Sojourner (rover)

Sojourner is a robotic Mars rover that landed on July 4, 1997[1] in the Ares Vallis region. The rover was the first wheeled vehicle to rove another planet, and was part of the Mars Pathfinder mission.[2] It had front and rear cameras and hardware to conduct several scientific experiments. Designed for a mission lasting 7 sols, with possible extension to 30 sols,[3] it was ultimately active for 83 sols (85 Earth days). The rover communicated with Earth through the Pathfinder base station, which had its last communication session with Earth at 3:23 a.m. PDT on September 27, 1997.[1][4] This marked the end of the Sojourner mission as well. Sojourner traveled a distance of just over 100 meters (330 ft) by the time communication was lost.[5] It was instructed to stay stationary until October 5, 1997 (sol 91) and then drive around the lander.[6]

Sojourner on Mars PIA01122.jpg
Soujourner rover pictured by Pathfinder lander
Mission typeMars rover
WebsiteOfficial website
Mission durationPlanned: 7 sols (7 days)
Mission end: 83 sols (85 days)
From arrival on Mars
Spacecraft properties
Dry mass11.5 kilograms (25 lb) (Rover only)
Start of mission
Launch dateDecember 6, 1996, 06:58:07 UTC
RocketDelta II 7925 D240
Launch siteCape Canaveral LC-17B
ContractorMcDonnell Douglas
Deployed fromMars Pathfinder
Deployment dateJuly 5, 1997 (1997-07-05)
End of mission
Last contactSeptember 27, 1997 (1997-09-28)
Mars rovers (NASA)
Sojourner rover on Mars, as stowed on one of the station petals
A color image taken by the Sojourner rover of its wheel leaving tracks on Mars
Sojourner view of Mars Pathfinder base station (Sagan Memorial Station) after driving off the ramps onto Mars


The name of the rover was selected in an essay contest won by Valerie Ambroise, a 12-year-old from U.S. state of Connecticut. It is named for abolitionist and women's rights activist Sojourner Truth.[7] The second-place prize went to Deepti Rohatgi, 18, of Rockville, who proposed Marie Curie, a Nobel Prize-winning Polish chemist. Third place went to Adam Sheedy, 16, of Round Rock, TX, who chose Judith Resnik, a United States astronaut and shuttle crew-member.[8] The rover was also known as Microrover Flight Experiment abbreviated MFEX.[9]

Sojourner has solar panels and a non-rechargeable battery, which allowed limited nocturnal operations. Once the batteries were depleted, it could only operate during the day.[3] The batteries are lithium-thionyl chloride (LiSOCl2) and could provide 150 watt-hours.[10] The batteries also allowed the health of the rover to be checked while enclosed in the cruise stage while en route to Mars.[11]

0.22 square meters of solar cells could produce a maximum of about 15 watts on Mars, depending on conditions.[10] The cells were GaAs/Ge (Gallium Arsenide/Germanium) and capable of about 18 percent efficiency. They could survive down to about −140° Celsius (−220 °F).[11]

Its central processing unit (CPU) is an 80C85 with a 2 MHz clock, addressing 64 Kbytes of memory. It has four memory stores; the previously mentioned 64 Kbytes of RAM (made by IBM) for the main processor, 16 Kbytes of radiation-hardened PROM (made by Harris), 176 Kbytes of non-volatile storage (made by Seeq Technology), and 512 Kbytes of temporary data storage (made by Micron). The electronics were housed inside the Warm Electronics Box inside the rover.[3]

Sojourner communicated with its base station using a 9,600 baud radio modem, although error-checking protocols limited communications to a functional data rate of 2,400 baud with a theoretical range of about half a kilometer. Under normal operation, it would periodically send a "heartbeat" message to the lander. If no response was given, the rover could autonomously travel back to the location at which the last heartbeat was received. If desired, this 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 10 meters from Pathfinder during its mission.[3]

The UHF radio modems worked similar to walkie-talkies, but sent data, not voice. It could send or receive, but not both at same time, which is known as half-duplex. The data was communicated in bursts of 2 kilobytes.[12]

The Alpha Proton X-ray Spectrometer (APXS) is nearly identical to the one on Mars 96, and was a collaboration between the Max Planck Institute for Solar System Research in Lindau, Germany (formally known as the Max Planck Institute For Aeronomy) and the University of Chicago in the United States. APXS could determine elemental composition of Mars rocks and dust, except for hydrogen. It works by exposing a sample to alpha particles, then measuring the energies of emitted protons, X-rays, and backscattered alpha particles.[13]

The rover had three cameras: two monochrome cameras in front, and a color camera in the rear. Each front camera had an array 484 pixels high by 768 wide. The optics consisted of a window, lens, and field flattener. The window was made of sapphire, while the lens objective and flattener were made of zinc selenide.[14] The rover was imaged on Mars by the base station's IMP camera system, which also helped determine where the rover should go.[9]

Sojourner operation was supported by "Rover Control Software", which ran on a Silicon Graphics Onyx2 computer back on Earth, and allowed command sequences to be generated using a graphical interface.[15] The rover driver would wear 3D goggles supplied with imagery from the base station and move a virtual model with the spaceball controller, a specialized joystick. The control software allowed the rover and surrounding terrain to be viewed from any angle or position, supporting the study of terrain features, placing waypoints, or doing virtual flyovers.[15]

The rover had a mass of 11.5 kg (weighing about 25 pounds on Earth), which equates to a weight of 4.5 kgf (10 pounds) on Mars.[5]

In popular cultureEdit

  • In the 2000 film Red Planet, the crew of the first manned mission to Mars survives the crash-landing of their entry vehicle, but their communications equipment is destroyed so they cannot contact their recovery vehicle in orbit. To reestablish contact before being presumed dead and left behind by the pilot of their recovery vehicle, the crew goes to the site of the Pathfinder rover, from which they salvage parts to make a basic radio.[16]
  • In the 2005 season 4 Star Trek: Enterprise episode "Terra Prime", Sojourner is briefly seen on the surface of Mars as a monument.
    • Sojourner also features in Enterprises's opening sequence.
  • In the 2011 novel The Martian by Andy Weir, and the 2015 film based on it, the protagonist Mark Watney, stranded on Mars, recovers the Pathfinder lander, and is able to use it to contact Earth.[17] In the movie, he is later seen in his Mars outpost, the Ares III Hab, with the Sojourner roving around.


The Sol 2 "insurance panorama" of Sojourner, taken on 530,600, and 750 nm filters

Sojourner's location in contextEdit

Acheron FossaeAcidalia PlanitiaAlba MonsAmazonis PlanitiaAonia PlanitiaArabia TerraArcadia PlanitiaArgentea PlanumArgyre PlanitiaChryse PlanitiaClaritas FossaeCydonia MensaeDaedalia PlanumElysium MonsElysium PlanitiaGale craterHadriaca PateraHellas MontesHellas PlanitiaHesperia PlanumHolden craterIcaria PlanumIsidis PlanitiaJezero craterLomonosov craterLucus PlanumLycus SulciLyot craterLunae PlanumMalea PlanumMaraldi craterMareotis FossaeMareotis TempeMargaritifer TerraMie craterMilankovič craterNepenthes MensaeNereidum MontesNilosyrtis MensaeNoachis TerraOlympica FossaeOlympus MonsPlanum AustralePromethei TerraProtonilus MensaeSirenumSisyphi PlanumSolis PlanumSyria PlanumTantalus FossaeTempe TerraTerra CimmeriaTerra SabaeaTerra SirenumTharsis MontesTractus CatenaTyrrhen TerraUlysses PateraUranius PateraUtopia PlanitiaValles MarinerisVastitas BorealisXanthe Terra 
 Interactive image map of the global topography of Mars, overlain with locations of Mars landers and rovers. Hover over the image to see the names of over 60 prominent geographic features, and click to link to them. Coloring of the base map indicates relative elevations, based on data from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor. Whites and browns indicate the highest elevations (+12 to +8 km); followed by pinks and reds (+8 to +3 km); yellow is 0 km; greens and blues are lower elevations (down to −8 km). Axes are latitude and longitude; Polar regions are noted.
(   Rover  Lander  Future )

Comparison to later Mars-craftEdit

A comparison of sizes for the Sojourner rover, the Mars Exploration Rovers (Spirit and Opportunity), the Phoenix lander and the Mars Science Laboratory (Curiosity).

See alsoEdit


  1. ^ a b Nelson, Jon. "Mars Pathfinder / Sojourner Rover". NASA. Retrieved February 2, 2014.
  2. ^ Siddiqi, Asif A. (2018). Beyond Earth: A Chronicle of Deep Space Exploration, 1958–2016 (PDF). The NASA history series (second ed.). Washington, DC: NASA History Program Office. p. 2. ISBN 9781626830424. LCCN 2017059404. SP2018-4041.
  3. ^ a b c d "Mars Pathfinder FAQs - Sojourner".
  4. ^ "Mars Pathfinder - Mars - Sol 86 Images".
  5. ^ a b "Sojourner". Archived from the original on 2015-03-20.
  6. ^ "Mars Pathfinder - Mars - Sol 89 Images".
  7. ^ "Girl Who Named Mars Rover Stays Down to Earth". The New York Times. 1997-07-14. ISSN 0362-4331. Retrieved 2019-01-24.
  8. ^ "Pathfinder Rover Gets Its Name".
  9. ^ a b "Mars Pathfinder Microrover Ready to Roll!".
  10. ^ a b "Description of the Rover Sojourner".
  11. ^ a b "Mars Pathfinder Microrover".
  12. ^ "How the Mars Microrover Radios and Antennas Work".
  13. ^ "Mars Pathfinder Instrument Descriptions".
  14. ^ "Rover Camera Instrument Description".
  15. ^ a b "MFEX Electronics".
  16. ^ Pfarrer, Chuck; Lemkin, Jonathan (2000). "Red Planet" (PDF). The Daily Script. pg. 45. Retrieved December 10, 2015.
  17. ^ Weir, Andy (2014). The Martian. New York: Crown Publishers. ISBN 978-0-8041-3902-1.

External linksEdit