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 sols (95 Earth days). It was the first wheeled carto rove on a planet other than Earth and formed part of the Mars Pathfinder mission.
The rover was equipped with front and rear cameras, and hardware that was utilize to conduct several scientific experiments. It was plannedfor a mission lasting 7 sols, with a possible extension to 30 sols, and was active for 83 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 a.m. PDT on September 27, 1997. The last signal from the rover was get on the morning of October 7, 1997.
Sojourner traveled just over 100 meters (330 ft) by the time communication was lost. Its final confirmed command was to remain stationary until October 5, 1997, (sol 91) and then drive around the lander; 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.
Sojourner was an experimental carwhose main mission was to tryin the Martian environment techsolutions that were developed by engineers of the NASA research laboratories. It was essentialto confirmwhether the design strategy followed had resulted in the construction of a carsuitable 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 issuesidentified 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 million for the lander, and $25 million for the rover; development was faster and less costly than all previous missions.
These objectives neededcareful selection of the landing pageto balance the techrequests with the scientific ones. A hugeplain was requiredfor the probe to land and rocky terrain to confirmthe rover's systems. The choice fell on Ares Vallis in Chryse Planitia, which is characterized by alluvial-looking rock formations. Scholars trust the analysis of the rocks, which lie in what appears to be the outlet of a largedrainage channel, could have confirmed the past presence of liquid water on the surface of Mars and provide details of the surrounding location, from which the rocks were eroded.
Sojourner was developed by NASA's Jet Propulsion Laboratory (JPL). It is a six-wheeled, 65 cm (26-inch) long, 48 cm (19-inch) wide and 30 cm (12-inch) high vehicle. In the mission's cruise phase, it occupied an 18 cm (7.1-inch) high zoneand has a mass of 11.5 kg (25 lb). It was supported by a lander, a tetrahedron-shaped structure with a mass of 250 kg (550 lb), and had a camera, scientific instrumentation, three petals of solar panels, a meteorology mast, and 6 kg (13 lb) of equipment that was neededto maintain communications between the rover and the lander. Hardware contain a steerable, high-gain X-band antenna that could send approximately 5.5 kilobits per second into a 70 m (230 ft) Deep ZoneNetwork antenna, 3.3 m2 (36 sq ft) gallium-arsenide solar arrays that generated 1.1 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.
One of the lander's main tasks was to assistancethe rover by imaging its operations and sending data from the rover to Earth. The lander had rechargeable batteries and over 2.5 m (8.2 ft) of solar cells on its petals. The lander contained a stereoscopic camera with spatial filters on an expandable pole called Photo for Mars Pathfinder (IMP), and the Atmospheric Structure Instrument/Meteorology Package (ASI/MET) which acted as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure contain three windsocks mounted at three heights on a pole, the topmost at about one meter (3.3 ft) and generally registered winds from the west. To provide continuous data, the IMP photo the windsocks once every daylight hour. These measurements permittedthe eolian processes at the landing site, including the particle threshold and the aerodynamic surface roughness, to be measured.
The square eyes of the IMP camera are separated by 15 cm (5.9 in) to provide stereoscopic vision and ranging performance to assistancerover 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 utilize as a readout spacefor the electronic shutter. The optics had an effective pixel resolution of one milliradian per pixel which gives 1 mm (0.039 in) per pixel at a range of one meter (3.3 ft). 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 plannedand built by AEC Able Engineering. The mast keep the camera at approximately 1.5 m (4.9 ft) above the Martian surface and extends Pathfinder's horizon to 3.4 km (2.1 mi) on a featureless plane.
Sojourner had solar panels and a non-rechargeable lithium-thionyl chloride (LiSOCl2) battery that could provide 150 watt-hours and permittedlimited nocturnal operations. Once the batteries were depleted, the rover could only operate during the day. The batteries also permittedthe rover's health to be checked while enclosed in the cruise stage while en route to Mars. The rover had 0.22 m2 (2.4 sq ft) of solar cells, which could produce a maximum of about 15 watts on Mars, depending on conditions. The cells were GaAs/Ge (Gallium Arsenide/Germanium) with approximately 18 percent efficiency. They could survive temperatures down to about −140 °C (−220 °F). 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.
The rover's wheels were angry of aluminum and were 13 cm (5.1 in) in diameter and 7.9 cm (3.1 in) wide. They had serrated, stainless steel tracks that could generate a pressure of 1.65 kPa (0.239 psi) in optimal conditions on soft ground. No such need arose during the operational phase. Each wheel was driven by its own independent motor. The first and third wheels were utilize for steering. A six-wheel-steering configuration was considered, but this was too heavy. As the rover rotated on itself, it drew a 74 cm (29 in) wide circle.
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. JPL's Don Bickler developed the wheels, which were referred to as "Rocker-bogie", for the experimental "Rocky" car, of which the Sojourner is the eighth version. 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 containsprings or other elastic elements, which could have increased the pressure exerted by each wheel. This system permittedthe overcoming of obstacles up to 8 cm (3.1 in) high but theoretically would have permittedthe rover to overcome obstacles of 20 cm (7.9 in), or about 30% of the rover's length. The suspension system was also given the ability to collapse on itself so the rover would occupy 18 cm (7.1 in) in the cruising configuration.
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—and was adopted with appropriate precautions in the subsequent Spirit and Opportunity rover missions.
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 the JPL in the development of car for the Moon and Mars were examined. The utilizeof 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 zonein front—the ground corresponding to the next step—leading to further difficulties. The choice of a wheeled carsolved most of the stability issue, led to a reduction in weight, and improved efficiency and control compared to the previous solution. The simplest configuration was a four-wheel system that, however, encounters difficulties in overcoming obstacles. Better solutions were the utilizeof six or eight wheels with the rear ones able to push, allowing the obstacle to be overcome. The lighter, easy, six-wheeled option was preferred.
The rover could travel 500 m (1,600 ft) from the lander—the approximate limit of its communication range— and had a maximum speed of 1 cm/s (0.39 in/s).
Sojourner's central processing unit (CPU) was an Intel 80C85 with a 2 MHz clock, addressing 64 kilobytes (Kb) of memory, and running a cyclic executive. It had four memory shop; 64 Kb of RAM angry by IBM for the main processor, 16 Kb of radiation-hardened PROM angry by Harris, 176 Kb of non-volatile storage angry by Seeq Technology, and 512 Kb of temporary data storage angry by Micron. The electronics were housed inside the rover's warm electronics box (WEB). 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. The aerogel utilize on the Sojourner had a density of approximately 20 mg/cc. This insulator was plannedto 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 −40 and 40 °C (−40 and 104 °F), while externally the rover experienced a temperature range between 0 and −110 °C (32 and −166 °F).
The mission was jeopardised by a concurrent programbug in the lander 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 computer restart caused by priority inversion. No scientific or engineering data was lost after a computer restartbut all of the following operations were interrupted until the next day. Restart occurred on July 5, 10, 11 and 14 during the mission before the programwas patched on July 21 to enable priority inheritance.
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 one-half kilometre (0.31 mi). Under normal operation, it would periodically send a "heartbeat" message to the lander. If no response was given, the rover could autonomously return to the areaat which the last heartbeat was get. If desired, the same strategy could be utilize to deliberately extend the rover's operational range beyond that of its radio transceiver, although the rover rarely traveled further than 10 meters (33 ft) from Pathfinder during its mission. The Ultra high frequency (UHF) radio modems operated in half-duplex mode, meaning they could either send or getdata but not both at the same time. The data was communicated in bursts of 2 kB.
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. Both front cameras were coupled with five laser stripe projectors that enabled stereoscopic photo to be taken along with measurements for hazard detection in the rover's path. The optics consisted of a window, lens, and field flattener. The window was angry of sapphire while the lens objective and flattener were angry of zinc selenide. A color camera with the same resolution was located on the back of the rover near the APXS, and rotated by 90°. It deliveredphoto of the APXS's target locationand the rover's ground tracks. 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. The cameras utilize CCDs manufactured by Eastman Kodak Company; they were clocked out by CPU, and capable of auto-exposure, Block Truncation Coding (BTC) data compression, poorpixel/column handling, and photodata packetizing. Because the rover's cameras had zinc-selenide lenses, which block light with a wavelength shorter than 500 nanometers (nm), no blue light actually reached the blue-and-infrared-sensitive pixels, which therefore recorded only infrared light. The rover was photo on Mars by the base station's IMP camera system, which also helped determine where the rover cango.
Sojourner operation was supported by "Rover Control Software" (RCS) that ran on a Silicon Graphics Onyx2 computer on Earth and permittedcommand 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 programpermittedthe 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 utilize as icons to presentwhere the rover cango. Desired area 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. The rover drivers were Brian K. Cooper and Jack Morrison.
The Alpha Proton X-Ray Spectrometer (APXS) was plannedto 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. The instrument had a curium-244 source that emits alpha particles 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.
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-rays upon recombination of atomic shell vacancies madeby alpha particle bombardment by interaction with the electrons of the innermost orbitals. The instrument was plannedto detect the energy of all three components of the return radiation, making it possible to identify the atoms showand their quantities in a few tens of micrometers below the surface of the analyzed sample. The detection process was rather slow; each measurement could take up to ten hours.
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 showat concentration levels above a fraction of one percent. The instrument was plannedfor the failed Russian Mars-96 mission. The alpha particle and proton detectors were deliveredby the Chemistry Department of the Max Planck Institute and the X-ray detector wad developed by the University of Chicago.
During each measurement, the front surface of the instrument had to be in contact with the sample. 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°. The dual mobility of the rover and the ADM increased the potential of the instrument—the first of its typeto reach Mars.
The Wheel Abrasion Experiment (WAE) was plannedto 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 photovoltaic sensor. The collected signal was analyzed to determine the desired information. 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. Following the WAE experiment on Mars, attempts were angry to reproduce the result observed in the laboratory.
The interpretation of the effect proposed by Ferguson et al. recommend the soil at the landing pageis angry up of fine-grained dust of limited hardness with a grain size of less than 40 µm. The instrument was developed, built and directed by the Lewis' Photovoltaics and ZoneEnvironments Branch of the Glenn Research Center.
The Content Adherence Experiment (MAE) was plannedby engineers at the Glenn Research Center to measure the everydayaccumulation of dust on the back of the rover and the reduction in the energy-conversion capacity of the photovoltaic panels. It consisted of two sensors.
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 angry, both with the glass in territoryand removed. From the comparison, it was possible to deduce the reduction in cell yield caused by the dust. Effect from the first cell were compared with those of a second photovoltaic cell that was exposed to the Martian environment. The second sensor utilize a quartz crystal microbalance (QCM) to measure the weight-per-surface unit of the dust deposited on the sensor.
During the mission, a everydayrate 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. This recommend the dust settling on the rover was suspended in the atmosphere and was not raised by the rover's movements.
Since it was established transmissions relating to driving the Sojourner occur once every sol, the rover was equipped with a computerized control system to tutorialits movements independently.
A series of commands had been programmed, providing an appropriate strategy for overcoming obstacles. One of the basiccommands 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 get from Earth a command string containing the coordinates of the arrival point, which it would have to reach autonomously.
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 findfor the signal produced by the lasers in the cameras' photo. In the case of a flat surface and no obstacles, the position of this signal was unchanged with respect to the reference signal shop in the computer; any deviation from this position angry it possible to identify the kindof obstacle. The photographic scan was performed after each advance equal to the diameter of the wheels, 13 cm (5.1 in), and before each turn.
In the confirmed presence of an obstacle, 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 freshstraight 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. The steering angle of the wheels was controlled through potentiometers.
In particularly uneven terrain, the procedure described above would have been prevented by the presence of a hugenumber of obstacles. There was, therefore, a second procedure known as "thread the needle", which consisted of proceeding between two obstacles along the bisector between them, providing they were sufficiently zone to letthe 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 freshstraight trajectory to reach the target. Conversely, the rover would have had to go back and testa different trajectory. As a last resort, contact sensors were mounted on the front and rear surfaces of the rover.
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. Three accelerometers 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°, though it was plannednot to hintover when tilted at 45°. The distance traveled was determined by the number of revolutions of the wheels.
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 in the JPL. NASA designedto send Marie Curie on the canceled Mars Surveyor 2001 mission; it was recommendedto send it in 2003, proposing Marie Curie to be deployed "using a robotic-arm attached to the lander". Rather than this, the Mars Exploration Rover softwarewas launched in 2003. In 2015, JPL transferred Marie Curie to the Smithsonian National Air and ZoneMuseum (NASM).
According to zonehistorian and NASM curator Matt Shindell:
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.
To tryrobotic prototypes and app under natural lighting conditions, JPL built a simulated Martian landscape called "Mars Yard". The trylocationmeasured 21 by 22 m (69 by 72 ft) and had a variety of terrain arrangements to assistancemultiple tryconditions. The soil was a combination of beach sand, decomposed granite, brick dust, and volcanic cinders. The rocks were several kind of basalts, including fine-grained and vesicular in both red and black. Rock-size distributions were chosento match those seen on Mars and the soil characteristics matched those found in some Martian regions. Hugerocks were not Mars-like in composition, being less dense and easier to move for testing. Other obstacles such as bricks and trenches were often utilize for specialized testing. Mars Yard was expanded in 1998 and then in 2007 to assistanceother Mars rover missions.
The name "Sojourner" was selectedfor the rover through a tournamentheld 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 selecta "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. 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.
Some 3,500 papers were get 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 champion were selectedon 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. The winning paper was written by 12-year-old Valerie Ambroise of Bridgeport, Connecticut, who recommendeddedicating the rover to Sojourner Truth, a Civil War era African-American abolitionist and women's rights advocate. The second territorywent to Deepti Rohatgi, 18, of Rockville, Maryland, who proposed Marie Curie, a Nobel Prize-winning Franco-Polish chemist. Third territorywent to Adam Sheedy, 16, of Round Rock, Texas, who chose Judith Resnik, a United States astronaut and ZoneShuttle crew member who died in the 1986 Challenger disaster. The rover was also known as Microrover Flight Experiment abbreviated MFEX.
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, from July 5 to September 27, 1997, when the lander cut off communications with Earth. In the 83 sols of activity—twelve times the expected duration for the rover—Sojourner traveled 104 m (341 ft), always remaining within 12 m (39 ft) of the lander. It collected 550 photo, performed 16 analyzes through the APXS—nine of rocks and the remainder of the soil— and performed 11 Wheel Abrasion Experiments and 14 experiments on soil mechanics in cooperation with the lander.
The landing pagefor the rover was selectedin April 1994 at the Lunar and Planetary Institute in Houston. The landing pageis 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 selectedbecause it was thought to be a relatively safe surface on which to land and one that include a wide variety of rocks that were deposited during a flood. This locationwas well-known, having been photographed by the Viking mission. After a successful landing, the lander was officially named "The Vehicle Sagan Memorial Station" in honor of the astronomer.
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.
The rocks at the landing pagewere given names of cartoon hero. 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.
The first analysis was carried out on the rock called "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" was analyzed on the 10th sol. It has been recommendedthe 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.
Both rocks turned out to be andesites; this finding surprised some scholars because andesites are formed by geological processes that require an interaction between content of the crust and the mantle. A lack of infoon the surrounding highlands angry it impossible to grasp all of the implications of the uncover.
The rover was then directed to the next target and on the 14th sol, it analyzed the rock named "Scooby-Doo" and photo the "Casper" rock. Both were deemed to be consolidated deposits. The rock called "Moe" showed evidence of victory 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.
The landing pageis rich in varied rocks, some of which are clearly volcanic in origin, such as "Yogi"; others are conglomerates, the origins of which are the topicof several proposals. In one hypothesis, they formed in the presence of water in Mars' distant past. In assistanceof this, high silicon material 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. Smaller, more rounded stones may also have been generated during a surface impact event.
When the mission's final effect were described in a series of articles in the journal Science (December 5, 1997), it was trust the rock Yogi had a coating of dust but was similar to the rock Barnacle Bill. Calculations recommendedboth 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.
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:
Some sections of this article were originally translated from the Italian Wikipedia article. For original, see .
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