Mars Pathfinder

Mars Pathfinder

Operator	NASA – JPL
Mission type	Lander, rover
Orbital insertion date	Landed July 4, 1997 UT 16:57
Launch date	December 4, 1996 at 06:58:07 UTC from ESMC / launch complex 17B
Launch vehicle	Delta 7925 (#D240)
COSPAR ID	1996-068A
Mass	264 kg (lander), 10.5 kg (rover)
Power	35 W (lander) 13 W (rover)

The Mars Pathfinder (MESUR Pathfinder^[1]), later renamed the Carl Sagan Memorial Station, was launched on December 4, 1996 by NASA aboard a Delta II 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, in the Oxia Palus quadrangle, on July 4, 1997. During its voyage the spacecraft had to accomplish four flight adjustments on January 10, 3January, February6 May and June 25. The lander opened, exposing the rover called Sojourner that would go on to execute many experiments on the Martian surface.

The mission carried a series of 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 successful mission to send a rover to a planet. The then still extant Soviet Union successfully sent rovers to the Moon as part of the Lunokhod programme in the 1970s, but its two attempts to send rovers in the Mars probe program failed.

In addition to scientific objectives, the Mars Pathfinder mission was also 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 to Mars. Originally, the mission was conceived as the first of the Mars Environmental Survey (MESUR) program.

Mission objectives

• To prove that the development of "faster, better and cheaper" spacecraft is possible (with three years for development and a cost under $150 million).
• To show that it is 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. (For comparison, the Viking missions cost $935 million in 1974^[2] 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.

The project manager was Tony Spear.

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 slave and abolitionist Sojourner Truth. [1] (See below for the selection of the name.)

Mission equipment

1990s concept illustration of lander and rover

Mars Pathfinder lander IMP

Actual 1997 image from the IMP after landing on Mars

The Mars Pathfinder executed different investigations on the Martian soil using three scientific instruments. The lander contained a stereoscopic camera with spatial filters on an expandable pole called Imager for Mars Pathfinder (IMP),^[3][4] and the Atmospheric Structure Instrument/Meteorology Package (ASI /MET)^[5] which acts as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure included three windsocks mounted at three heights on a pole, the topmost at about one meter (yard) and generally registered winds from the West.^[6]

The Sojourner rover had a Alpha Proton X-ray Spectrometer (APXS),^[7] 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 of the geology of the Martian surface from just a few millimeters to many hundreds of meters, the geochemistry and evolutionary history of the rocks and surface, the magnetic and mechanical properties of the land, as well as the magnetic properties of the dust, atmosphere and the rotational and orbital dynamics of the planet.

Mars Pathfinder Lander:

1. Imager for Mars Pathfinder (IMP), (includes magnetometer and anemometer)
2. Atmospheric and meteorological sensors (ASI/MET)

Mars Pathfinder Sojourner Rover:

1. Imaging system (three cameras: front B&W stereo, 1 rear color)
2. Laser striper hazard detection system
3. Alpha Proton X-ray Spectrometer (APXS)
4. Wheel Abrasion Experiment
5. Material Adherence Experiment
6. Accelerometers
7. Potentiometers

Other results from Pathfinder

The magnet array experiment carried aboard the Mars Pathfinder Mission was developed by the Niels Bohr Institute lead by Jens Martin Knudsen.

By taking multiple images of the sky at different distances from the sun, scientists were able to determine that size of the particles in the pink haze was about 1 micrometer in radius. The color of some soils was similar to that of an iron oxyhydroxide phase which would support the theory of a warmer and wetter climate in the past. ^[8] Pathfinder carried a series of magnets to examine the magnetic component of the dust. Eventually, all but one of the magnets developed a coating of dust. Since the weakest magnet did not attract any soil, it was concluded that the airborne dust did not contain pure magnetite or just one type of maghemite. The dust probably was an aggregate possible cemented with ferric oxide (Fe₂O₃).^[9] Using much more sophisticated instruments, Mars Spirit Rover found that magnetite could explain the magnetic nature of the dust and soil on Mars. Magnetite was found in the soil and that the most magnetic part of the soil was dark. Magnetite is very dark.^[10]

Using Doppler tracking and two-way ranging, scientists added earlier measurements from the Viking landers to determine that the non-hydrostatic component of the polar moment of inertia is due to the Tharsis bulge and that the interior is not melted. The central metallic core is between 1300 km and 2000 km in radius.^[11]

Landing site

Mars Pathfinder seen from space by the MRO HiRISE.

The landing site was an ancient flood plain in Mars's northern hemisphere called "Ares Vallis" ("the valley of Ares," the Ancient Greek equivalent of the Ancient Roman deity Mars) and is among the rockiest parts of Mars. Scientists chose it because they found it to be a relatively safe surface to land on and one that contained a wide variety of rocks deposited during a catastrophic flood. After the landing, at ,^[12] succeeded, the landing site received the name The Carl Sagan Memorial Station in honor of the late astronomer and leader in the field of robotic spacecraft missions.

Entry, descent and landing process

Mars Pathfinder entered the Martian atmosphere and landed using an innovative system involving an entry capsule, a supersonic parachute, followed by solid rockets and large airbags to cushion the impact.

Mars Pathfinder directly entered Mars atmosphere in a retrograde direction from a hyperbolic trajectory at 6.1 km/s using an atmospheric entry aeroshell (capsule) that was derived from the original Viking Mars lander design. The aeroshell consisted of a back shell and a specially designed ablative heatshield to slow to 370 m/s (830 MPH) where a supersonic disk-gap-band parachute was inflated to slow its descent through the thin Martian atmosphere to 68 m/s (about 160 MPH). The lander's on-board computer used redundant on-board accelerometers to determine the timing of the parachute inflation. Twenty seconds later the heatshield was pyrotechnically released. Another twenty seconds later the lander was separated and lowered from the backshell on a 20 m bridle (tether). When the lander reached 1.6 km above the surface, a radar was used by the on-board computer to determine altitude and descent velocity. This information was used by the computer to determine the precise timing the landing events that followed.

The Pathfinder air bags are tested in June 1995

Once the lander was 355 m above the ground, airbags were inflated in less than a second using three catalytically cooled solid rocket motors that served as gas generators. The airbags were made of 4 inter-connected multi-layer vectran bags that surrounded the tetrahedron lander. They were designed and tested to accommodate grazing angle impacts as high as 28 m/s. However, as the airbags were designed for no more than about 15 m/s vertical impacts, three solid retrorockets were mounted above the lander in the backshell. These were fired at 98 m above the ground. The lander's on-board computer estimated the best time to fire the rockets and cut the bridle so that the lander velocity would be reduced to about 0 m/s between 15 and 25 m above the ground. After 2.3 seconds, while the rockets were still firing, the lander cut the bridle loose about 21.5 m above the ground and fell to the ground. The rockets flew up and away with the backshell and parachute (they have since been sighted by orbital images). The lander impacted at 14 m/s and limited the impact to only 18 G of deceleration. The first bounce was 15.7 m high and continued bouncing for at least 15 additional bounces (accelerometer data recording did not continue through all of the bounces).

The entire entry, descent and landing (EDL) process was completed in 4 minutes.^[13]

Once the lander stopped rolling, the airbags deflated and retracted toward the lander using four winches mounted on the lander "petals". Designed to right itself from any initial orientation, the lander happened to roll right side up onto its base petal. 74 minutes after landing, the petals were deployed with Sojourner rover and the solar panels attached on the inside.

The lander arrived at night at 2:56:55 Mars local solar time (16:56:55 UTC) on July 4, 1997. The lander had to wait until sunrise to send its first digital signals and images to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, only 19 kilometres southwest of the center of the 200 km wide landing site ellipse. During Sol 1 –or martian days– 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 sent commands to the lander to raise one of its petals and perform additional retraction to flatten the airbag. The procedure was a success and on Sol 2, Sojourner was released, stood up and backed down one of two ramps.

Pathfinder lands

Mars Pathfinder panorama of landing site taken by IMP

Sojourner rover

The Sojourner rover was the second space exploration rover to successfully reach another planet, and the first to actually be deployed on another planet. Sojourner landed on Mars as part of the Mars Pathfinder mission on July 4, 1997.

The on-board computer

The embedded computer on board the Sojourner rover was based around the 100 kHz Intel 80C85 CPU with 512 KB of RAM and 176 KB of flash memory solid-state storage.^[14]

The Sojourner gets out

Sojourner rover

Sojourner's exit from the lander occurred on Sol 2, after its landing in July 4, 1997. 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 is a six-wheeled 65 cm long vehicle, 48 cm wide, 30 cm tall and weighs 10.5 kg.^[15] When operating, it could move about 500 meters from the lander and its maximum speed reached one centimeter per second. During its 83 sols of operation, it sent 550 photographs to Earth and analyzed the chemical properties of sixteen locations near the lander.

Sojourner's rock analysis

Sojourner next to the rock "Barnacle Bill"

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 taking ten hours to make a full scan of the sample. It found all the elements except hydrogen, which constitutes just 0.1% of the rock's or soil's mass.

The APXS works by irradiating rocks and soil samples with alpha particles (helium nuclei, which consist of two protons and two neutrons). The results indicated that "Barnacle Bill" is much like Earth's andesites, confirming past volcanic activity. The discovery of andesites shows that some Martian rocks have been remelted and reprocessed. On Earth, Andesite forms when magma sits in pockets of rock while some of the iron and magnesium settle out. Consequently, the final rock contains less iron and magnesiums and more silica. Volcanic rocks are usually classified by comparing the relative amount of alkalis (Na₂O and K₂O) with the amount of silica (SiO₂). Andesite is different than the rocks found in meteorites that have come from Mars.^[11][16][17]

Analysis of "Yogi" rock again using the APXS showed that it was a basaltic rock, more primitive 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 its surface, demonstrating 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.

By the time that final results of the mission were described in a series of articles in the Journal Science 9, December 5, 1997), it was believed that the rock Yogi contained a coating of dust, but was similar to the rock Barnacle Bill. Calculations suggest that the two rocks contain mostly the minerals orthopyroxene (magnesium-iron silicate), feldspars (aluminum silicates of potassium, sodium, and calcium), quartz (silicon dioxide), with smaller amounts of magnetite, ilmenite, iron sulfide, and calcium phosphate.^[11][16][17]

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

Close-up of Mars sky at sunset, showing more color variation, as imaged by Mars Pathfinder

Although the mission was programed to last a week to a month, it eventually lasted for almost three months. 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 on 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. The mission had exceeded its goals in the first month.

The Mars Pathfinder entry descent and landing system design was used (with some modification) on the Mars Exploration Rover mission. Likewise many design aspects of Sojourner rover (e.g. the rocker-bogie mobility architecture and the navigation algorithms) were also successfully used on the Mars Exploration Rover mission.

Mars Reconnaissance Orbiter may have spotted Pathfinder in January 2007.^{[18] [19]}

Naming the rover

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

The name Sojourner was chosen for the Mars Pathfinder rover after a year-long, worldwide competition in which students up to 18 years old were invited to select a heroine and submit an essay about her historical accomplishments. The students were asked to address in their essays how a planetary rover named for their heroine would translate these accomplishments to the Martian environment.

Initiated in March 1994 by The Planetary Society of Pasadena, CA, in cooperation with NASA's Jet Propulsion Laboratory (JPL), the contest got under way with an announcement in the January 1995 issue of the National Science Teachers Association's magazine "Science and Children," which is circulated to 20,000 teachers and schools across the nation.

Valerie Ambroise, 12, of Bridgeport, CT, submitted the winning essay about Sojourner Truth, an African-American reformist who lived during the Civil War era. An abolitionist and champion of women's rights, Sojourner Truth, whose legal name was Isabella Van Wagener, made it her mission to "travel up and down the land," advocating the rights of all people to be free and the rights of women to participate fully in society. The name Sojourner was selected because it means "traveler." JPL scientists and engineers working on the Mars Pathfinder project and Planetary Society staff members reviewed the 3,500 total entries received from all over the world, including essays from students living in Canada, India, Israel, Japan, Mexico, Poland and Russia. Nearly 1,700 of the essays were submitted by students aged 5 to 18 years old.

The selection of winners from this group by representatives from JPL and NASA Headquarters was based on several factors: the quality and creativity of the essay, taking into consideration the age of each contestant, the appropriateness of the name for a Mars rover, and the knowledge of the heroine, and the understanding of the Pathfinder rover's mission conveyed in the essay.

The second place prize winner was Deepti Rohatgi, 18, of Rockville, MD, who proposed naming the rover after Marie Curie, a Polish-born chemist who won the Nobel Prize in 1911 for her discovery of the elements radium and polonium. The test model identical to Sojourner used on earth was named Marie Curie. The third place prize went to Adam Sheedy, 16, of Round Rock, TX, who chose the late astronaut Judith Resnik as his namesake for the new rover.

Honors

Wheel size comparison: Sojourner, Mars Exploration Rover, Mars Science Laboratory.

• On October 21, 1997, at the Geological Society of America's annual meeting in Salt Lake City, Utah, Sojourner was awarded honorary membership in the Planetary Geology Division of the society.^[20]
• In 2003, Sojourner was inducted into the Robot Hall of Fame.
• Images of Sojouner approaching Yogi Rock were used in the opening credits of the Star Trek: Enterprise science fiction television program, the first historical use in a science fiction film or television program of video taken on the surface of another planet.

See also

• Exploration of Mars
• Mars Exploration Rover
• Space exploration
• Atmospheric reentry
• Lunokhod programme

Notes

References

External links

• Mars Pathfinder NASA/JPL Website
• Mars Pathfinder Mission Profile by NASA's Solar System Exploration
• Ted Stryk's Mars Pathfinder page
• "A Crawl On Mars" – Ted Stryk's Sojourner rover page
• NASA Office of Space Science
• JPL – Mars Exploration Rover Mission
• Authoritative Account of MPF Reset Issue — discussion of the software problems on the Pathfinder spacecraft
• A Little Rock on Mars — children's story about the Pathfinder landing
• Sojourner rover replica (French) — description and images of a full scale functional replica of the Sojourner rover.
• Pathfinder landing site as seen from orbit by Mars Reconnaissance Orbiter

Spacecraft missions to Mars Flybys Mariner 4 · 6 · 7 · Mars 4 · Rosetta · Dawn Orbiters Mariner 9 · Mars 2 · 3 · 5 · Viking 1 · 2 · Phobos 2 · Mars Global Surveyor · 2001 Mars Odyssey · Mars Express · Mars Reconnaissance Orbiter Landers Mars 3 · Viking 1 · 2 · Mars Pathfinder · Phoenix Rovers Sojourner · Mars Exploration Rovers (Spirit · Opportunity) Future missions Mars Science Laboratory (2011) · Fobos-Grunt / Yinghuo 1 (2011) · MetNet (2011-2019) · Northern Light (2012) · MAVEN (2013) · Mars Trace Gas Mission (2016) · ExoMars static lander (2016) and rover (2018) · Mars Astrobiology Explorer-Cacher‎ (2018) · Mars sample return mission (2018+) · Manned mission (2030+) Related topics Exploration · Colonization · Failed Mars missions · Mars Scout Program Bold italics indicate active missions