 | |
| Mission type | Lander · Rover |
|---|---|
| Operator | NASA · Jet Propulsion Laboratory |
| COSPAR ID | 1996-068A |
| SATCATno. | 24667 |
| Website | mars |
| Mission duration | 85 days Launch to last contact: 9 months, 23 days |
| Spacecraft properties | |
| Launch mass | 890 kg (includes propellant)[2] |
| Power | Pathfinder: 35 W Sojourner: 13 W |
| Start of mission | |
| Launch date | December 4, 1996 (1996-12-04) 06:58:07UTC |
| Rocket | Delta II 7925 (#D240) |
| Launch site | Cape CanaveralSLC-17 |
| Contractor | None[3] |
| End of mission | |
| Last contact | September 27, 1997 (1997-09-27) 10:23UTC |
| Mars lander | |
| Landing date | July 4, 1997; 28 years ago (1997-07-04) 16:56:55UTC MSD 43905 04:41AMT |
| Landing site | Ares Vallis,Chryse Planitia,Mars 19°7′48″N33°13′12″W / 19.13000°N 33.22000°W /19.13000; -33.22000 (Sojourner rover (Mars Pathfinder)) |
| Transponders | |
| Band | X-Band with high-gain antenna |
| Bandwidth | 6 kb/s to 70 mDeep Space Network, 250 b/s to surface command[2] |
 Official insignia of theMars Pathfinder mission. | |
Mars Pathfinder[1] was an Americanrobotic spacecraft that landed a base station with aroving probe onMars in 1997. It consisted of alander, renamed theCarl Sagan Memorial Station, and a lightweight, 10.6 kg (23 lb) wheeledroboticMars rover namedSojourner,[4] the first rover to operate outside the Earth–Moon system. The mission terminated in 1998.
Launched on December 4, 1996, byNASA aboard aDelta II booster a month after theMars Global Surveyor, it landed on July 4, 1997, onMars'sAres Vallis, in a region calledChryse Planitia in theOxia Palus quadrangle. Thelander then opened, exposing the rover which conducted many experiments on the Martian surface. The mission carried a series of scientific instruments to analyze the Martianatmosphere,climate, and geology and the composition of itsrocks and soil. It was the second project from NASA'sDiscovery Program, which promotes the use of low-cost spacecraft and frequent launches under the motto "cheaper, faster and better" promoted by then-administratorDaniel Goldin. The mission was directed by theJet Propulsion Laboratory (JPL), a division of theCalifornia Institute of Technology, responsible for NASA'sMars Exploration Program. The project manager was JPL'sTony Spear.
This mission was the first of a series of missions to Mars that included rovers, and was the first successful lander since the twoVikings landed on Mars in 1976. Although theSoviet Union successfully sent rovers to the Moon as part of theLunokhod program in the 1970s, its attempts to use rovers in itsMars program failed.
In addition to scientific objectives, theMars Pathfinder mission was also a "proof-of-concept" for various technologies, such asairbag-mediated touchdown and automated obstacle avoidance, both later exploited by theMars Exploration Rover mission. TheMars Pathfinder was also remarkable for its extremely low cost relative to other robotic space missions to Mars. Originally, the mission was conceived as the first of theMars Environmental Survey (MESUR) program.[5]
TheMars Pathfinder conducted different investigations on the Martian soil using three scientific instruments. The lander contained astereoscopic camera with spatial filters on an expandable pole called Imager for Mars Pathfinder (IMP),[8][9] and the Atmospheric Structure Instrument/Meteorology Package (ASI/MET)[10] which acted as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure included threewindsocks mounted at three heights on a pole, the topmost at about one meter (3.3 ft) and generally registered winds from the West.[11]
TheSojourner rover had an Alpha Proton X-ray Spectrometer (APXS),[12] which was used to analyze the components of the rocks and soil. The rover also had two black-and-white cameras and a color one. These instruments could investigate the geology of the Martian surface from just a few millimeters to many hundreds of meters, thegeochemistry and evolutionary history of the rocks and surface, themagnetic andmechanical properties of the land, as well as the magnetic properties of the dust, atmosphere and therotational andorbital dynamics of the planet.
The rover was equipped with threeCCD cameras, all manufactured byEastman Kodak Company and controlled by the rover's CPU. The two front-facing monochrome cameras served navigation purposes and were coupled with five laser stripe projectors forstereoscopic hazard detection. These front cameras had a resolution of 484 vertical by 768 horizontal pixels, and anoptical resolution capable of discerning details as small as 0.6 cm (0.24 in) across a range of 0.65 m (26 in). Images from these cameras could be compressed using theblock truncation coding (BTC) algorithm.
The third camera, situated at the rear near the APXS, was used for color imaging. It shared the resolution of the front cameras but was rotated 90 degrees to capture images of both the APXS target area and the rover's tracks. This rear camera featured a 4x4 pixel block with specific color sensitivities: 12 pixels for green, two for red, and two forinfrared. All cameras employedlenses made ofzinc selenide, which blocks light wavelengths below 500 nm; as a result, the blue/infrared pixels effectively detected only infrared light. Each camera had auto-exposure and bad-pixel handling functions. Image parameters, such as exposure time and compression settings, were included in the transmitted image headers. If BTC compression was to be used on the rear camera, the color information would need to be discarded.[13]
The IMP had a set of filters designed to record surface and atmospheric phenomena. There were two cameras, or eyes, allowing forstereoscopic imagery, with the set of filters being slightly different between them.[16][17][18]
| Eye and Filter | Center Wavelength (nm) | Bandwidth (nm) | Category |
|---|---|---|---|
| L0 | 443 | 26 | Stereo, Geology |
| L5 | 671 | 20 | Stereo, Geology |
| L6 | 802 | 21 | Geology |
| L7 | 858 | 34 | Geology |
| L8 | 898 | 41 | Geology |
| L9 | 931 | 27 | Stereo, Ranging, Geology |
| L10 | 1003 | 29 | Geology |
| L11 | 968 | 31 | Stereo, Ranging, Geology |
| R0 | 443 | 26 | Stereo, Geology |
| R5 | 671 | 20 | Stereo, Geology |
| R6 | 752 | 19 | Geology |
| R8 | 600 | 21 | Geology |
| R9 | 531 | 30 | Stereo, Ranging, Geology |
| R10 | 480 | 27 | Geology |
| R11 | 967 | 30 | Stereo, Ranging, Geology |
| L1 | 450 | 5 | Solar |
| L2 | 883 | 6 | Solar |
| L3 | 925 | 5 | Solar |
| L4 | 935 | 5 | Solar |
| R1 | 670 | 5 | Solar |
| R2 | 946 | 44 | Solar |
| R3 | 936 | 5 | Solar |
| R4 | 989 | 5 | Solar |
The ASI/MET recorded temperature, pressure and wind data, during entry and descent, and once on the surface.[16] It also housed electronics for sensor operation and data recording.[16]
The landing site was an ancient flood plain in Mars's northern hemisphere called "Ares Vallis" ("the valley of Ares", the ancient Greek equivalent of the ancient Roman deity Mars) and is among the rockiest parts of Mars. Scientists chose it because they found it to be a relatively safe surface to land on and one that contained a wide variety of rocks deposited during a catastrophic flood. After the landing, at19°08′N33°13′W / 19.13°N 33.22°W /19.13; -33.22,[20] succeeded, the lander received the nameTheCarl Sagan Memorial Station in honor of theastronomer.[21] (See alsoList of extraterrestrial memorials)
Mars Pathfinder entered the Martian atmosphere and landed using an innovative system involving an entry capsule, a supersonicparachute, followed by solid rockets and large airbags to cushion the impact.
Mars Pathfinder directly entered Mars atmosphere in a retrograde direction from a hyperbolic trajectory at 6.1 km/s (14,000 mph) using an atmospheric entry aeroshell (capsule) that was derived from the original Viking Mars lander design. The aeroshell consisted of a back shell and a specially designed ablative heatshield to slow to 370 m/s (830 mph) where a supersonic disk-gap-band parachute was inflated to slow its descent through the thin Martian atmosphere to 68 m/s (150 mph). The lander's on-board computer used redundant on-board accelerometers to determine the timing of the parachute inflation. Twenty seconds later the heatshield was pyrotechnically released. Another twenty seconds later the lander was separated and lowered from the backshell on a 20 m (66 ft) bridle. When the lander reached 1.6 km (5,200 ft) above the surface, a radar was used by the on-board computer to determine altitude and descent velocity. This information was used by the computer to determine the precise timing of the landing events that followed.[22]
Once the lander was 355 m (1,165 ft) above the ground, airbags were inflated in less than a second using three gas generators.[23] The airbags were made of four inter-connected multi-layervectran bags that surrounded the tetrahedron lander. They were designed and tested to accommodate grazing angle impacts as high as 28 m/s (63 mph). However, as the airbags were designed for no more than about 15 m/s (34 mph) vertical impacts, three solid retrorockets were mounted above the lander in the backshell.[24] These were fired at 98 m (322 ft) above the ground. The lander's on-board computer estimated the best time to fire the rockets and cut the bridle so that the lander velocity would be reduced to about zero between 15 and 25 m (49 and 82 ft) above the ground. After 2.3 seconds, while the rockets were still firing, the lander cut the bridle loose about 21.5 m (71 ft) above the ground and fell to the ground. The rockets flew up and away with the backshell and parachute (they have since been sighted by orbital images). The lander impacted at 14 m/s (31 mph) and limited the impact to only 18 G of deceleration. The first bounce was 15.7 m (52 ft) high and the lander continued bouncing for at least 15 additional bounces (accelerometer data recording did not continue through all of the bounces).[25]
The entire entry, descent and landing process was completed in four minutes.
Once the lander stopped rolling, the airbags deflated and retracted toward the lander using four winches mounted on the lander "petals". Designed to right itself from any initial orientation, the lander happened to roll right side up onto its base petal. Eighty-seven minutes after landing, the petals were deployed withSojourner rover and the solar panels attached on the inside.[26]
The lander arrived at night at 2:56:55 Mars local solar time (16:56:55 UTC) on July 4, 1997. The lander had to wait until sunrise to send its first digital signals and images to Earth. The landing site was located at 19.30° north latitude and 33.52° west longitude in Ares Vallis, only 19 km (12 mi) southwest of the center of the 200 km (120 mi) wide landing site ellipse. DuringSol 1, the first Martian solar day the lander spent on the planet, the lander took pictures and made some meteorological measurements. Once the data was received, the engineers realized that one of the airbags had not fully deflated and could be a problem for the forthcoming traverse ofSojourner's descent ramp. To solve the problem, they sent commands to the lander to raise one of its petals and perform additional retraction to flatten the airbag. The procedure was a success and on Sol 2,Sojourner was released, stood up and backed down one of two ramps.[26]
TheSojourner rover departed from the lander on Sol 2, after its landing on July 4, 1997. As the next sols progressed it approached some rocks, which the scientists named "Barnacle Bill", "Yogi", and "Scooby-Doo", after famouscartoon characters. The rover made measurements of the elements found in those rocks and in the martian soil, while the lander took pictures of theSojourner and the surrounding terrain, in addition to making climate observations.
TheSojourner is a six-wheeled, 65 cm (26 in) long vehicle, 48 cm (19 in) wide, 30 cm (12 in) tall and weighing 10.5 kg (23 lb).[27] Its maximum speed reached 1 cm/s (0.39 in/s).Sojourner travelled approximately 100 m (330 ft) in total, never more than 12 m (39 ft) from thePathfinder station. During its 83sols of operation, it sent 550 photographs to Earth and analyzed thechemical properties of 16 locations near the lander. (See alsoSpace exploration rovers)
The first analysis on a rock started on Sol 3 with Barnacle Bill. TheAlpha Particle X-ray Spectrometer (APXS) was used to determine its composition, the spectrometer taking ten hours to make a full scan of the sample. It found all the elements excepthydrogen, which constitutes just 0.1 percent of the rock's or soil's mass.
The APXS works by irradiating rocks and soil samples withalpha particles (heliumnuclei, which consist of twoprotons and twoneutrons). The results indicated that "Barnacle Bill" is much like Earth'sandesites, confirming pastvolcanic activity. The discovery of andesites shows that some Martian rocks have been remelted and reprocessed. On Earth, andesite forms when magma sits in pockets of rock while some of the iron and magnesium settle out. Consequently, the final rock contains less iron and magnesiums and more silica. Volcanic rocks are usually classified by comparing the relative amount of alkalis (Na2O and K2O) with the amount of silica (SiO2). Andesite is different from the rocks found in meteorites that have come from Mars.[28][29][30]
Analysis of the Yogi rock again using the APXS showed that it was abasaltic rock, more primitive than Barnacle Bill. Yogi's shape and texture show that it was probably deposited there by aflood.
Another rock, named Moe, was found to have certain marks on its surface, demonstrating erosion caused by the wind. Most rocks analyzed showed a high content ofsilicon. In another region known as Rock Garden,Sojourner encountered crescent moon-shaped dunes, which are similar tocrescentic dunes on Earth.
By the time that final results of the mission were described in a series of articles in the journalScience (December 5, 1997), it was believed that the rock Yogi contained a coating of dust, but was similar to the rock Barnacle Bill. Calculations suggest that the two rocks contain mostly the minerals orthopyroxene (magnesium-iron silicate), feldspars (aluminum silicates of potassium, sodium, and calcium), and quartz (silicon dioxide), with smaller amounts of magnetite, ilmenite, iron sulfide, and calcium phosphate.[28][29][30]
Theembedded computer on board theSojourner rover was based around the 2 MHz[31]Intel 80C85CPU with 512 KB ofRAM and 176 KB offlash memorysolid-statestorage, running acyclic executive.[32]
The computer of thePathfinder lander was aRadiation Hardened IBM Risc 6000 Single Chip (Rad6000 SC)CPU with 128 MB of RAM and 6 MB ofEEPROM[33][34] and itsoperating system wasVxWorks.[35]
The mission was jeopardised by aconcurrent software bug in the lander,[36] which had been found in preflight testing but was deemed a glitch and therefore given a low priority as 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 thanks to the logging and debugging functionality enabled in the flight software, was due tocomputer resets caused bypriority inversion. No scientific or engineering data was lost after a computer reset, but all the following operations were interrupted until the next day.[37][38] Four resets occurred (on July 5, 10, 11 and 14) during the mission,[39] before patching the software on July 21 to enablepriority inheritance.[40]
The lander sent more than 2.3 billion bits (287.5 megabytes) of information including 16,500 pictures and made 8.5 million measurements of theatmospheric pressure, temperature and wind speed.[41]
By taking multiple images of the sky at different distances from the Sun, scientists were able to determine that the size of the particles in the pink haze was about onemicrometre in radius. The color of some soils was similar to that of an iron oxyhydroxide phase which would support the theory of a warmer and wetter climate in the past.[42]Pathfinder carried a series of magnets to examine the magnetic component of the dust. Eventually, all but one of the magnets developed a coating of dust. Since the weakest magnet did not attract any soil, it was concluded that the airborne dust did not contain puremagnetite or just one type ofmaghemite. The dust probably was an aggregate possibly cemented withferric oxide (Fe2O3).[43] Using much more sophisticated instruments,MarsSpirit rover found that magnetite could explain the magnetic nature of the dust and soil on Mars. Magnetite was found in the soil and the most magnetic part of the soil was dark. Magnetite is very dark.[44]
UsingDoppler tracking andtwo-way ranging, scientists added earlier measurements from theViking landers to determine that the non-hydrostatic component of the polarmoment of inertia is due to theTharsis bulge and that the interior is not melted. The central metallic core is between 1,300 and 2,000 km (810 and 1,240 mi) in radius.[28]
Although the mission was planned to last from a week to a month, the rover operated successfully for almost three months. Communication failed after October 7,[45] with a final data transmission received from Pathfinder at 10:23 UTC on September 27, 1997. Mission managers tried to restore full communications during the following five months, but the mission was terminated on March 10, 1998. During the extended operation a high-resolution stereo panorama of the surrounding terrain was being made, and the Sojourner rover was to visit a distant ridge, but the panorama was only about one-third completed and the ridge visit had not begun when communication failed.[45]
The on-board battery—designed to operate for one month—may have failed after repeated charging and discharging. The battery was used to heat the probe's electronics to slightly above the expected nighttime temperatures on Mars. With the failure of the battery, colder-than-normal temperatures may have caused vital parts to break, leading to loss of communications.[45][46] The mission had exceeded its goals in the first month.
Mars Reconnaissance Orbiter spotted thePathfinder lander in January 2007 (see photo).[47][48]
The nameSojourner was chosen for theMars Pathfinder rover when 12-year old Valerie Ambroise, of Bridgeport, Connecticut, won a year-long, worldwide competition in which students up to 18 years old were invited to select a heroine and submit an essay about her historical accomplishments. The students were asked to address in their essays how a planetary rover named for their heroine would translate these accomplishments to the Martian environment.
Initiated in March 1994 byThe Planetary Society of Pasadena, California, in cooperation with NASA's Jet Propulsion Laboratory (JPL), the contest got under way with an announcement in the January 1995 issue of the National Science Teachers Association's magazineScience and Children, circulated to 20,000 teachers and schools across the nation.[49]
Ambroise's winning essay, which suggested naming the rover for the 19th century women's rights activistSojourner Truth, was selected from among 3,500 essays. First runner-up was Deepti Rohatgi, 18, of Rockville, Maryland, who suggested scientistMarie Curie. Second runner-up was Adam Sheedy, 15, of Round Rock, Texas, who submitted the name of the late astronautJudith Resnik, who perished in the 1986Space ShuttleChallenger explosion. Other popular suggestions included explorer and guideSacajewea and aviatorAmelia Earhart.[50]
| Mars Pathfinder (Carl Sagan Memorial Station) | | |
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| Mars Pathfinder instruments | ||
| Key personnel | ||
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| Rovers |  | |
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| Helicopter | ||
| Landers | ||
| Memorial sites | ||
| Sample depots | ||
† indicates a mission failure (no significant data returned from the surface). | ||
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