on the surface of another planet.
Mars Pathfinder delivers Sojourner
The Sojourner rover and undeployed ramps onboard the Mars Pathfinder spacecraft can be seen in this image, by the Imager for Mars Pathfinder (IMP) on July 4, 1997 (Sol 1). Photo source: NASA

Sources and Further Reading

M. Özgür Nevres

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