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{{Short description|First NASA Mars rover on Mars Pathfinder mission}}
{{italic title}}
{{Infobox spaceflight
| name = ''Sojourner''
| image = Sojourner on Mars PIA01122.jpg
| image_caption = ''Sojourner'' rover pictured by ''Pathfinder'' lander
| insignia = Mars Pathfinder Insignia.png
| insignia_caption = ''Mars Pathfinder'' mission patch
| mission_type = [[Mars rover]]
| operator = [[NASA]]
| website = {{official|http://www.nasa.gov/mission_pages/mars-pathfinder/}}
| mission_duration = Planned: 7 [[martian day|sols]] (7&nbsp;days) Mission end: 83 sols (85&nbsp;days) From arrival on Mars
| manufacturer = 
| dry_mass = {{convert|11.5|kg|lb}} (rover only)
| launch_mass = 
| power =
| launch_date = December 4, 1996, 06:58:07&nbsp;UTC
| launch_rocket = [[Delta II]] 7925 D240
| launch_site = [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Launch Complex 17|LC-17B]]
| launch_contractor = [[McDonnell Douglas]]
| deployment_from = ''[[Mars Pathfinder]]''
| deployment_date = {{start-date|July 5, 1997}}
| last_contact = {{end-date|September 27, 1997}}
|interplanetary = 
 {{Infobox spaceflight/IP
 |type = rover
 |object = [[Mars]]
 |arrival_date = {{start date|1997|07|04}} 16:56:55 [[Coordinated Universal Time|UTC]]
 |location = [[Ares Vallis]], [[Chryse Planitia]], [[Mars]] {{Coord|19|7|48|N|33|13|12|W|globe:mars|name=Sojourner rover (Mars Pathfinder)}}
 |distance = {{Convert|100|m|ft}}
 }}
| programme = [[NASA]] Mars rovers
| next_mission = ''[[Spirit (rover)|Spirit]]''
}}

'''''Sojourner''''' is a robotic [[Mars rover]] that landed in the [[Ares Vallis]] channel in the [[Chryse Planitia]] region of the [[Oxia Palus quadrangle]] on July 4, 1997. ''Sojourner'' was operational on Mars for 92 [[Timekeeping on Mars#Sols|sols]] (95 Earth days). It was the first wheeled vehicle to rove on a planet other than Earth and formed part of the ''[[Mars Pathfinder]]'' mission.<ref>{{cite book|url=https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf|title=Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016|page=195|last1=Siddiqi|first1=Asif A.|author-link=Asif Azam Siddiqi|lccn=2017059404|isbn=9781626830424|publisher=NASA History Program Office|edition=second|year=2018|id=SP2018-4041|series=The NASA history series|location=Washington, DC|access-date=2019-11-04|archive-date=2019-12-08|archive-url=https://web.archive.org/web/20191208003521/https://www.nasa.gov/sites/default/files/atoms/files/beyond-earth-tagged.pdf|url-status=live}}</ref>

The rover was equipped with front and rear cameras, and hardware that was used to conduct several scientific experiments. It was designed for a mission lasting 7&nbsp;sols, with a possible extension to 30&nbsp;sols,<ref name="faq" /> and was active for 83&nbsp;sols (85 Earth days). The rover communicated with Earth through the ''Pathfinder'' base station, which had its last successful communication session with Earth at 3:23&nbsp;a.m. PDT on September 27, 1997.<ref name=sol86>{{cite web|url=https://mars.nasa.gov/MPF/ops/sol86.html|title=Mars Pathfinder – Mars – Sol 86 Images|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2020-10-26|archive-url=https://web.archive.org/web/20201026001047/https://mars.nasa.gov/MPF/ops/sol86.html|url-status=live}}</ref> The last signal from the rover was received on the morning of October 7, 1997.<ref name=sol92>{{cite web|url=https://mars.nasa.gov/MPF/ops/sol92.html|title=Mars Pathfinder – Mars – Sol 92 Images|website=mars.nasa.gov|access-date=2021-03-08|archive-date=2021-03-22|archive-url=https://web.archive.org/web/20210322192317/https://mars.nasa.gov/MPF/ops/sol92.html|url-status=live}}</ref>

''Sojourner'' traveled just over {{convert|100|m|ft|sp=us}} by the time communication was lost.<ref name="Sojourner">{{cite web|url=http://spacepioneers.msu.edu/robot_rovers/sojourner.html|title=Sojourner|url-status=dead|archive-url=https://web.archive.org/web/20150320062255/http://spacepioneers.msu.edu/robot_rovers/sojourner.html|archive-date=20 March 2015}}</ref> Its final confirmed command was to remain stationary until October 5, 1997, (sol 91) and then drive around the lander;<ref>{{cite web|url=https://mars.nasa.gov/MPF/ops/sol89.html|title=Mars Pathfinder – Mars – Sol 89 Images|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2020-08-14|archive-url=https://web.archive.org/web/20200814003920/https://mars.nasa.gov/MPF/ops/sol89.html|url-status=live}}</ref> there is no indication it was able to do so. The ''Sojourner'' mission formally ended on March 10, 1998, after all further options were exhausted.

== Mission ==
{{Main|Mars Pathfinder}}
[[File:Marspathrov.jpg|thumb|''Sojourner'' at JPL]]

''Sojourner'' was an experimental vehicle whose main mission was to test in the Martian environment technical solutions that were developed by engineers of the NASA research laboratories.<ref name="Matijevic2" /> It was necessary to verify whether the design strategy followed had resulted in the construction of a vehicle suitable for the environment it would encounter, despite the limited knowledge of it. Careful analysis of the operations on Mars would make it possible to develop solutions to critical problems identified and to introduce improvements for subsequent planetary exploration missions. One of the mission's main aims was to prove the development of "faster, better and cheaper" spacecraft was possible. Development took three years and cost under $150&nbsp;million for the lander, and $25 million for the rover; development was faster and less costly than all previous missions.<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=MESURPR |title=Mars Pathfinder Rover |publisher=NASA |access-date=2020-09-30 |archive-date=2020-10-21 |archive-url=https://web.archive.org/web/20201021135133/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=MESURPR |url-status=live }}</ref>

These objectives required careful selection of the landing site to balance the technical requests with the scientific ones.<ref name="landing site">{{cite journal|first1=M.P. |last1=Golombek | first2=R.A. |last2= Cook| first3= H.J. |last3= Moore| first4= T.J. |last4= Parker |title=Selection of the Mars Pathfinder landing site |journal=J. Geophys. Res. |volume=102 | number=E2 |pages=3967–3988 |year=1997 |doi=10.1029/96JE03318|bibcode=1997JGR...102.3967G |doi-access=free }}</ref> A large plain was needed for the probe to land and rocky terrain to verify the rover's systems. The choice fell on [[Ares Vallis]] in [[Chryse Planitia]], which is characterized by alluvial-looking rock formations. Scholars believed the analysis of the rocks, which lie in what appears to be the outlet of a huge drainage channel, could have confirmed the past presence of liquid water on the surface of Mars and provide details of the surrounding areas, from which the rocks were eroded.<ref name="landing site" /><ref name=Golombek97>{{cite journal |title=Overview of the Mars Pathfinder Mission and Assessment of Landing Site Predictions |journal=Science |year=1997 |volume=278 |number=5344 |pages=1743–1748 |first=M.P. |last=Golombek |doi=10.1126/science.278.5344.1743 |pmid=9388167 |bibcode=1997Sci...278.1743G |doi-access=free }}</ref>

== Technical characteristics ==
{{multiple image
| align = right
| direction = horizontal
| total_width = 400
| image1 = Mars Pathfinder lander scheme.jpg
| caption1 = Schematic representation of the lander
| alt = Schematic representation of Mars Pathfinder lander and rover
| image2 = Sojourner rover scheme.jpg
| caption2 = Schematic representation of the rover
}}

''Sojourner'' was developed by NASA's [[Jet Propulsion Laboratory]] (JPL). It is a six-wheeled, {{Convert|65|cm|inch|abbr=in|adj=on}} long, {{Convert|48|cm|inch|abbr=in|adj=on}} wide and {{Convert|30|cm|inch|abbr=in|adj=on}} high vehicle. In the mission's [[cruise phase]], it occupied an {{Convert|18|cm|inch|abbr=in|adj=on}} high space and has a mass of {{Convert|11.5|kg|lb|abbr=on}}.<ref name=dimensions>{{cite web |title=Mars Pathfinder |editor=NASA, JPL |url=https://mars.nasa.gov/internal_resources/815/ |access-date=24 September 2010 |archive-date=13 May 2013 |archive-url=https://web.archive.org/web/20130513063945/http://www.jpl.nasa.gov/news/fact_sheets/mpf.pdf |url-status=live }}</ref><ref name=ROW>{{cite web |url=http://marsprogram.jpl.nasa.gov/MPF/rover/mission.html |title=Rover Sojourner |editor=JPL, NASA |access-date=24 September 2010 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025222059/http://marsprogram.jpl.nasa.gov/MPF/rover/mission.html |url-status=live }}</ref> It was supported by a lander, a tetrahedron-shaped structure with a mass of {{Convert|250|kg|lb|abbr=on}}, and had a camera, scientific instrumentation, three petals of solar panels, a [[meteorology]] mast,<ref name=washington>{{cite web |url=https://www-k12.atmos.washington.edu/k12/mars/MPF_short_facts.html |title=JPL Mars Pathfinder Quick Facts |publisher=University of Washington |last=Tillman |first=J E |website=washington.edu |access-date=August 19, 2021 |archive-date=August 19, 2021 |archive-url=https://web.archive.org/web/20210819153052/https://www-k12.atmos.washington.edu/k12/mars/MPF_short_facts.html |url-status=live }}</ref> and {{Convert|6|kg|lb|abbr=on}} of equipment that was required to maintain communications between the rover and the lander.<ref name="ROW" /> Hardware included a steerable, high-gain [[X-band]] antenna that could send approximately 5.5 [[kilobit]]s per second into a {{Convert|70|meter|foot|abbr=on}} [[Deep Space Network]] antenna, {{Convert|3.3|sqm|sqft|abbr=on}} [[gallium-arsenide]] solar arrays that generated 1.1 [[Kilowatt-hour|kW⋅h]]/day and were capable of providing enough power to transmit for 2–4 hours per sol and maintain 128 megabytes of dynamic memory through the night.<ref name="NASA" />

=== Lander ===
[[File:Mars Pathfinder IMP camera.gif|thumb|Lander's IMP camera, see also [[:File:Diagram of Mars Pathfinder IMP camera.jpg|diagram of the IMP]].]]

One of the lander's main tasks was to support the rover by imaging its operations and sending data from the rover to Earth. The lander had rechargeable batteries and over {{Convert|2.5|meters|feet|abbr=on}} of solar cells on its petals.<ref name="nssdca" /> The lander contained a [[stereo camera|stereoscopic camera]] with [[spatial filter]]s 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 acted as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure included three [[windsock]]s mounted at three heights on a pole, the topmost at about {{Convert|1|m|ft|spell=in|abbr=out|sp=us}} and generally registered winds from the west.<ref>{{cite web |url=http://mars.jpl.nasa.gov/MPF/science/windsocks.html |title=Windsocks on Mars |work=JPL/NASA Mars Pathfinder |year=2005 |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20160305011341/http://mars.jpl.nasa.gov/MPF/science/windsocks.html |archive-date=March 5, 2016 |url-status=live }}</ref> To provide continuous data, the IMP imaged the windsocks once every daylight hour. These measurements allowed the [[eolian processes]] at the landing site, including the particle threshold and the aerodynamic surface roughness, to be measured.<ref name="washington" />

The square eyes of the IMP camera are separated by {{Convert|15|cm|inch|abbr=on}} to provide stereoscopic vision and ranging performance to support rover operations. The dual optical paths are folded by two sets of mirrors to bring the light to a single [[charge-coupled device]] (CCD). To minimize moving parts, the IMP is electronically shuttered; half of the CCD is masked and used as a readout zone for the [[electronic shutter]]. The optics had an effective pixel resolution of one milliradian per pixel which gives {{Convert|1|mm|inch|abbr=on}} per pixel at a range of {{Convert|1|m|ft|spell=in|abbr=out|sp=us}}. The camera cylinder is mounted on gimbals that provide rotation freedom of 360° in azimuth and −67° to +90° in elevation. This assembly is supported by an extendible mast that was designed and built by [[AEC Able Engineering]]. The mast holds the camera at approximately {{Convert|1.5|meter|feet|abbr=on}} above the Martian surface and extends ''Pathfinder''{{'}}s horizon to {{Convert|3.4|km|miles|abbr=on}} on a featureless plane.<ref name="NASA" /><ref name=howimpworks>{{cite web |title=How does the IMP works? |url=https://mars.nasa.gov/MPF/imp/howdoes/how_does.html |website=mars.nasa.gov |publisher=NASA |access-date=25 August 2021 |archive-date=5 April 2021 |archive-url=https://web.archive.org/web/20210405121342/https://mars.nasa.gov/MPF/imp/howdoes/how_does.html |url-status=live }}</ref><ref>{{cite journal |last1=Smith |first1=P. H. |title=The imager for Mars Pathfinder experiment |journal=Journal of Geophysical Research |date=February 25, 1997 |volume=102 |issue=2 |pages=4003–4025 |doi=10.1029/96JE03568 |bibcode=1997JGR...102.4003S |doi-access=free }}</ref>

=== Power system ===
[[File:Solar battery of the Sojourner rover.jpg|thumb|Solar panels of the spare rover, ''Marie Curie''. See also [[:File:Battery of the Sojourner rover.jpg|batteries installed on the rover]].]]
''Sojourner'' had solar panels and a non-rechargeable [[Thionyl chloride#Batteries|lithium-thionyl chloride]] (LiSOCl2) battery that could provide 150 [[watt-hour]]s and allowed limited nocturnal operations. Once the batteries were depleted, the rover could only operate during the day.<ref name="faq" /><ref name=soj>{{cite web|url=https://mars.nasa.gov/MPF/rover/descrip.html|title=Description of the Rover Sojourner|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2020-09-19|archive-url=https://web.archive.org/web/20200919093036/https://mars.nasa.gov/MPF/rover/descrip.html|url-status=live}}</ref> The batteries also allowed the rover's health to be checked while enclosed in the cruise stage while ''en route'' to Mars.<ref name=power>{{cite web|url=https://mars.nasa.gov/MPF/roverpwr/power.html|title=Mars Pathfinder Microrover|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2020-10-26|archive-url=https://web.archive.org/web/20201026001215/https://mars.nasa.gov/MPF/roverpwr/power.html|url-status=live}}</ref> The rover had {{Convert|0.22|m2|sqft|abbr=on}} of solar cells, which could produce a maximum of about 15&nbsp;watts on Mars, depending on conditions.<ref name="soj" /> The cells were GaAs/Ge ([[Gallium arsenide germanium solar cell|Gallium Arsenide/Germanium]]) with approximately 18 percent efficiency. They could survive temperatures down to about {{cvt|−140|C|F}}.<ref name="power" /> After about its 40th sol on Mars, the lander's battery no longer held a charge so it was decided to shut off the rover before sunset and wake it up at sunrise.<ref name='Fact check' />

=== Locomotion system ===
[[File:Sojourner side view.gif|thumb|Side view]]
[[File:Sojourner in cruise configuration.gif|thumb|Rover in the cruise configuration]]

The rover's wheels were made of [[aluminum]] and were {{Convert|13|cm|inch|abbr=on}} in diameter and {{Convert|7.9|cm|inch|abbr=on}} wide. They had serrated, [[stainless steel]] tracks that could generate a pressure of {{cvt|1.65|kPa|psi}} in optimal conditions on soft ground.<ref name=Bickler>{{cite book|title=The Mars Rover Mobility System |last=Bickler |first=D. |year=1997 |editor=JPL, NASA |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18908/1/98-0011.pdf |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100526143429/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18908/1/98-0011.pdf |archive-date = 26 May 2010}}</ref> No such need arose during the operational phase.<ref name="Bickler" /> Each wheel was driven by its own independent motor.<ref name=Matijevic2>{{cite journal |title=Sojourner The Mars Pathfinder Microrover Flight Experiment |last=Matijevic |first=J. |author-link=Jacob Matijevic |year=1997 |journal=NASA |hdl=2014/21704 |url=http://hdl.handle.net/2014/21704 |access-date=2 October 2010 |archive-date=13 September 2021 |archive-url=https://web.archive.org/web/20210913081612/https://trs.jpl.nasa.gov/handle/2014/21704 |url-status=live }}</ref> The first and third wheels were used for steering. A six-wheel-steering configuration was considered, but this was too heavy.<ref name="Bickler" /> As the rover rotated on itself, it drew a {{Convert|74|cm|inch|abbr=on|adj=on}} wide circle.<ref name="Matijevic2" />

The wheels were connected to the frame through specially developed suspension to ensure all six were in contact with the ground, even on rough terrain.<ref name="Bickler" /><ref name=Lindemann>{{cite journal|title=Mars Exploration Rover Mobility Assembly Design, Test and Performance |first=R.A. |last=Lindemann | author2=C.J. Voorhees |location=Pasadena, CA |editor=Jet Propulsion Laboratory, National Aeronautics and Space Administration |year=2005 |journal=2005 International Conference on Systems, Man, and Cybernetics, Hawaii, October 10–12, 2005 |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37604/1/05-1950.pdf |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100526124036/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/37604/1/05-1950.pdf | archive-date=26 May 2010 }}</ref> JPL's Don Bickler developed the wheels, which were referred to as "[[Rocker-bogie]]", for the experimental "Rocky" vehicles, of which the ''Sojourner'' is the eighth version.<ref name=Morgan>{{cite web |last=Morgan |first=M. | author2=D. Bickler |year=2000 |title=The retelling of "Romancing the rover (how Sojourner came to be in the late 1980s and its journey to Mars)" |website=JPL |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/36823/1/01-1400.pdf |access-date=25 September 2010 |url-status=dead |archive-url=https://web.archive.org/web/20100527035548/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/36823/1/01-1400.pdf | archive-date=27 May 2010 }}</ref><ref>{{cite patent
 |country=US |number=4840394
 |title=Articulated suspension system|inventor=Donald B. Bickler|pubdate=1988-04-21|gdate=1989-06-20|assign1=NASA
}}</ref><ref>{{cite magazine
 |url=http://www.memagazine.org/backissues/membersonly/april98/features/mars/mars.html
 |last=Bickler |first= Donald |title=Roving over Mars |magazine=Mechanical Engineering |date=April 1998 |pages=74–77
 |archive-url=https://web.archive.org/web/20081022180558/http://www.memagazine.org/backissues/membersonly/april98/features/mars/mars.html
 |archive-date=2008-10-22
}}</ref> They consisted of two elements; "Bogie" connected the front wheel with the central one and "Rocker" connected the rear wheel with the other two. The system did not include springs or other elastic elements, which could have increased the pressure exerted by each wheel.<ref name="Bickler" /> This system allowed the overcoming of obstacles up to {{Convert|8|cm|inch|abbr=on}} high<ref name="dimensions" /> but theoretically would have allowed the rover to overcome obstacles of {{Convert|20|cm|inch|abbr=on}}, or about 30% of the rover's length.<ref name="Bickler" /> The suspension system was also given the ability to collapse on itself so the rover would occupy {{Convert|18|cm|inch|abbr=on}} in the cruising configuration.<ref name=Young214>{{cite book |first=A. |last=Young |title=Lunar and planetary rovers: the wheels of Apollo and the quest for Mars 2007 |year=2007 |editor=Springer |isbn=978-0-387-30774-9 |url=https://books.google.com/books?id=tH930PoDM2UC |pages=212–223 |publisher=Springer |access-date=26 February 2011 |archive-date=13 September 2021 |archive-url=https://web.archive.org/web/20210913081610/https://books.google.com/books?id=tH930PoDM2UC |url-status=live }}</ref>

The locomotion system was found to be suitable for the environment of Mars—being very stable, and allowing forward and backward movements with similar ease<ref name="dimensions" />—and was adopted with appropriate precautions in the subsequent ''[[Spirit (rover)|Spirit]]'' and ''[[Opportunity (rover)|Opportunity]]'' rover missions.<ref name="Lindemann" />

In the ten-year development phase that led to the realization of ''Sojourner'', alternative solutions that could take advantage of the long experience gained at JPL in the development of vehicles for the Moon and Mars were examined.<ref name="Morgan" /> The use of four or more legs was excluded for three reasons: a low number of legs would limit the rover's movements and the freedom of action, and increasing the number would lead to a significant increase in complexity. Proceeding in this configuration would also require knowledge of the space in front—the ground corresponding to the next step—leading to further difficulties.<ref name="Lindemann" /> The choice of a wheeled vehicle solved most of the stability problems, led to a reduction in weight, and improved efficiency and control compared to the previous solution.<ref name="Lindemann" /> The simplest configuration was a four-wheel system that, however, encounters difficulties in overcoming obstacles. Better solutions were the use of six or eight wheels with the rear ones able to push, allowing the obstacle to be overcome. The lighter, simpler, six-wheeled option was preferred.<ref name="Lindemann" />

The rover could travel {{Convert|500|m|ft|abbr=on}} from the lander—the approximate limit of its communication range—<ref name="washington" /> and had a maximum speed of {{Convert|1|cm/s|abbr=on}}.<ref name="dimensions" />

=== Hardware and software ===
[[File:JPL-26575BC.jpg|thumb|Power board (bottom side) and CPU board (top side)]]

''Sojourner'''s [[central processing unit]] (CPU) was an [[Intel 80C85]] with a 2&nbsp;MHz clock, addressing 64 kilobytes (Kb) of memory, and running a [[cyclic executive]].<ref name="ieeecomputer">{{cite journal |first1=Max |last1=Bajracharya |first2=Mark W. |last2=Maimone |first3=Daniel |last3=Helmick |title=Autonomy for Mars rovers: past, present, and future |journal=[[Computer (journal)|Computer]] |publisher=[[IEEE Computer Society]] |date=December 2008 |volume=41 |number=12 |pages=44–50 |doi=10.1109/MC.2008.479 |s2cid=9666797 |issn=0018-9162 |url=http://users.etown.edu/w/wunderjt/ITALY_2009/PUBLICATION_MARS_SPIRIT_ALL_PATH_PLANNING_JPL.pdf |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20160304095252/http://users.etown.edu/w/wunderjt/ITALY_2009/PUBLICATION_MARS_SPIRIT_ALL_PATH_PLANNING_JPL.pdf |archive-date=March 4, 2016 |url-status=live }}</ref> It had four memory stores; 64 Kb of RAM made by IBM for the main processor, 16 Kb of radiation-hardened PROM made by Harris, 176 Kb of non-volatile storage made by Seeq Technology, and 512 Kb of temporary data storage made by Micron. The electronics were housed inside the rover's warm electronics box (WEB).<ref name=faq>{{cite web|url=https://mars.nasa.gov/MPF/rover/faqs_sojourner.html|title=Mars Pathfinder FAQs – Sojourner|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2020-05-24|archive-url=https://web.archive.org/web/20200524212836/https://mars.nasa.gov/MPF/rover/faqs_sojourner.html|url-status=live}}</ref> The WEB is a box-like structure formed from [[fiberglass]] facesheets bonded to aluminum spars. The gaps between facesheets were filled with blocks of [[aerogel]] that worked as [[thermal insulation]].<ref name=Stone1996>{{cite report |title=Mars Pathfinder Microrover: A Small, Low-Cost, Low-Power Spacecraft |last1=Stone |first1=H. W. |year=1996 |url=http://hdl.handle.net/2014/25424 |hdl=2014/25424 |access-date=2021-08-14 |archive-date= 2021-09-13 |archive-url=https://web.archive.org/web/20210913081612/https://trs.jpl.nasa.gov/handle/2014/25424 |url-status=live |publisher=Jet Propulsion Laboratory }}</ref> The aerogel used on the ''Sojourner'' had a density of approximately 20&nbsp;mg/cc.<ref>{{cite web |title=Rover Thermal Design |url=https://mars.nasa.gov/MPF/rover/thermal.html |website=mars.nasa.gov |publisher=NASA |access-date=14 August 2021 |archive-date=14 August 2021 |archive-url=https://web.archive.org/web/20210814195559/https://mars.nasa.gov/MPF/rover/thermal.html |url-status=live }}</ref> This insulator was designed to trap heat generated by rover's electronics; this trapped heat soaked at night through the passive insulation maintaining the electronics in the WEB at between {{Convert|-40|and|40|C|F|abbr=on}}, while externally the rover experienced a temperature range between {{Convert|0|and|-110|C|F|abbr=on}}.<ref name="faq" />

The ''Pathfinder'' lander's computer was a [[IBM RAD6000|Radiation Hardened IBM Risc 6000]] Single Chip with a Rad6000 SC CPU, 128&nbsp;megabytes (Mb) of RAM and 6&nbsp;Mb of [[EEPROM]] memory,<ref>{{cite web | url=http://quest.arc.nasa.gov/mars/ask/about-mars-path/pathfinder_computer.txt | title="QUESTION: What type of computer is the Pathfinder utilizing? ..." (NASA Quest Q&A) | date=1997 | access-date=July 21, 2015 | publisher=[[NASA]] | archive-url=https://web.archive.org/web/20160307043527/http://quest.arc.nasa.gov/mars/ask/about-mars-path/pathfinder_computer.txt | archive-date=March 7, 2016 | url-status=dead }}</ref><ref>{{cite web | url=http://quest.arc.nasa.gov/mars/ask/about-rover/Why_to_use_a_80C85_microprocessor_in_Rover_.txt | title="QUESTION: When it was designed, why was only a single 80C85 CPU used? ..." (NASA Quest Q&A) | date=1997 | access-date=July 21, 2015 | publisher=[[NASA]] | archive-url=https://web.archive.org/web/20150723003545/http://quest.arc.nasa.gov/mars/ask/about-rover/Why_to_use_a_80C85_microprocessor_in_Rover_.txt | archive-date=July 23, 2015 | url-status=dead }}</ref> and its [[operating system]] was [[VxWorks]].<ref name=Wind_River>{{cite web | url=http://www.windriver.com/news/press/pr.html?ID=314 | title=Wind River Powers Mars Exploration Rovers—Continues Legacy as Technology Provider for NASA's Space Exploration | date=June 6, 2003 | access-date=August 28, 2009 | publisher=[[Wind River Systems]] | archive-url=https://web.archive.org/web/20100106090354/http://www.windriver.com/news/press/pr.html?ID=314 | archive-date=January 6, 2010 | url-status=live }}</ref>

The mission was jeopardised by a [[Concurrent computing|concurrent]] software bug in the lander<ref>Parallel sparking: Many chips make light work, Douglas Heaven, ''New Scientist'' magazine, issue 2930, August 19, 2013, p44. [https://www.newscientist.com/article/mg21929301.000-parallel-sparking-many-chips-make-light-work.html?page=2 Online (by subscription)] {{Webarchive|url=https://web.archive.org/web/20141006101728/http://www.newscientist.com/article/mg21929301.000-parallel-sparking-many-chips-make-light-work.html?page=2 |date=October 6, 2014 }}</ref> that had been found in preflight testing but was deemed a glitch and given a low priority because it only occurred in certain unanticipated heavy-load conditions, and the focus was on verifying the entry and landing code. The problem, which was reproduced and corrected from Earth using a laboratory duplicate, was due to [[Reset (computing)|computer resets]] caused by [[priority inversion]]. No scientific or engineering data was lost after a computer reset but all of the following operations were interrupted until the next day.<ref>{{cite web |url=http://research.microsoft.com/en-us/um/people/mbj/Mars_Pathfinder/Authoritative_Account.html |title=What really happened on Mars? – Authoritative Account |first=Glenn E. |last=Reeves |work=Microsoft.com |date=December 15, 1997 |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20150611035733/http://research.microsoft.com/en-us/um/people/mbj/mars_pathfinder/authoritative_account.html |archive-date=June 11, 2015 |url-status=live }}</ref><ref>{{cite web |url=http://research.microsoft.com/en-us/um/people/mbj/Mars_Pathfinder/ |title=What really happened on Mars? |first=Michael B. |last=Jones |work=Microsoft.com |date=December 16, 1997 |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20150612010836/http://research.microsoft.com/en-us/um/people/mbj/mars_pathfinder/ |archive-date=June 12, 2015 |url-status=live }}</ref> Resets occurred on July 5, 10, 11 and 14 during the mission<ref>{{cite web|url= http://www.oarval.org/missionsr2.htm|title= The Mars Pathfinder Mission Status Reports — Second Week|publisher= Office of the Flight Operations Manager – Mars Pathfinder Project|access-date= October 24, 2015|archive-url= https://web.archive.org/web/20160104210211/http://www.oarval.org/missionsr2.htm|archive-date= January 4, 2016|url-status= live}}</ref> before the software was patched on July 21 to enable [[priority inheritance]].<ref>{{cite web|url= http://www.oarval.org/missionsr3.htm|title= The Mars Pathfinder Mission Status Reports — Third Week|publisher= Office of the Flight Operations Manager – Mars Pathfinder Project|access-date= October 24, 2015|archive-url= https://web.archive.org/web/20160410091935/http://www.oarval.org/missionsr3.htm|archive-date= April 10, 2016|url-status= live}}</ref>

=== Communication and cameras ===
''Sojourner'' communicated with its base station using a 9,600 [[baud]] radio modem, although error-checking protocols limited communications to a functional rate of 2,400 baud with a theoretical range of about {{Convert|1/2|km|mile|abbr=out|spell=in}}. Under normal operation, it would periodically send a "[[Heartbeat (computing)|heartbeat]]" message to the lander. If no response was given, the rover could autonomously return to the location at which the last heartbeat was received. If desired, the same strategy could be used to deliberately extend the rover's operational range beyond that of its radio transceiver, although the rover rarely traveled further than {{Convert|10|meter|ft|abbr=out}} from ''Pathfinder'' during its mission.<ref name="faq" /> The [[Ultra high frequency]] (UHF) radio modems operated in [[half duplex|half-duplex]] mode, meaning they could either send or receive data but not both at the same time. The data was communicated in bursts of 2&nbsp;kB.<ref name="radio">{{cite web|url=https://mars.nasa.gov/MPF/rovercom/itworks.html|title=How the Mars Microrover Radios and Antennas Work|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2021-04-17|archive-url=https://web.archive.org/web/20210417174513/https://mars.nasa.gov/MPF/rovercom/itworks.html|url-status=live}}</ref>

The rover was imaged on Mars by the base station's IMP camera system, which also helped determine where the rover should go.<ref name="roll" />
The rover had two monochrome cameras in front and a color camera at the rear. Each front camera had an array 484 pixels high by 768 wide. The cameras used CCDs manufactured by [[Eastman Kodak Company]]; they were clocked out by CPU, and capable of [[auto-exposure]], [[Block Truncation Coding]] (BTC) [[data compression]], bad pixel/column handling, and image data packetizing.<ref name="ins"/>

[[File:Pixel map of Sojourner color camera.jpg|thumb|150px|Pixel map of the color camera]]

Both front cameras were coupled with five [[laser]] stripe projectors that enabled [[stereoscopy|stereoscopic]] images to be taken along with measurements for hazard detection in the rover's path. The optics consisted of a window, lens, and [[Field flattener lens|field flattener]]. The window was made of [[Sapphire#Applications|sapphire]] while the lens objective and flattener were made of [[zinc selenide]].<ref name="ins"/>

Another color camera was located on the back of the rover near the APXS, and rotated by 90°. It provided images of the APXS's target area and the rover's ground tracks.<ref name="ins"/>

The sensor of this color camera was arranged so 12 of 16 pixels of a 4×4 pixel block were sensitive to green light; while 2 pixels were sensitive to red light and the other 2 were sensitive to [[infrared]] and blue light.<ref name="ins"/>

Because the rover's cameras had zinc-selenide lenses, which block light with a [[Light|wavelength]] shorter than 500&nbsp;nanometers (nm), no blue light actually reached the blue-and-infrared-sensitive pixels, which therefore recorded only infrared light.<ref name="ins">{{cite web|url=http://pdsimage.wr.usgs.gov/data/mpfr-m-apxs-2-edr-v1.0/mprv_0001/document/rcinst.htm|title=Rover Camera Instrument Description|access-date=2014-03-09|archive-date=2017-01-18|archive-url=https://web.archive.org/web/20170118022602/http://pdsimage.wr.usgs.gov/data/mpfr-m-apxs-2-edr-v1.0/mprv_0001/document/rcinst.htm|url-status=live}}</ref>

=== Rover Control Software ===
''Sojourner'' operation was supported by "Rover Control Software" (RCS) that ran on a [[SGI Onyx2|Silicon Graphics Onyx2]] computer on Earth and allowed command sequences to be generated using a graphical interface. The rover driver would wear 3D goggles supplied with imagery from the base station and would move a virtual model with a specialized joystick. The control software allowed the rover and surrounding terrain to be viewed from any angle, supporting the study of terrain features, the placing of waypoints, and virtual flyovers. Darts were used as icons to show where the rover should go. Desired locations were added to a sequence and sent to the rover to perform. Typically, a long sequence of commands were composed and sent once a day.<ref name=mfex>{{cite web|url=https://mars.nasa.gov/MPF/roverctrlnav/rcw.html|title=MFEX: Microrover Flight Experiment – Rover Control Workstation|last=Cooper|first=Brian K.|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2021-08-14|archive-url=https://web.archive.org/web/20210814200418/https://mars.nasa.gov/MPF/roverctrlnav/rcw.html|url-status=live}}</ref><ref>{{cite web |last1=Mishkin |first1=Andrew |title=Making Tracks on Mars Mission Operations for Deep Space |url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38751/1/06-0058.pdf |website=trs-new.jpl.nasa.gov |publisher=NASA, JPL |archive-url=https://web.archive.org/web/20120323160409/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38751/1/06-0058.pdf |access-date=17 August 2021|archive-date=2012-03-23 }}</ref> The rover drivers were Brian K. Cooper and Jack Morrison.<ref name="Sojourner" />

<gallery mode="packed">
File:Sojourner visualization software 1.jpg|Example of a screen that visualized the surface of Mars, used by rover driver
File:Sojourner visualization software 2.jpg|Example of "virtual reality" interface that allowed driver to see the surface from any angle around the rover
File:Brian K. Cooper, primary Sojourner rover driver.jpg|Brian K. Cooper, primary rover driver, with a pair of stereo goggles
File:Sojourner rover driver in 3D goggles.png|Cooper in stereo goggles working with RCS
</gallery>

== Science payload ==

=== Alpha Proton X-Ray Spectrometer ===
{{Main|Alpha particle X-ray spectrometer}}

The Alpha Proton X-Ray [[Spectrometer]] (APXS) was designed to determine the [[chemical composition]] of [[Martian soil]], rocks and dust by analyzing the return radiation in its alpha, proton, and X-ray components resulting from the sample's exposure to a radioactive source contained in the instrument.<ref name=APXSrieder>{{cite journal |title=Determination of the chemical composition of Martian soil and rocks:The alpha proton X ray spectrometer | author= R. Rieder | author2=H. Wänke| author3= T. Economou| author4= A. Turkevich |journal= Journal of Geophysical Research: Planets|year=1997 |volume=102 | issue= E2 |pages=4027–4044 |doi=10.1029/96JE03918| bibcode= 1997JGR...102.4027R |doi-access=free }}</ref><ref name=APXSjpl>{{cite web |title=Mars Pathfinder Instrument Descriptions |editor=JPL, NASA |url=http://marsprogram.jpl.nasa.gov/MPF/mpf/sci_desc.html |access-date=3 October 2010 |archive-date=4 June 2011 |archive-url=https://web.archive.org/web/20110604055857/http://marsprogram.jpl.nasa.gov/MPF/mpf/sci_desc.html |url-status=live }}</ref> The instrument had a [[curium]]-244 source<ref name="Wanke" /> that emits [[alpha particle]]s with an energy of 5.8 MeV and a half-life of 18.1 years. A portion of the incident radiation that impacted the analyzed sample's surface was reflected and the remainder interacted with the sample.<ref name="NASA" />

The principle of the APXS technique is based on the interaction of alpha particles from a [[radioisotope]] source with matter. There are three components of the return radiation; simple [[Rutherford backscattering]], production of protons from reactions with the nucleus of light elements, and generation of [[X-ray]]s upon recombination of atomic shell vacancies created by alpha particle bombardment by interaction with the electrons of the innermost orbitals.<ref name="NASA">{{cite web |last1=Smith |first1=Peter H. |title=Mars Pathfinder PIP (Continued – Part 2/3) |url=https://science.ksc.nasa.gov/mirrors/jpl/pathfinder/nasa/pippt2.html |website=science.ksc.nasa.gov |access-date=20 August 2021 |archive-url=https://web.archive.org/web/20210820144438/https://science.ksc.nasa.gov/mirrors/jpl/pathfinder/nasa/pippt2.html |archive-date=20 August 2021 |url-status=live}} {{PD-notice}}</ref> The instrument was designed to detect the energy of all three components of the return radiation, making it possible to identify the atoms present and their quantities in a few tens of micrometers below the surface of the analyzed sample.<ref name=RiederAPXS>{{cite journal |title=The Chemical Composition of Martian Soil and Rocks Returned by the Mobile Alpha Proton X-ray Spectrometer: Preliminary Results from the X-ray Mode |first=R. |last=Rieder |journal=Science |year=1997 |volume=278 |number=5344 |pages=1771–1774 |doi=10.1126/science.278.5344.1771 |pmid=9388173 |bibcode=1997Sci...278.1771R |doi-access=free }}</ref> The detection process was rather slow; each measurement could take up to ten hours.<ref name=Blomquist>{{cite journal |title=The Alpha-Proton-X-ray Spectrometer Deployment Mechanism – An Anthropomorphic Approach to Sensor Placement on Martian Rocks and Soil |last=Blomquist |first=R.S. |url=http://hdl.handle.net/2014/33265 |journal=29th Aerospace Mechanisms Symposium. NASA Johnson Space Center. 1995 |year=1995 |page=61 |bibcode=1995aeme.symp...61B |hdl=2014/33265 |access-date=11 October 2010 |archive-date=13 September 2021 |archive-url=https://web.archive.org/web/20210913081613/https://trs.jpl.nasa.gov/handle/2014/33265 |url-status=live }}</ref>

Sensitivity and selectivity depends on a channel; alpha backscattering has high sensitivity for light elements like [[carbon]] and [[oxygen]], [[proton emission]] is mainly sensitive to [[sodium]], [[magnesium]], [[aluminium]], [[silicon]], [[sulfur]], and [[X-ray emission]] is more sensitive to heavier elements [[sodium]] to [[iron]] and beyond. Combining all three measurements makes APXS sensitive to all elements with the exception of [[hydrogen]] that is present at concentration levels above a fraction of one percent.<ref name="NASA" /> The instrument was designed for the failed Russian [[Mars-96]] mission.<ref name=Wanke>{{cite journal |title=Chemical Composition of Rocks and Soils at the Pathfinder Site |first=H. |last=Wänke | author2=J. Brückner| author3= G. Dreibus| author4= R. Rieder| author5= I. Ryabchikov |journal=Space Science Reviews |volume=96 |pages=317–330 |year=2001 |doi=10.1023/A:1011961725645|bibcode=2001SSRv...96..317W |s2cid=189767835 }}</ref> The alpha particle and proton detectors were provided by the Chemistry Department of the [[Max Planck Institute]] and the X-ray detector was developed by the [[University of Chicago]].<ref name="APXSjpl" />

During each measurement, the front surface of the instrument had to be in contact with the sample.<ref name="APXSjpl" /> For this to be possible, the APXS was mounted on a [[robotic arm]] called the Alpha-Proton-X-ray Spectrometer Deployment Mechanism (ADM). The ADM was an [[anthropomorphic]] actuator that was equipped with a wrist that was capable of rotations of ±25°.<ref name="Blomquist" /> The dual mobility of the rover and the ADM increased the potential of the instrument—the first of its kind to reach Mars.<ref name="Wanke" />

=== Wheel Abrasion Experiment ===
[[File:Mars Pathfinder Wheel Abrasion Experiment.gif|thumb|The wheel affected by the Wheel Abrasion Experiment.]]

The Wheel Abrasion Experiment (WAE) was designed to measure the abrasive action of Martian soil on thin layers of aluminum, nickel, and platinum, and thus deduce the grain size of the soil at the landing site. For this purpose, 15 layers—five of each metal—were mounted on one of the two central wheels with a thickness between 200 and 1000 [[ångström]], and electrically isolated from the rest of the rover. By directing the wheel appropriately, sunlight was reflected towards a nearby [[Photocell|photovoltaic sensor]]. The collected signal was analyzed to determine the desired information.<ref name=Deposits>{{cite journal| author=The Rover Team |title=Characterization of the Martian Surface Deposits by the Mars Pathfinder Rover, Sojourner |journal=Science |year=1997 |volume=278 | number=5344 |pages=1765–1768 |doi=10.1126/science.278.5344.1765|bibcode=1997Sci...278.1765M |doi-access=free }}</ref> For the abrasive action to be significant on the mission schedule, the rover was scheduled to stop at frequent intervals and, with the other five wheels braked, force the WAE wheel to rotate, causing increased wear.<ref name=Ferguson>{{cite journal| author=D.C. Ferguson |title=Evidence for Martian electrostatic charging and abrasive wheel wear from the Wheel Abrasion Experiment on the Pathfinder Sojourner rover |journal=J. Geophys. Res. |volume=104 | number=E4 |pages=8747–8789 |year=1999 |doi=10.1029/98JE02249 |bibcode=1999JGR...104.8747F }}</ref> Following the WAE experiment on Mars, attempts were made to reproduce the effects observed in the laboratory.<ref name="Ferguson" />

The interpretation of the results proposed by Ferguson ''et al''. suggests the soil at the landing site is made up of fine-grained dust of limited hardness with a grain size of less than 40&nbsp;μm.<ref name="Ferguson" /> The instrument was developed, built and directed by the Lewis' Photovoltaics and Space Environments Branch of the [[Glenn Research Center]].<ref name="Ferguson" />

=== Materials Adherence Experiment ===
{{Main|Materials Adherence Experiment}}

The Materials Adherence Experiment (MAE) was designed by engineers at the Glenn Research Center to measure the daily accumulation of dust on the back of the rover and the reduction in the energy-conversion capacity of the photovoltaic panels.<ref name=Stevenson>{{cite book| author=S.M. Stevenson |title=Mars Pathfinder Rover—Lewis Research Center Technology Experiments Program. NASA Technical Memorandum 107449. |year=1997 |editor=NASA |url=http://gltrs.grc.nasa.gov/reports/1997/TM-107449.pdf |access-date=23 October 2010 | url-status=dead |archive-url=https://web.archive.org/web/20061010164758/http://gltrs.grc.nasa.gov/reports/1997/TM-107449.pdf | archive-date=10 October 2006 }}</ref><ref name=Landis>{{cite web |title=Measuring Dust on Mars |first=G.A. |last=Landis |editor=NASA |url=http://www.grc.nasa.gov/WWW/RT/RT1997/5000/5410landis.htm |access-date=23 October 2010 |year=1998 |url-status=dead |archive-url=https://web.archive.org/web/20110911103308/http://www.grc.nasa.gov/WWW/RT/RT1997/5000/5410landis.htm | archive-date=11 September 2011}}</ref> It consisted of two sensors.<ref name="Stevenson" />

The first was composed of a photovoltaic cell covered by transparent glass that could be removed on command. Near local midday, measurements of the cell's energy yield were made, both with the glass in place and removed. From the comparison, it was possible to deduce the reduction in cell yield caused by the dust.<ref name="Stevenson" /> Results from the first cell were compared with those of a second photovoltaic cell that was exposed to the Martian environment.<ref name="Stevenson" /> The second sensor used a quartz crystal microbalance (QCM) to measure the weight-per-surface unit of the dust deposited on the sensor.<ref name="Stevenson" />

During the mission, a daily rate equal to 0.28% of percentage reduction in the energy efficiency of the photovoltaic cells was recorded. This was independent of whether the rover was stationary or in motion.<ref name="Landis" /> This suggests the dust settling on the rover was suspended in the atmosphere and was not raised by the rover's movements.<ref name="Deposits" />

== Control system ==
[[File:Rover movie sol21 S0050N.gif|thumb|''Sojourner'' overcomes a height difference.]]

Since it was established transmissions relating to driving the ''Sojourner'' would occur once every sol, the rover was equipped with a computerized control system to guide its movements independently.<ref name=Matijevic>{{cite journal |title=Autonomous Navigation and the Sojourner Microrover |last=Matijevic |first=J. |author-link=Jacob Matijevic |year=1998 |journal=Science |volume=215 |hdl=2014/19052 |url=http://hdl.handle.net/2014/19052 |access-date=1 October 2010 |archive-date=13 September 2021 |archive-url=https://web.archive.org/web/20210913081613/https://trs.jpl.nasa.gov/handle/2014/19052 |url-status=live }}</ref>

A series of commands had been programmed, providing an appropriate strategy for overcoming obstacles. One of the primary commands was "Go to Waypoint". A local reference system, of which the lander was the origin, was envisaged. Coordinate directions were fixed at the moment of landing, taking the direction of north as a reference. During the communication session (once per sol), the rover received from Earth a command string containing the coordinates of the arrival point, which it would have to reach autonomously.<ref name="Matijevic" />

The algorithm implemented on the on-board computer attempted, as a first option, to reach the obstacle in a straight line from the starting position. Using a system of photographic objectives and laser emitters, the rover could identify obstacles along this path. The on-board computer was programmed to search for the signal produced by the lasers in the cameras' images. In the case of a flat surface and no obstacles, the position of this signal was unchanged with respect to the reference signal stored in the computer; any deviation from this position made it possible to identify the type of obstacle.<ref name="Matijevic" /> The photographic scan was performed after each advance equal to the diameter of the wheels, {{Convert|13|cm|inch|abbr=on}}, and before each turn.<ref name="Matijevic2" />

[[File:PIA04316.jpg|thumb|One of the obstacle detection images taken by ''Sojourner''. The laser trace is clearly visible.]]

In the confirmed presence of an obstacle,{{efn|It was foreseen the possibility that three false positives out of twenty detections carried out before proceeding}} the computer commanded the execution of a first strategy to avoid it. The rover, still by itself, rotated until the obstacle was no longer in sight. Then, after having advanced for half of its length, it recalculated a new straight path that would lead it to the point of arrival. At the end of the procedure, the computer had no memory of the existence of the obstacle.<ref name="Matijevic" /> The steering angle of the wheels was controlled through [[potentiometer]]s.<ref name="Matijevic2" />

In particularly uneven terrain, the procedure described above would have been prevented by the presence of a large number of obstacles. There was, therefore, a second procedure known as "thread the needle", which consisted of proceeding between two obstacles along the [[bisection|bisector]] between them, providing they were sufficiently spaced to allow the rover to pass. If the rover had encountered a clearing before reaching a predetermined distance, it would have had to rotate on itself to calculate a new straight trajectory to reach the target. Conversely, the rover would have had to go back and try a different trajectory. As a last resort, contact sensors were mounted on the front and rear surfaces of the rover.<ref name="Matijevic" />

To facilitate the rover's direction, an appropriate on-the-spot rotation could be commanded from Earth. The command was "Turn" and was performed using a [[gyroscope]].<ref name="Matijevic2" /> Three [[accelerometer]]s measured the acceleration of gravity along three perpendicular directions, making it possible to measure the surface's slope. The rover was programmed to deviate from routes that would require a slope greater than 30°,<ref name="Matijevic" /> though it was designed not to tip over when tilted at 45°.<ref name="Matijevic2" /> The distance traveled was determined by the number of revolutions of the wheels.<ref name="Matijevic" />

== ''Marie Curie'' ==

''Marie Curie'' is a flight spare for the ''Sojourner''. During the operational phase on Mars, the sequences of the most complex commands to be sent to ''Sojourner'' were verified on this identical rover at JPL.<ref>{{cite thesis |title=Theory and Experiments in Autonomous Sensor-Based Motion Planning with Applications for Flight Planetary Microrovers |author=Laubach, S.L. |year=1999 |editor=California Institute of Technology |location=Pasadena, California |page=34 |publisher=California Institute of Technology |doi=10.7907/b1wv-hc78 |url=http://thesis.library.caltech.edu/688/ |access-date=5 June 2011 |archive-date=23 September 2015 |archive-url=https://web.archive.org/web/20150923162442/http://thesis.library.caltech.edu/688/ |type=phd |url-status=live }} [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.38.8801&rep=rep1&type=pdf pdf] {{Webarchive|url=https://web.archive.org/web/20210430160819/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.38.8801&rep=rep1&type=pdf |date=2021-04-30 }}</ref> NASA planned to send ''Marie Curie'' on the canceled [[Mars Surveyor 2001]] mission; it was suggested to send it in 2003, proposing ''Marie Curie'' to be deployed "using a robotic-arm attached to the lander".<ref>{{cite web |last=Mishkin |first=Andrew |author-link=Andrew Mishkin |title= An automated rover command generation prototype for the Mars 2003 Marie Curie rover|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/14471/1/00-0911.pdf |publisher=NASA |archive-url=https://web.archive.org/web/20120323160218/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/14471/1/00-0911.pdf |access-date=17 August 2021|archive-date=2012-03-23 }}</ref> Rather than this, the [[Mars Exploration Rover]] program was launched in 2003. In 2015, JPL transferred ''Marie Curie'' to the [[National Air and Space Museum|Smithsonian National Air and Space Museum]] (NASM).<ref>{{cite web |title=Rover, Marie Curie, Mars Pathfinder, Engineering Test Vehicle |url=https://airandspace.si.edu/collection-objects/rover-marie-curie-mars-pathfinder-engineering-test-vehicle/nasm_A20150317000 |publisher=National Air and Space Museum |access-date=13 August 2021 |archive-date=13 August 2021 |archive-url=https://web.archive.org/web/20210813071724/https://airandspace.si.edu/collection-objects/rover-marie-curie-mars-pathfinder-engineering-test-vehicle/nasm_A20150317000 |url-status=live }}</ref>

According to space historian and NASM curator Matt Shindell:
{{Cquote
| quote = The ''Marie Curie'' rover was a fully operational unit, I’m not sure at what point it was decided which was going to fly and which one would stay home, but it was ready to replace the main unit at a moment’s notice.<ref>{{cite web |last1=Kindy |first1=David |title=Recalling the Thrill of Pathfinder's Mission to Mars |url=https://www.smithsonianmag.com/smithsonian-institution/recalling-thrill-pathfinders-mission-mars-180977008/ |website=smithsonianmag.com |publisher=Smithsonian Magazine |access-date=14 August 2021 |archive-date=14 August 2021 |archive-url=https://web.archive.org/web/20210814193646/https://www.smithsonianmag.com/smithsonian-institution/recalling-thrill-pathfinders-mission-mars-180977008/ |url-status=live }}</ref>
}}
{{-}}

== Mars Yard ==
[[File:JPL Mars Yard.jpg|thumb|upright=1.2|''Sojourner'' at the Mars Yard test area (see also [[:File:Sojourner at JPL Mars Yard 01.jpg|test rover at the Yard]])]]

To test robotic prototypes and applications under natural lighting conditions, JPL built a simulated Martian landscape called "Mars Yard". The test area measured {{Convert|21|by|22|meters|ft|abbr=on}} and had a variety of terrain arrangements to support multiple test conditions. The soil was a combination of beach sand, decomposed granite, brick dust, and volcanic cinders. The rocks were several types of basalts, including fine-grained and vesicular in both red and black. Rock-size distributions were selected to match those seen on Mars and the soil characteristics matched those found in some Martian regions. Large rocks were not Mars-like in composition, being less dense and easier to move for testing. Other obstacles such as bricks and trenches were often used for specialized testing.<ref>{{cite web |title=The MarsYard II |url=https://www-robotics.jpl.nasa.gov/facilities/facility.cfm?Facility=1 |website=www-robotics.jpl.nasa.gov |publisher=NASA, JPL |access-date=21 August 2021 |archive-date=21 August 2021 |archive-url=https://web.archive.org/web/20210821112313/https://www-robotics.jpl.nasa.gov/facilities/facility.cfm?Facility=1 |url-status=live }}{{PD-notice}}</ref> Mars Yard was expanded in 1998 and then in 2007 to support other Mars rover missions.<ref>{{cite web |last1=Kelly |first1=Tiffany |title=JPL engineers test out their rovers on a fake Red Planet |url=https://www.mcall.com/tn-pas-0805-getting-their-mars-yard-work-done-story.html |website=mcall.com |publisher=The Morning Call |access-date=2021-08-21 |archive-date=2021-08-21 |archive-url=https://web.archive.org/web/20210821113901/https://www.mcall.com/tn-pas-0805-getting-their-mars-yard-work-done-story.html |url-status=live }}</ref>

== Naming ==
[[File:SojournerTruth 1850 OliveGilbert.PNG|thumb|[[Sojourner Truth]]]]

The name "Sojourner" was chosen for the rover through a competition held in March 1994 by the [[Planetary Society]] in collaboration with JPL; it ran for one year and was open to students of 18 years and below from any country. Participants were invited to choose a "heroine to whom to dedicate the rover" and to write an essay about her accomplishments, and how these accomplishments could be applied to the Martian environment.<ref name=Name>{{cite web |url=http://mars.jpl.nasa.gov/MPF/rover/name.html |title=NASA Names First Rover to Explore the Surface of Mars |editor=NASA |access-date=24 September 2010 |archive-date=7 June 2011 |archive-url=https://web.archive.org/web/20110607010535/http://mars.jpl.nasa.gov/MPF/rover/name.html |url-status=live }}</ref> The initiative was publicized in the United States through the January 1995 edition of the magazine ''[[Science and Children]]'' published by the [[National Science Teachers Association]].<ref name="Name" />

Some 3,500 papers were received from countries including Canada, India, Israel, Japan, Mexico, Poland, Russia, and the United States, of which 1,700 were from students aged between 5 and 18. The winners were chosen on the basis of the quality and creativity of the work, the appropriateness of the name for a Martian rover, and the competitor's knowledge of the heroine and the probe mission.<ref name="Name" /> The winning paper was written by 12-year-old Valerie Ambroise of Bridgeport, Connecticut, who suggested dedicating the rover to [[Sojourner Truth]],<ref>{{Cite news|url=https://www.nytimes.com/1997/07/14/nyregion/girl-who-named-mars-rover-stays-down-to-earth.html|title=Girl Who Named Mars Rover Stays Down to Earth|date=1997-07-14|work=The New York Times|access-date=2019-01-24|language=en-US|issn=0362-4331|archive-date=2020-10-26|archive-url=https://web.archive.org/web/20201026001112/https://www.nytimes.com/1997/07/14/nyregion/girl-who-named-mars-rover-stays-down-to-earth.html|url-status=live}}</ref> a [[American Civil War|Civil War era]] African-American [[abolitionist]] and women's rights advocate.<ref name="Name" /> The second place went to Deepti Rohatgi, 18, of [[Rockville, Maryland]], who proposed [[Marie Curie]], a Nobel Prize-winning Franco-Polish chemist. Third place went to Adam Sheedy, 16, of Round Rock, Texas, who chose [[Judith Resnik]], a United States astronaut and [[Space Shuttle]] crew member who died in the [[Space Shuttle Challenger disaster|1986 ''Challenger'' disaster]].<ref name="Name" /> The rover was also known as ''Microrover Flight Experiment'' abbreviated MFEX.<ref name="roll">{{cite web|url=https://mars.nasa.gov/MPF/martianchronicle/martianchron7/microrover.html|title=Mars Pathfinder Microrover Ready to Roll!|website=mars.nasa.gov|access-date=2021-08-15|archive-date=2019-12-02|archive-url=https://web.archive.org/web/20191202124258/https://mars.jpl.nasa.gov/MPF/martianchronicle/martianchron7/microrover.html|url-status=live}}</ref>

== Operations ==
[[File:Mars Pathfinder opens after landing.gif|thumb|Position of the rover on the lander after opening of the petals.]]

''Sojourner'' was launched on December 4, 1996, aboard a [[Delta II]] booster, and reached Mars on July 4, 1997. It operated in [[Ares Vallis]] channel in the [[Chryse Planitia]] of the [[Oxia Palus quadrangle]],<ref name=MEP>{{cite web |url=http://mpfwww.jpl.nasa.gov/missions/past/pathfinder.html |title=Mars Pathfinder |website=Mars Exploration Program |editor=NASA |access-date=23 November 2010 |url-status=dead |archive-url=https://web.archive.org/web/20050413001059/http://mpfwww.jpl.nasa.gov/missions/past/pathfinder.html | archive-date=13 April 2005}}</ref> from July 5<ref name=Operations>{{cite web |url=http://marsprogram.jpl.nasa.gov/MPF/ops/rover.html |title=Summary of Rover Operations |website=Mars Pathfinder Mission |editor=JPL, NASA |access-date=24 September 2010 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025083109/http://marsprogram.jpl.nasa.gov/MPF/ops/rover.html |url-status=live }}</ref> to September 27, 1997, when the lander cut off communications with Earth.<ref name="MEP" /> In the 83 sols of activity—twelve times the expected duration for the rover—''Sojourner'' traveled {{Convert|104|meters|ft|abbr=on}}, always remaining within {{Convert|12|meters|ft|abbr=on}} of the lander.<ref name="Wanke" /> It collected 550 images,<ref name="MEP" /> performed 16 analyzes through the APXS—nine of rocks and the remainder of the soil—<ref name="Wanke" /> and performed 11 Wheel Abrasion Experiments and 14 experiments on soil mechanics in cooperation with the lander.<ref name="Matijevic2" /><ref>{{cite web |url=http://marsprogram.jpl.nasa.gov/MPF/roversci/site-map-menu.html |title=Summary of Rover Activity |publisher=NASA |access-date=23 November 2010 |archive-date=25 October 2011 |archive-url=https://web.archive.org/web/20111025170545/http://marsprogram.jpl.nasa.gov/MPF/roversci/site-map-menu.html |url-status=live }}</ref>

=== Landing site ===
The landing site for the rover was chosen in April 1994 at the [[Lunar and Planetary Institute]] in Houston. The landing site is an ancient flood plain called [[Ares Vallis]], which is located in Mars' northern hemisphere and is one of the rockiest parts of Mars. It was chosen because it was thought to be a relatively safe surface on which to land and one that contains a wide variety of rocks that were deposited during a flood. This area was well-known, having been photographed by the ''[[Viking program|Viking]]'' mission.<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><ref>{{cite web |title=Mars Pathfinder Landing Site |url=https://www.lpi.usra.edu/publications/slidesets/marslife/slide_36.html |website=lpi.usra.edu |publisher=Lunar and Planetary Institute |access-date=17 August 2021 |archive-date=2 August 2010 |archive-url=https://web.archive.org/web/20100802074854/http://www.lpi.usra.edu/publications/slidesets/marslife/slide_36.html |url-status=live }}</ref><ref>{{cite web |title=Mars Pathfinder Landing Site |url=https://nssdc.gsfc.nasa.gov/planetary/marsland.html |website=nssdc.gsfc.nasa.gov |publisher=NASA |access-date=17 August 2021 |archive-date=23 April 2021 |archive-url=https://web.archive.org/web/20210423165309/https://nssdc.gsfc.nasa.gov/planetary/marsland.html |url-status=live }}</ref> After a successful landing, the lander was officially named "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>

=== Deployment ===
{{See also|Mars Pathfinder#Entry, descent and landing}}

''Mars Pathfinder'' landed on July 4, 1997. The petals were deployed 87 minutes later with ''Sojourner'' rover and the solar panels attached on the inside. The rover exited the lander on the next day.<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=February 16, 2021 |website=nssdc.gsfc.nasa.gov |archive-date=January 27, 2021 |archive-url=https://web.archive.org/web/20210127200641/https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1996-068A |url-status=live }}</ref>

=== Rock analysis ===
[[File:PIA01151.jpg|thumb|Overhead view of the area surrounding the lander illustrating the rover traverse. Red rectangles are rover positions at the end of sols 1–30. Locations of soil mechanics and wheel abrasion experiments, and APXS measurements are shown.]]

The rocks at the landing site were given names of cartoon characters. Among them were Pop Tart, Ender, mini-Matterhorn, Wedge, Baker's Bench, Scooby Doo, Yogi, Barnacle Bill, Pooh Bear, Piglet, the Lamb, the Shark, Ginger, Souffle, Casper, Moe, and Stimpy. A dune was called Mermaid Dune, and a pair of hills were named Twin Peaks.<ref>{{cite web |title=Mars Pathfinder Black and White Images |url=https://nssdc.gsfc.nasa.gov/planetary/marspath_images_bw.html |website=nssdc.gsfc.nasa.gov |publisher=NASA |access-date=16 August 2021 |archive-date=16 August 2021 |archive-url=https://web.archive.org/web/20210816114636/https://nssdc.gsfc.nasa.gov/planetary/marspath_images_bw.html |url-status=live }}</ref><ref>{{cite web |title=Rocks explored by the Rover |url=https://www.windows2universe.org/mars/exploring/MPF_rocks.html |website=windows2universe.org |publisher=Windows to the Universe |access-date=16 August 2021 |archive-date=16 August 2021 |archive-url=https://web.archive.org/web/20210816114638/https://www.windows2universe.org/mars/exploring/MPF_rocks.html |url-status=live }}</ref><ref name=geology>{{cite web |title=Mars Pathfinder Science Results: Geology |url=https://mars.nasa.gov/MPF/science/geology.html |website=mars.nasa.gov |publisher=NASA |access-date=16 August 2021 |archive-date=20 March 2021 |archive-url=https://web.archive.org/web/20210320060048/https://mars.nasa.gov/MPF/science/geology.html |url-status=live }}</ref>

The first analysis was carried out on the rock called "[[Barnacle Bill (Martian rock)|Barnacle Bill]]" during the third sol. The rock's composition was determined by the APXS spectrometer, which took 10 hours for a complete scan. The rock "[[Yogi Rock|Yogi]]" was analyzed on the 10th sol.<ref name="Operations" /><ref>{{cite news |title='Yogi' Rock Found On Mars Similar To Rocks Underneath 'Yogi' Berra Stadium, Geologist Says |journal=ScienceDaily |year=1997 |author=Montclair State University |url=http://www.sciencedaily.com/releases/1997/08/970813214200.htm |access-date=7 June 2011 |archive-date=4 June 2011 |archive-url=https://web.archive.org/web/20110604233433/http://www.sciencedaily.com/releases/1997/08/970813214200.htm |url-status=live }}</ref> It has been suggested the conformation of the land close to the rock, even visually at a lower level than the surrounding surface, was derived from the evaporation of floodwater.<ref>{{cite web |title=Yogi Rock |website=[[Astronomy Picture of the Day]] |editor=NASA |date=11 July 1997 |url=http://apod.nasa.gov/apod/ap970711.html |access-date=7 June 2011 |archive-date=19 June 2011 |archive-url=https://web.archive.org/web/20110619145941/http://apod.nasa.gov/apod/ap970711.html |url-status=live }}</ref>

Both rocks turned out to be [[andesite]]s; this finding surprised some scholars because andesites are formed by geological processes that require an interaction between materials of the [[Crust (geology)|crust]] and the [[Mantle (geology)|mantle]]. A lack of information on the surrounding highlands made it impossible to grasp all of the implications of the discovery.<ref name=andesit>{{cite web |url=http://marsprogram.jpl.nasa.gov/MPF/science/mineralogy.html |editor=Jet Propulsion Laboratory, NASA |title=Mars Pathfinder Science Results: Mineralogy and Geochemistry |access-date=15 December 2010 |archive-date=17 October 2011 |archive-url=https://web.archive.org/web/20111017233154/http://marsprogram.jpl.nasa.gov/MPF/science/mineralogy.html |url-status=live }}</ref>

The rover was then directed to the next target and on the 14th sol, it analyzed the rock named "Scooby-Doo" and imaged the "Casper" rock.<ref name="Operations" /> Both were deemed to be consolidated deposits.<ref name="Deposits" /> The rock called "Moe" showed evidence of [[wind erosion]]. Most of the rocks analyzed showed a high [[silicon]] content. In a region nicknamed "Rock Garden", the rover encountered crescent-moon-shaped dunes that are similar to dunes on earth.<ref name="geology" />

The landing site is rich in varied rocks, some of which are clearly volcanic in origin, such as "Yogi"; others are [[Conglomerate (rocks)|conglomerates]], the origins of which are the subject of several proposals. In one hypothesis, they formed in the presence of water in Mars' distant past.<ref name="Deposits" /> In support of this, high silicon contents would be detected. This could also be a consequence of [[sedimentation]] processes; rounded rocks of various sizes were discovered and the valley's shapes are compatible with a river channel environment.<ref name="Golombek97" /> Smaller, more rounded stones may also have been generated during a surface impact event.<ref name="Deposits" />

When the mission's final results were described in a series of articles in the journal ''Science'' (December 5, 1997), it was believed the rock Yogi had a coating of dust but was similar to the rock Barnacle Bill. Calculations suggested both rocks mostly contain [[orthopyroxene]] (magnesium-iron silicate), [[feldspars]] (aluminum silicates of potassium, sodium, and calcium), and quartz (silicon dioxide) with smaller amounts of [[magnetite]], [[ilmenite]], [[iron sulfide]], and [[calcium phosphate]].<ref name="nssdc.gsfc.nasa.gov">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/marspath/apxs.html |title=APXS Composition Results |work=NASA |access-date=June 10, 2015 |archive-url=https://web.archive.org/web/20160603120939/http://nssdc.gsfc.nasa.gov/planetary/marspath/apxs.html |archive-date=June 3, 2016 |url-status=live }}</ref><ref name="Bruckner, J. 2001">{{cite journal |last1=Bruckner |first1=J. |first2=G. |last2=Dreibus |first3=R. |last3=Rieder |first4=H. |last4=Wanke |year=2001 |title=Revised Data of the Mars Pathfinder Alpha Proton X-ray spectrometer: Geochemical Behavior of Major and Minor Elements |journal=Lunar and Planetary Science XXXII|page=1293 |bibcode=2001LPI....32.1293B }}</ref>
{{Wide image|PIA01153.jpg|1200px|Annotated panorama of rocks near the rover (December 5, 1997)}}

== ''Sojourner'' in popular culture ==
[[File:The Martian scene with Mars Pathfinder.jpg|thumb|Screenshot from ''[[The Martian (film)|The Martian]]'', depicting the protagonist Mark Watney with ''Pathfinder'' lander and ''Sojourner'' rover.]]

* In the 2000 film ''[[Red Planet (film)|Red Planet]]'', the crew of the first mission to Mars survives the crash-landing of their entry vehicle. Their communications equipment is destroyed so they cannot contact their recovery vehicle in orbit. To re-establish contact before being presumed dead and left behind on Mars, the crew goes to the site of the ''Pathfinder'' rover, from which they salvage parts to make a basic radio.<ref>Pfarrer, Chuck; Lemkin, Jonathan (2000). [http://www.dailyscript.com/scripts/red_planet.pdf "Red Planet"] {{Webarchive|url=https://web.archive.org/web/20150923212612/http://www.dailyscript.com/scripts/red_planet.pdf |date=2015-09-23 }} (PDF). The Daily Script. p. 45. Retrieved December 10, 2015.</ref>
* In the opening titles of the 2005 ''[[Star Trek: Enterprise]]'', ''Sojourner'' is shown lying dormant and covered in dust. Another scene shows a plaque marking the landing site of the rover on board the ''Carl Sagan Memorial Station''.<ref>{{cite web |url=http://www.imdb.com/title/tt0244365/crazycredits |title=Crazy credits for "Enterprise" |website=[[IMDb]] |editor=IMDb.com |access-date=24 November 2010 |archive-date=12 February 2011 |archive-url=https://web.archive.org/web/20110212032345/http://www.imdb.com/title/tt0244365/crazycredits |url-status=live }}</ref> In the episode "[[Terra Prime]]", ''Sojourner'' is briefly seen on the surface of Mars as a monument.
* In [[Andy Weir]]'s 2011 novel ''[[The Martian (Andy Weir)|The Martian]]'',<ref>{{cite book|last=Weir|first=Andy|title=[[The Martian (Andy Weir)|The Martian]]|year=2014|location=[[New York City|New York]]|publisher=[[Crown Publishers]]|isbn=978-0-8041-3902-1}}</ref> and [[The Martian (film)|the 2015 film based on it]],<ref>{{cite web |title='The Martian' – Anatomy of a Scene w/ Director Ridley Scott |url=https://www.youtube.com/watch?v=DqfnMzDhi38 |website=YouTube |publisher=The New York Times |access-date=13 August 2021 |archive-date=13 August 2021 |archive-url=https://web.archive.org/web/20210813072409/https://www.youtube.com/watch?v=DqfnMzDhi38 |url-status=live }}</ref> the protagonist Mark Watney is stranded on Mars. Mark recovers the ''Pathfinder'' lander and uses it to contact Earth. For the movie, the lander and rover were re-created with the help of JPL. Production designer Arthur Max, who worked on the film, said they "have a fully practical working ''Pathfinder'', which we use throughout the movie."<ref name='Fact check'>{{cite web |title=The real Mars lander in 'The Martian': Fact checking the film's NASA probe |url=http://www.collectspace.com/news/news-100215a-the-martian-mars-pathfinder.html |website=collectspace.com |publisher=[[collectSPACE]] |access-date=15 August 2021 }}</ref> In the movie, Mark Watney is later seen in his [[Colonization of Mars|Mars outpost]], the Ares III Hab, with the ''Sojourner'' roving around.

== Awards and honors ==
* 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 Society's Planetary Geology Division.<ref>{{Cite journal|title=Division Activity at Recent Meetings |journal=Planetary Geology Division Newsletter |volume=16 |issue=1 |pages=1 |date=1997 |url=https://www.unb.ca/passc/GSA/Newsletters.img/formatted%20newsletter%201998.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110608004417/http://www.unb.ca/passc/GSA/Newsletters.img/formatted%20newsletter%201998.pdf |archive-date=June 8, 2011 }}</ref>
* In November 1997, to commemorate the achievements of [[Mars Pathfinder]] program, a [[U.S. space exploration history on U.S. stamps#Mars Pathfinder|$3 Priority Mail stamp]] was issued. Fifteen million stamps were printed. The stamp is based on the first image received from the Mars Pathfinder after its landing on the Martian surface July 4, 1997, which shows the ''Sojourner'' rover resting on the Pathfinder with a panoramic view of the Ares Vallis region in the background. The stamp's reverse bears text about the Pathfinder mission.<ref>{{cite web |title=Mars Pathfinder Lands On U.S. Postage Stamp |url=https://mars.nasa.gov/MPF/mpf/stamp.html |website=mars.nasa.gov |publisher=NASA |access-date=15 August 2021 |archive-date=19 March 2021 |archive-url=https://web.archive.org/web/20210319235951/https://mars.nasa.gov/MPF/mpf/stamp.html |url-status=live }}</ref>
* ''Sojourner'' was included in the [[Robot Hall of Fame]] by [[Carnegie Mellon University]].<ref>{{cite web |url=http://www.robothalloffame.org/mars.html |title=The 2003 Inductees: Mars Pathfinder Sojourner Rover |editor=Carnegie Mellon University |access-date=15 December 2010|archive-url=https://web.archive.org/web/20071007211920/http://www.robothalloffame.org/mars.html | archive-date=7 October 2007 }}</ref>
* ''[[Perseverance (rover)|Perseverance]]'' rover, which landed in 2021, has a simplified representation of all previous NASA Martian rovers, starting with ''Sojourner'', on one of its external plates.<ref>{{cite web | url = https://www.space.com/perseverance-rover-mars-robots-family-portrait | title = NASA's Perseverance rover on Mars is carrying an adorable 'family portrait' of Martian rovers | first = Hanneke | last = Weitering | date = February 25, 2021 | access-date = July 14, 2021 | work = [[Space.com]] | archive-date = July 14, 2021 | archive-url = https://web.archive.org/web/20210714214008/https://www.space.com/perseverance-rover-mars-robots-family-portrait | url-status = live }}</ref>

== Key personnel ==
The development of the rover and its instruments as well as its guidance during operations on Mars were done by a group of engineers from NASA, collectively referred to as "The Rover Team". The key personnel were:<ref name="washington" />
* Microrover Flight Experiment Manager: [[Jacob Matijevic]], JPL
* Chief Engineer, Microrover Flight Experiment: William Layman, JPL
* Assembly and Lead Test Engineer, Microrover Flight Experiment, Allen Sirota, JPL
* Microrover Mission Operations Engineer: [[Andrew Mishkin]], JPL
* IMP Principal investigator: Peter H. Smith, [[University of Arizona]]
* ASI/MET Facility Instrument Science Team Leader: John T. Schofield, JPL
* ASI/MET Chief Engineer: Clayton LaBaw, JPL
* APXS Principal investigator: Rudolf Rieder, [[Max-Planck Institute]], Department of Chemistry, Mainz, Germany
* Wheel Abrasion Experiment, Principal investigators: D. Ferguson and J. Kolecki, [[NASA Lewis Research Center]]
* Material Adherence Experiment, Principal investigators: G. Landis and P. Jenkins, NASA Lewis Research Center
* Manager of the Mars Exploration Program at JPL: [[Donna Shirley]]

== Gallery ==
<gallery mode="packed" heights="150px">
File:Sojourner.gif|''Sojourner'' in the production phase.
File:Mars Pathfinder Lander preparations.jpg|''Pathfinder'' and ''Sojourner'' at JPL in October 1996, being 'folded' into its launch position.
File:Mars Pathfinder Preparations - GPN-2000-000787.jpg|Mars Pathfinder loading into a rocket.
</gallery>
<gallery mode="packed" heights="150px">
File:PIA01551.jpg|The sol 2 "insurance panorama" of ''Sojourner'', taken on 530, 600, and 750&nbsp;nm filters.{{efn|Image was taken by IMP before the mast was deployed. It was called "insurance panorama", because if something went wrong during deployment, the team would still have a panorama of the landing site. Once the mast was deployed the height of the IMP was constant.<ref name="howimpworks" />}}
File:Pathfinder01.jpg|''Sojourner'' performs spectrometer measurements on the "Yogi" rock.
File:PIA01238.jpg|Route of the rover projected on an image taken by the lander.
File:PIA02652.jpg|Mosaic of the lander and the rover from above, color has been enhanced to improve contrast in features, and is derived from IMP spectral filters 5, 9 and 0.
File:Rover movie sol10 S0050F with Yogi.gif|Rover near Yogi, sol 10.
</gallery>
{{Wide image|PIA01466.jpg|1200px|''Mars Pathfinder'' panorama of landing site taken by lander's camera (IMP)}}
{{Wide image|Mars Pathfinder Presidential Panorama.jpg|1200px|Various images of the ''Sojourner'' shot by the lander have been composited into the 360 degree Presidential Panorama. Since the camera's position was consistent, it is thus possible to see these images of the rover in the context of the entire landscape. This provides a visual scale for understanding the sizes and distances of rocks surrounding the lander as well as a record of the travels of the rover. Several of the rover images were captured in full color. The rest were colorized using color sampled from those frames.<ref>{{cite web |title=Presidential Panorama |url=https://mars.nasa.gov/MPF/ames/ames-rovers.html |website=mars.nasa.gov |publisher=NASA |access-date=30 August 2021 |archive-date=23 June 2021 |archive-url=https://web.archive.org/web/20210623060402/https://mars.nasa.gov/MPF/ames/ames-rovers.html |url-status=live }}{{PD-notice}}</ref>}}

=== Comparison to later Mars rovers ===
[[File:PIA15279 3rovers-stand D2011 1215 D521.jpg|thumb|center|800px|Two spacecraft engineers stand with a group of vehicles providing a comparison of three generations of Mars rovers developed at NASA's Jet Propulsion Laboratory. The setting is JPL's Mars Yard testing area. Front and center is the flight spare for the first Mars rover, ''Sojourner'', which landed on Mars in 1997 as part of the [[Mars Pathfinder]] Project. On the left is a [[Mars Exploration Rover]] Project (MER) test rover that is a working sibling to ''[[Spirit (rover)|Spirit]]'' and ''[[Opportunity (rover)|Opportunity]]'', which landed on Mars in 2004. On the right is a [[Mars Science Laboratory]] test rover the size of that project's Mars rover, ''[[Curiosity (rover)|Curiosity]]'', which landed on Mars in 2012. ''Sojourner'' and its flight spare, ''Marie Curie'', are 65&nbsp;cm long. The MER's rovers are 1.6 m long. The ''Curiosity'' rover is 3&nbsp;m long.]]

<gallery mode="packed" caption="Comparison of wheels of ''Sojourner'', ''Spirit'' and ''Opportunity'', and ''Curiosity'' rovers.">
File:H rover-comp wheels 02.jpg
File:Mars rovers wheels nested.jpg
File:Mars wheels compared to 14inch disk.jpg
</gallery>
{{clear}}

== ''Sojourner''{{'}}s location in context ==
{{Clear}}
{{Mars map indicating landers}}
{{Clear}}

== See also ==
* [[Exploration of Mars]]
* [[Mars 3|''Mars 3'' (lander)]]
* [[Viking 1|''Viking 1'' (lander)]]
* [[Viking 2|''Viking 2'' (lander)]]
* [[Spirit (rover)|''Spirit'' (rover)]]
* [[Opportunity (rover)|''Opportunity'' (rover)]]
* [[Curiosity (rover)|''Curiosity'' (rover)]]
* [[Perseverance (rover)|''Perseverance'' (rover)]]
* [[Zhurong (rover)|''Zhurong'' (rover)]]
* [[Rosalind Franklin (rover)|''Rosalind Franklin'' (rover)]] (planned mission)
* [[Comparison of embedded computer systems on board the Mars rovers]]

== Footnotes ==
{{notelist}}

== References ==
{{reflist|2}}
Some sections of this article were originally translated from the Italian Wikipedia article. For original, see [[:it:Sojourner]].

== Further reading ==
* {{cite book| author=[[Andrew Mishkin]] |title=Sojourner: An Insider's View of the Mars Pathfinder Mission |url=https://archive.org/details/sojournerinsider00mish |year=2004 |publisher=Berkeley Books |editor=Berkeley Books |isbn=978-0-425-19839-1 }}
* {{cite journal| author=The Rover Team |title=The Pathfinder Microrover
|year=1997 |journal=J. Geophys. Res. |volume=102 | number=E2 |pages=3989–4001 |doi=10.1029/96JE01922 |bibcode=1997JGR...102.3989M
}}

== External links ==
{{Commons category|Mars Pathfinder (rover)}}
* {{cite web |url=http://mars.jpl.nasa.gov/MPF/mpf/rover.html |title=Rover Sojourner |website=Mars Pathfinder Mission |editor=JPL, NASA |access-date=24 September 2010}}
* {{cite web |url=http://marsprogram.jpl.nasa.gov/MPF/roverview/table.html |title=Mars As Seen Through the Eyes of the Sojourner Rover |website=Mars Pathfinder Mission |editor=JPL, NASA |access-date=24 September 2010}}
*{{official|http://www.nasa.gov/mission_pages/mars-pathfinder/}}
*[https://mars.nasa.gov/MPF/rovercom/pix.html Mars Microrover Photo Gallery]
*[http://mars.jpl.nasa.gov/MPF/mpf/image-arc.html Directory of ''Pathfinder'' images]
*[https://mars.nasa.gov/MPF/ops/rover.html Logbook of Rover Operations]
*[https://www.sciencefriday.com/articles/archive-mars-pathfinder-sojourner/ How The Age Of Mars Rovers Began] by Lauren J. Young on [[Science Friday]]
* [https://www.youtube.com/watch?v=v63ZwrHAKxg ''Mars Pathfinder'' Media Reel] by JPL on YouTube

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