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'''''Mars Pathfinder'''''
Launched on December 4, 1996, by [[NASA]] aboard a [[Delta II]] booster a month after the ''[[Mars Global Surveyor]]'', it landed on July 4, 1997, on [[Mars]]'s [[Ares Vallis]], in a region called [[Chryse Planitia]] in the [[Oxia Palus quadrangle]]. The [[lander (spacecraft)|lander]] then opened, exposing the rover which conducted many experiments on the Martian surface. The mission carried a series of scientific instruments to analyze the Martian [[Celestial body atmosphere|atmosphere]], [[climate]], and geology and the composition of its [[rock (geology)|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 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]]. The project manager was JPL's [[Tony Spear]].
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This mission was the first of a series of missions to Mars that included rovers, and was the first successful lander since the two ''[[Viking program|Vikings]]'' landed on Mars in 1976. Although the [[Soviet Union]] successfully sent rovers to the Moon as part of the [[Lunokhod program]] in the 1970s, its attempts to use rovers in its [[Mars 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 Rover]] mission. The ''Mars Pathfinder'' was also remarkable for its extremely low cost relative to other robotic space missions to Mars. Originally, the mission was conceived as the first of the [[Mars Environmental Survey]] (MESUR) program.<ref>{{cite news |last=Sawyer |first=Kathy |newspaper=[[Washington Post]] |title=One Way or Another, Space Agency Will Hitch a Ride to Mars |date=November 13, 1993 |url=https://www.washingtonpost.com/archive/politics/1993/11/13/one-way-or-another-space-agency-will-hitch-a-ride-to-mars/c3c354a0-59d1-4373-aa88-15d8b5a3f602/ |access-date=March 6, 2023 }}</ref>
==Mission objectives==
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==Science experiments==
[[File:Sojourner on Mars PIA01122.jpg|thumb|left|200px|''Sojourner'' rover on Mars on sol 22]]
The ''Mars Pathfinder'' conducted different investigations on the Martian soil using three scientific instruments. The lander contained a [[stereo camera|stereoscopic camera]] with spatial filters on an expandable pole called Imager for Mars Pathfinder (IMP),<ref>{{Cite journal|title= The imager for Mars Pathfinder experiment|author1=Smith, P. H. |author2=Tomasko, M. G. |author3=Britt, D. |author4=Crowe, D. G. |author5=Reid, R. |author6=Keller, H. U. |author7=Thomas, N. |author8=Gliem, F. |author9=Rueffer, P. |author10=Sullivan, R. |author11=Greeley, R. |author12=Knudsen, J. M. |author13=Madsen, M. B. |author14=Gunnlaugsson, H. P. |author15=Hviid, S. F. |author16=Goetz, W. |author17=Soderblom, L. A. |author18=Gaddis, L. |author19=Kirk, R. |journal=[[Journal of Geophysical Research]] |volume= 102 |issue=E2 |pages=4003–4026 |date=1997 |doi=10.1029/96JE03568 |bibcode=1997JGR...102.4003S|doi-access=free }}</ref><ref>{{Cite journal |title=Results from the Mars Pathfinder camera |author1=Smith P. H. |author2=Bell J. F. |author3=Bridges N. T. |journal=[[Science (journal)|Science]] |volume= 278|issue=5344 |pages=1758–1765|date=1997| doi=10.1126/science.278.5344.1758|pmid=9388170|bibcode = 1997Sci...278.1758S |doi-access=free }}</ref> and the Atmospheric Structure Instrument/Meteorology Package (ASI/MET)<ref>{{Cite journal| title= The Mars Pathfinder atmospheric structure investigation meteorology (ASI/MET) experiment|author1=Schofield J. T. |author2=Barnes J. R. |author3=Crisp D. |author4=Haberle R. M. |author5=Larsen S. |author6=Magalhaes J. A. |author7=Murphy J. R. |author8=Seiff A. |author9=Wilson G. |journal= Science|volume= 278|issue=5344|pages= 1752–1758|date= 1997| doi= 10.1126/science.278.5344.1752| pmid= 9388169|bibcode = 1997Sci...278.1752S |doi-access=free }}</ref> which
The ''[[Sojourner (rover)|Sojourner]]'' rover had an Alpha Proton X-ray Spectrometer ([[APXS]]),<ref>{{Cite journal |title=Determination of the chemical composition of Martian soil and rocks: The alpha proton X ray spectrometer |author1=R. Rieder |author2=H. Wänke |author3=T. Economou |author4=A. Turkevich |journal= Journal of Geophysical Research |date= 1997 |volume= 102 |issue=E2 |pages=4027–4044 |doi=10.1029/96JE03918 |bibcode=1997JGR...102.4027R|doi-access=free }}</ref> 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 investigate 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 [[mechanics|mechanical]] properties of the land, as well as the magnetic properties of the dust, atmosphere and the [[rotation]]al and [[orbit]]al dynamics of the planet.
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==== [[Celestial body atmosphere|Atmospheric]] and [[Meteorology|meteorological]] sensors (ASI/MET) ====
[[File:Mars Pathfinder lander scheme.jpg|thumb|Mars Pathfinder lander scheme. ASI/MET pole is visible extending towards the top.]]
The ASI/MET
===''Sojourner'' rover===
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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 {{Coord|19.13|N|33.22|W|globe:Mars|display=inline,title}},<ref>{{cite web | url=http://mpfwww.jpl.nasa.gov/MPF/science/geology.html | title=Mars Pathfinder Science Results | work=NASA | access-date=June 9, 2008 | archive-url=https://web.archive.org/web/20080920093840/http://mpfwww.jpl.nasa.gov/MPF/science/geology.html | archive-date=September 20, 2008 | url-status=dead }}</ref> succeeded, the lander received the name ''The [[Carl Sagan]] Memorial Station'' in honor of the [[astronomer]].<ref>{{cite web|title=Mars lander renamed for Sagan|url=https://www.jpl.nasa.gov/releases/97/sagansta.html|publisher=NASA|access-date=September 5, 2017|archive-url=https://web.archive.org/web/20181211162346/https://www.jpl.nasa.gov/releases/97/sagansta.html|archive-date=December 11, 2018|url-status=live}}</ref> (See also [[List of extraterrestrial memorials]])
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==Entry, descent and landing==
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[[File:Pathfinder Air Bags - GPN-2000-000484.jpg|thumb|right|200px|The ''Pathfinder'' air bags are tested in June 1995]]
Once the lander was {{cvt|355|m|ft}} above the ground, airbags were inflated in less than a second using three gas generators.<ref>{{Cite web|title=Mars Pathfinder Lander Description|url=https://pdsimage2.wr.usgs.gov/Missions/Mars_Pathfinder/mpim_0001/document/insthost.htm|access-date=31 March 2021|website=pdsimage.wr|publisher=[[USGS]]|archive-date=March 11, 2021|archive-url=https://web.archive.org/web/20210311004210/https://pdsimage2.wr.usgs.gov/Missions/Mars_Pathfinder/mpim_0001/document/insthost.htm|url-status=dead}}</ref> The airbags were made of four inter-connected multi-layer [[vectran]] bags that surrounded the tetrahedron lander. They were designed and tested to accommodate grazing angle impacts as high as {{cvt|28|m/s|mph}}. However, as the airbags were designed for no more than about {{cvt|15|m/s|mph}} vertical impacts, three solid retrorockets were mounted above the lander in the backshell.<ref>{{Cite web|title=Rocket Assisted Descent – The RAD Rocket Motors|url=https://mars.nasa.gov/MPF/mpf/rad.html|access-date=2021-02-16|website=mars.nasa.gov}}</ref> These were fired at {{cvt|98|m|ft}} 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 zero between {{cvt|15|and|25|m|ft}} above the ground. After 2.3 seconds, while the rockets were still firing, the lander cut the bridle loose about {{cvt|21.5|m|ft}} 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 {{cvt|14|m/s|mph}} and limited the impact to only 18 G of deceleration. The first bounce was {{cvt|15.7|m|ft}} high and continued bouncing for at least 15 additional bounces (accelerometer data recording did not continue through all of the bounces).<ref>{{Cite journal|last1=Spencer|first1=David A.|last2=Blanchard|first2=Robert C.|last3=Braun|first3=Robert D.|last4=Kallemeyn|first4=Pieter H.|last5=Thurman|first5=Sam W.|date=March 1998|title=Mars Pathfinder Entry, Descent, and Landing Reconstruction|url=http://dx.doi.org/10.2514/2.3478|journal=Journal of Spacecraft and Rockets|volume=36|issue=3|pages=357–366|doi=10.2514/2.3478|issn=0022-4650}}</ref>
The entire entry, descent and landing process was completed in four minutes.
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.
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 {{cvt|19|km|mi}} southwest of the center of the {{cvt|200|km|mi}} wide landing site ellipse. During [[Timekeeping on Mars#Sols|Sol]] 1, the first Martian solar day the lander spent on the planet, the lander took pictures and made some meteorological measurements. Once the data was received, the engineers realized that one of the airbags had not 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.<ref name=nssdca>{{Cite web|title=NASA – NSSDCA – Spacecraft – Details|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-068A|access-date=2021-02-16|website=nssdc.gsfc.nasa.gov}}</ref>
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The lander sent more than 2.3 billion bits (287.5 megabytes) of information including 16,500 pictures and made 8.5 million measurements of the [[atmospheric pressure]], temperature and wind speed.<ref name=jplpathfinder>{{cite web|url=http://www.nasa.gov/mission_pages/mars-pathfinder/|title=Mars Pathfinder and Sojourner|work=NASA|access-date=June 10, 2015|archive-url=https://web.archive.org/web/20150623112234/http://www.nasa.gov/mission_pages/mars-pathfinder/|archive-date=June 23, 2015|url-status=live}}</ref>
By taking multiple images of the sky at different distances from the Sun, scientists were able to determine that the size of the particles in the pink haze was about one [[micrometre]] 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.<ref>Smith, P. et al. 1997. "Results from the Mars Pathfinder Camera" ''Science'': 278. 1758–1765</ref> ''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 possibly cemented with [[ferric oxide]] (Fe<sub>2</sub>O<sub>3</sub>).<ref>Hviid, S. et al. 1997. "Magnetic Properties Experiments on the Mars Pathfinder Lander: Preliminary Results". ''Science'':278. 1768–1770.</ref> Using much more sophisticated instruments, [[Spirit Rover|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
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 {{cvt|1300|and|2000|km|mi}} in radius.<ref name="Golombek, M 1997">Golombek, M. et al. 1997. "Overview of the Mars Pathfinder Mission and Assessment of Landing Site Predictions". ''Science''. Science: 278. pp. 1743–1748</ref>
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