Mars Pathfinder

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Missing image
Artist's conception of the Mars Pathfinder on Mars

Characteristics of the mission:
Name Mars Pathfinder
Nation United States
Objective(s) To land on Mars
and perform Rover operations.
Craft Mars Pathfinder
Craft – Weight 870 kg
Administration and
planning of mission
Launch vehicle Delta 7925 (#D240)
Date and time
of launch
4 December 1996 at 06:58:07 UTC
Launched from ESMC / launch complex 17B
Mars Pathfinder Lander:
  1. Imager for Mars Pathfinder (IMP),
    (includes magnetometer and anemometer)
  2. Alpha Proton X-ray Spectrometer (APXS)
  3. Atmospheric and meteorological sensors (ASI/MET)

Rover Sojourner:

  1. Imaging system (three cameras)
  2. Laser drill
  3. Accelerometers
  4. Potentiometers

The Mars Pathfinder was launched on December 4, 1996 by NASA aboard a Delta II rocket, just a month after the Mars Global Surveyor was launched. After a 7-month voyage it landed on Ares Vallis, in a region called Chryse Planitia on Mars, on 4 July 1997. During its voyage the spacecraft had to accomplish four flight adjustments on 10 January, 3 February, 6 May and 25 June. The lander opened exposing the rover called Sojourner (named after the famous American abolitionist Sojourner Truth) which would go on to execute different experiments on Mars surface.

The mission carried a series of different scientific instruments to analyze the martian atmosphere, climate, geology and the composition of its rocks and soil. It was the second project from NASA's Discovery Program, which promotes the use of low-cost spacecraft and frequent launches under the motto "cheaper, faster and better" promoted by the then administrator, Daniel Goldin. The mission was directed by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology, responsible for NASA's Mars Exploration Program.

This mission to Mars, besides being the first of a series of missions to Mars that included rovers (robotic exploration vehicles), was the most important since the Vikings landed on the red planet in 1976, and also was the first mission to send a rover to the surface of another planet.

Though completely successful and completing real objectives, the Mars Pathfinder mission can be regarded as a "proof-of-concept" for various technologies, such as airbag-mediated touchdown and automated obstacle avoidance, both later exploited by the Mars Exploration Rovers. The Mars Pathfinder was also remarkable for its extremely low price, relative to other unmanned space missions. This was an important consideration, having in mind that approximately two-thirds of the spacecrafts destined to Mars have either failed to launch or were lost en route (See Mars Climate Orbiter in particular.)


Landing Site

The landing site was an ancient flood plain in Mars' northern hemisphere called "Ares Vallis" and is among the rockiest parts of Mars. It was chosen because scientists found it to be a relatively safe surface to land on and one which contained a wide variety of rocks deposited during a catastrophic flood. Upon successful landing, the landing site was named The Carl Sagan Memorial Station in honor of the late astronomer and leader in the field of unmanned space exploration.

The Probe

The probe consisted of a lander and a lightweight (10.6 kilograms/23 pounds) wheeled robot (Rover) called Sojourner ("one in a break from journeying"), after the sometime slave, abolitionist, and women's-rights activist Sojourner Truth.

Landing Process

Mars Pathfinder used an innovative method of directly entering the Martian atmosphere, assisted by a parachute to slow its descent through the thin Martian atmosphere and a giant system of airbags to cushion the impact.


The lander relayed transmissions to and from the robot, allowing it to operate independently of the probe body. The robot was remotely controlled, but had a basic camera-assisted autonomous control system allowing it to navigate and negotiate minor obstacles without operator intervention.

The robot's freedom of movement allowed the exploration team to closely analyze many more rocks and soil samples than with a traditional probe. From its landing in July 4, 1997 until the final data transmission on September 27, 1997, Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that Mars was at one time in its past warm and wet, with water existing in its liquid state and a thicker atmosphere.

The exact reason for the final failure of the lander is not certain, but probably it was a failure of a battery, resulting in night-time cooling of the spacecraft that would render it inoperable. The rover was instructed by automatic backup procedures to return to the lander, but its exact location and state are unknown. However, the lander and rover performed much longer and better than expected. NASA efforts to recontact Pathfinder ended March 10, 1998.

Mars Pathfinder Objectives

  • To prove that the development of "faster, better and cheaper" spacecraft is possible (with three years for development and a cost under US$150 millions).
  • To show that it is possible to send a load of scientific instruments to another planet with a simple system and at one fifth the cost of a Viking mission.
  • To demostrate NASA's commitment to low-cost planetary exploration finishing the mission with a total expenditure of US$280 millions, including the launch vehicle and mission operations.

Mission's workings

The Mars Pathfinder realized different investigations on the martian soil through three scienticfic instruments. The lander contained a stereoscopic camera with spacial filters on a expandable pole called Imager for Mars Pathfinder (IMP) and the Atmospheric Structure Instrument/Meteorology Package (ASI /MET) which acts as a Mars metereologic station, collecting data about pressure, temperature and winds. The Sojourner rover had a Alpha Proton X-ray Spectrometer (APXS), which was used to analyze the components of the rocks and soil. The rover also had two black and white cameras and a color one. These instruments could make investigations regarding the geology of Mars surface from just a few milimeters to many hundreds of meters, the geochemistry and evolutionary history of the rocks and surface, the magnetic and mechanic properties of the land, besides the magnetic ones from the dust, atmosphere and the rotational and orbital dynamics of the planet.

Mars Pathfinder scientific objectives

  • Surface morphology and geology to a metric scale.
  • Petrology and geochemistry of superficial materials.
  • Magnetic and mechanic properties of the surface.
  • Atmospheric structure, besides diurnal and nocturnal metereologic variations.
  • Rotational and orbital dynamics of Mars.

Mission Stages: entry, descent and landing

Mars Pathfinder's landing was just as it had been designed by NASA's engineers.
Mars Pathfinder's landing was just as it had been designed by NASA's engineers.

During the entry stages these devices were used: termic-protection shield and a big braking parachute; the usage of an altimeter radar so that the lander could establish how far it was from the surface; retrorockets to slow-down the lander during its descent; lastly, 24 airbags were opened 8 seconds before impact to muffle the landing once the lander detached from its parachute. Its landing speed was about 10.6 metres per second. The whole process was completed in 4 minutes.

Once the lander was placed on the surface, the airbags deflated and retracted with the lander over its base; finally the petals with the solar panels were deployed. The lander arrived at night at 2:56:55 a.m. local time (16:56:55 UTC), so the lander had to wait until sunrise to send its first signals to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, some 19 kilometres southwest from the planned site. During Sol 1 –that's how martian days are called– the lander took pictures and made some metereologic measurements. Once the data was received, the engineers realized that one of the airbags hadn't fully deflated and could be a problem for the forthcoming traverse of Sojourner's descent ramp. To solve the problem, they made the lander to raise and lower one of its petals several times to flatten the airbag. The procedure was a success.

The Sojourner gets out

Sojourner's exit from the lander occurred on Sol 2. As the next sols progressed it approached some rocks which were named (by the scientists) "Barnacle Bill", "Yogi" and "Scooby Doo", after the famous cartoons. The rover made measurements of the elements found in those rocks and in the martian soil, while the lander took pictures of the Sojourner and the surrounding terrain, besides making climate observations.

The Sojourner was a six-wheeled vehicle and it was 65 cm long, 48 cm wide, 30 cm tall and weighed 10.6 kg. It could move about 500 metres from the lander and its maximun speed reached 1 centimeter per second. During its 83 days of operation, it sent 550 photographs to Earth and analyzed the chemical properties of sixteen locations near the lander.

Sojourner's rock analysis

The Sojourner Rover is taking its Alpha Proton X-ray Spectrometer measurement of Yogi the Rock (NASA)
The Sojourner Rover is taking its Alpha Proton X-ray Spectrometer measurement of Yogi the Rock (NASA)

The first analysis on a rock started on Sol 3 with "Barnacle Bill". The Alpha Proton X-ray Spectrometer (APXS) was used to determine its composition, the spectrometer needed 10 hours to make a full scan of the sample. It found all the elements except for hydrogen, which constitutes just one tenth of the 1% of the rock's or soil's mass. The APXS works by radiating rocks ans soil samples with alpha particleshelium nuclei (formed by two protons and two neutrons). The results indicated that "Barnacle Bill" is much like Earth's andesites, confirming past volcanic activity.

Analysis on "Yogi" rock using again the APXS showed a different composition for this rock, it was a basaltic rock, more promitive than "Barnacle Bill". Yogi's shape and texture show that it was probably deposited there by a flood.

Another rock, named "Moe", was found to have certain marks on the surface, demostrating erosion caused by the wind. Most rocks analyzed showed a high content of silicon. In another region known as Rock Garden the Sojourner encountered crescent Moon-shaped dunes, which are similar to crescentic dunes on Earth.

The lander, on the other hand, sent more than 16,500 pictures and made 8.5 million measurements of the atmospheric pressure, temperature and wind speed.

End of the mission

Although the mission was programmed to last a week to a month, these limits were exceeded by 3 times and 12 times, respectively. The final contact with the Pathfinder was at 10:23 UTC on September 27, 1997. Although the mission planners tried to restore contact during the following five months, the successful mission was terminated March 10, 1998. After the landing, the Mars Pathfinder was renamed as the Sagan Memorial Station in honor of the famous astronomer and planetologist Carl Sagan. In total, the mission exceeded in a few days its goals.


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

Related articles


  • Mars Pathfinder Litograph Set, NASA. (1997)
  • Poster: Mars Pathfinder –Roving the Red Planet, NASA. (1998)
  • Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Asif A. Siddiqi. Monographs in Aerospace History, #24. June 2002, NASA History Office.
  • "Return to Mars", article by William R. Newcott. National Geographic, pp. 2-29. Vol. 194, 2nd edition - August 1998.
  • "La misión Pathfinder –rebautizada Carl Sagan Memorial Station, en memoria del célebre astrónomo-, paso a paso todo Marte", de J. Roberto Mallo. Conozca Más, págs. 90-96. Edición número 106 - agosto de 1997.
  • "Un espía que anda por Marte", de Julio Guerrieri. Descubrir, págs. 80-83. Edición número 73 - agosto de 1997.
  • "Mars Pathfinder: el inicio de la conquista de Marte" EL Universo, Enciclopedia de la Astronomía y el Espacio, Editorial Planeta-De Agostini, págs. 58-60. Tomo 5. (1997)

Bibliography on Mars

  • The New Solar System, J. Kelly Beatty, Carolyn Collins Petersen, Andrew Chaikin. Cambridge University Press; 4 edition (1998); ISBN 0521645875
  • The Surface of Mars, Michael H. Carr. Yale University Press, New Haven; 1 edition (1981); ISBN 0300027508, ISBN 0300032420
  • Exploring the Planets, Eric H. Christiansen, Kenneth W. Hamblin. Prentice-Hall, Englewood Cliffs, New Jersey; 2 edition (1995); ISBN 0023224215
  • The Search for Life on Mars: Evolution of an Idea, Henry S.F. Cooper. Holt, Rinehart, and Winston, New York (1980); ISBN 0030461669 (hardcover), ISBN 0030598184
  • Mars, Percival Lowell. Houghton, Mifflin, Boston, New York (1895). Kessinger Publishing (2004); ISBN 1419132849
  • Journey Into Space: The First Thirty Years of Space Exploration, Bruce Murray. W.W. Norton, New York (1989); ISBN 0393026752 (hardcover), ISBN 0393307034
  • Planets & Perception: Telescopic Views and Interpretations, 1609-1909, William Sheehan. University of Arizona Press, Tucson (1988); ISBN 0816510598
  • The Planet Mars: A History of Observation and Discovery, William Sheehan. University of Arizona Press, Tucson (1996); ISBN 0816516405 (hardcover), ISBN 0816516413
  • The Martian Landscape, Viking Lander Imaging Team. NASA SP-425 (1978)
  • Viking Orbiter Views of Mars, Viking Orbiter Imaging Team. NASA SP-441 (1980)
  • Mars Beckons, John Noble Wilford. ISBN 0394583590 (hardcover, 1 edition, 1990), ISBN 0679735313 (1991), ISBN 0517198037 (1997)

External links

da:Mars Pathfinder de:Pathfinder ja:マーズ・パスファインダー nl:Mars_Pathfinder pt:Mars Pathfinder sv:Pathfinder (Marslandare) zh:火星探路者


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