HOME

TheInfoList



OR:

The robotic ''Sojourner'' rover reached
Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...
on July 4, 1997 as part of the ''
Mars Pathfinder ''Mars Pathfinder'' was an American robotic spacecraft that landed a base station with a rover (space exploration), roving probe on Mars in 1997. It consisted of a Lander (spacecraft), lander, renamed the Carl Sagan Memorial Station, and a ligh ...
'' mission. ''Sojourner'' was operational on Mars for 92 sols (95 Earth days), and was the first wheeled vehicle to operate on an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...
other than the Earth or Moon. The landing site was in the Ares Vallis channel in the Chryse Planitia region of the Oxia Palus quadrangle. 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 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 received on the morning of October 7, 1997. ''Sojourner'' traveled just over 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.


Mission

''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. 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 "faster, better, cheaper" approach embraced by the NASA administration. 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 required careful selection of the landing site to balance the technical requests with the scientific ones. 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.


Technical characteristics

''Sojourner'' was developed by NASA's
Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center (FFRDC) in La Cañada Flintridge, California, Crescenta Valley, United States. Founded in 1936 by Cali ...
(JPL). It is a six-wheeled, long, wide and high vehicle. In the mission's cruise phase, it occupied an high space and has a mass of . It was supported by a lander, a tetrahedron-shaped structure with a mass of , and had a camera, scientific instrumentation, three petals of solar panels, a
meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...
mast, and of equipment that was required to maintain communications between the rover and the lander. Hardware included a steerable, high-gain
X-band The X band is the designation for a band of frequency, frequencies in the microwave radio region of the electromagnetic spectrum. In some cases, such as in communication engineering, the frequency range of the X band is set at approximately 7.0� ...
antenna that could send approximately 5.5
kilobit The bit is the most basic unit of information in computing and digital communication. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented as ...
s per second into a
Deep Space Network The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...
antenna, 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.


Lander

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 of solar cells on its petals. The lander contained a stereoscopic camera with
spatial filter A spatial filter is an optical device which uses the principles of Fourier optics to alter the structure of a beam of light or other electromagnetic radiation, typically coherent laser light. Spatial filtering is commonly used to "clean up" the ...
s on an expandable pole called Imager 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 included three windsocks mounted at three heights on a pole, the topmost at about and generally registered winds from the west. 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. The square eyes of the IMP camera are separated by 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 A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...
(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 per pixel at a range of . 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 above the Martian surface and extends ''Pathfinder''s horizon to on a featureless plane.


Power system

''Sojourner'' had solar panels and a non-rechargeable lithium-thionyl chloride (LiSOCl2) battery that could provide 150 watt-hours and allowed limited nocturnal operations. Once the batteries were depleted, the rover could only operate during the day. The batteries also allowed the rover's health to be checked while enclosed in the cruise stage while ''en route'' to Mars. The rover had 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 . 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.


Locomotion system

The rover's wheels were made of
aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
and were in diameter and wide. They had serrated,
stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...
tracks that could generate a pressure of 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 used for steering. A six-wheel-steering configuration was considered, but this was too heavy. As the rover rotated on itself, it drew a 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" vehicles, 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 include springs or other elastic elements, which could have increased the pressure exerted by each wheel. This system allowed the overcoming of obstacles up to high but theoretically would have allowed the rover to overcome obstacles of , 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 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 JPL in the development of vehicles for the Moon and Mars were examined. 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. 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. 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. The rover could travel from the lander—the approximate limit of its communication range— and had a maximum speed of .


Hardware and software

''Sojourners
central processing unit A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
(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 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). The WEB is a box-like structure formed from
fiberglass Fiberglass (American English) or fibreglass (English in the Commonwealth of Nations, Commonwealth English) is a common type of fibre-reinforced plastic, fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened i ...
facesheets bonded to aluminum spars. The gaps between facesheets were filled with blocks of
aerogel Aerogels are a class of manufacturing, synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas, without significant collapse of the gel structure. The result is a solid wit ...
that worked as
thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...
. The aerogel used on the ''Sojourner'' had a density of approximately 20 mg/cc. 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 , while externally the rover experienced a temperature range between . The ''Pathfinder'' lander's computer was a Radiation Hardened IBM Risc 6000 Single Chip with a Rad6000 SC CPU, 128 megabytes (Mb) of RAM and 6 Mb of
EEPROM EEPROM or E2PROM (electrically erasable programmable read-only memory) is a type of non-volatile memory. It is used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a separate chip d ...
memory, and its
operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...
was
VxWorks VxWorks is a real-time operating system (or RTOS) developed as proprietary software by Wind River Systems, a subsidiary of Aptiv. First released in 1987, VxWorks is designed for use in embedded systems requiring real-time, Deterministic system, ...
. The mission was jeopardised by a concurrent software bug 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 resets caused by
priority inversion In computer science, priority inversion is a scenario in scheduling in which a high-priority task is indirectly superseded by a lower-priority task, effectively inverting the assigned priorities of the tasks. This violates the priority model tha ...
. No scientific or engineering data was lost after a computer reset but all of the following operations were interrupted until the next day. Resets occurred on July 5, 10, 11 and 14 during the mission before the software was patched on July 21 to enable priority inheritance.


Communication and cameras

''Sojourner'' communicated with its base station using a 9,600
baud In telecommunications and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
radio modem, although error-checking protocols limited communications to a functional rate of 2,400 baud with a theoretical range of about . 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 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 from ''Pathfinder'' during its mission. The
Ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...
(UHF) radio modems operated in
half-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...
mode, meaning they could either send or receive data but not both at the same time. The data was communicated in bursts of 2 kB. The rover was imaged on Mars by the base station's IMP camera system, which also helped determine where the rover should go. 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 In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compressi ...
, bad pixel/column handling, and image data packetizing. Both front cameras were coupled with five
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
stripe projectors that enabled
stereoscopic Stereoscopy, also called stereoscopics or stereo imaging, is a technique for creating or enhancing the illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is ...
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. The window was made of
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name ''sapphire ...
while the lens objective and flattener were made of zinc selenide. 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. 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 Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
and blue light. Because the rover's cameras had zinc-selenide lenses, which block light with a
wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
shorter than 500 nanometers (nm), no blue light actually reached the blue-and-infrared-sensitive pixels, which therefore recorded only infrared light.


Rover Control Software

''Sojourner'' operation was supported by "Rover Control Software" (RCS) that ran on a 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. The rover drivers were Brian K. Cooper and Jack Morrison. 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


Science payload


Alpha Proton X-Ray Spectrometer

The Alpha Proton X-Ray
Spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...
(APXS) was designed to determine the
chemical composition A chemical composition specifies the identity, arrangement, and ratio of the chemical elements making up a compound by way of chemical and atomic bonds. Chemical formulas can be used to describe the relative amounts of elements present in a com ...
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 particle Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay but may also be produce ...
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. The principle of the APXS technique is based on the interaction of alpha particles from a
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...
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 An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s upon recombination of atomic shell vacancies created by alpha particle bombardment by interaction with the electrons of the innermost orbitals. 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. 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 Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
and
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
,
proton emission Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a atomic nucleus, nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay ...
is mainly sensitive to
sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
,
magnesium Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
,
aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
,
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
,
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
, and X-ray emission is more sensitive to heavier elements
sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
to
iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
and beyond. Combining all three measurements makes APXS sensitive to all elements with the exception of
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
that is present at concentration levels above a fraction of one percent. The instrument was designed for the failed Russian Mars-96 mission. 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 The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...
. 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 A robotic arm is a type of mechanical arm, usually programmable, with similar functions to a human arm; the arm may be the sum total of the mechanism or may be part of a more complex robot. The links of such a manipulator are connected by join ...
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 kind to reach Mars.


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 The angstrom (; ) is a unit of length equal to m; that is, one ten- billionth of a metre, a hundred-millionth of a centimetre, 0.1 nanometre, or 100 picometres. The unit is named after the Swedish physicist Anders Jonas Ångström (1814� ...
, 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 made to reproduce the effects observed in the laboratory. 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 μm. The instrument was developed, built and directed by the Lewis' Photovoltaics and Space Environments Branch of the
Glenn Research Center NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park, Ohio, Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a s ...
.


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. 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 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. Results from the first cell were compared with those of a second photovoltaic cell that was exposed to the Martian environment. The second sensor used a quartz crystal microbalance (QCM) to measure the weight-per-surface unit of the dust deposited on the sensor. 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. This suggests the dust settling on the rover was suspended in the atmosphere and was not raised by the rover's movements.


Control system

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. 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. 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. The photographic scan was performed after each advance equal to the diameter of the wheels, , 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 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. The steering angle of the wheels was controlled through
potentiometer A potentiometer is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrum ...
s. 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 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. 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 A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining Orientation (geometry), orientation and angular velocity. It is a spinning wheel or disc in ...
. Three
accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...
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°, though it was designed not to tip over when tilted at 45°. The distance traveled was determined by the number of revolutions of the wheels.


''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. 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". Rather than this, the
Mars Exploration Rover NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, ''Spirit (rover), Spirit'' and ''Opportunity (rover), Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rove ...
program was launched in 2003. In 2015, JPL transferred ''Marie Curie'' to the
Smithsonian National Air and Space Museum The National Air and Space Museum (NASM) of the Smithsonian Institution is a museum in Washington, D.C., in the United States, dedicated to human flight and space exploration. Established in 1946 as the National Air Museum, its main building ...
(NASM). According to space historian and NASM curator Matt Shindell:


Mars Yard

To test robotic prototypes and applications under natural lighting conditions, JPL built a simulated Martian landscape called "Mars Yard". The test area measured 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. Mars Yard was expanded in 1998 and then in 2007 to support other Mars rover missions.


Naming

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. 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 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. The winning paper was written by 12-year-old Valerie Ambroise of Bridgeport, Connecticut, who suggested dedicating the rover to Sojourner Truth, a Civil War era African-American
abolitionist Abolitionism, or the abolitionist movement, is the political movement to end slavery and liberate enslaved individuals around the world. The first country to fully outlaw slavery was Kingdom of France, France in 1315, but it was later used ...
and women's rights advocate. The second place went to Deepti Rohatgi, 18, of
Rockville, Maryland Rockville is a city in and the county seat of Montgomery County, Maryland, United States, and is part of the Washington metropolitan area. The 2020 United States census, 2020 census tabulated Rockville's population at 67,117, making it the fourth ...
, who proposed
Marie Curie Maria Salomea Skłodowska-Curie (; ; 7 November 1867 – 4 July 1934), known simply as Marie Curie ( ; ), was a Polish and naturalised-French physicist and chemist who conducted pioneering research on radioactivity. She was List of female ...
, a Nobel Prize-winning Polish-French chemist. Third place went to Adam Sheedy, 16, of Round Rock, Texas, who chose Judith Resnik, a United States astronaut and
Space Shuttle The Space Shuttle is a retired, partially reusable launch system, reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. ...
crew member who died in the 1986 ''Challenger'' disaster. The rover was also known as ''Microrover Flight Experiment'' abbreviated MFEX.


Operations

''Sojourner'' was launched on December 4, 1996, aboard a
Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas, and sometimes known as the Thorad Delta 1. Delta II was part of the Delta rocket family, derived directly from the Delta 3000, and entered service in ...
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 , always remaining within of the lander. It collected 550 images, 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.


Landing site

The landing site for the rover was chosen in April 1994 at the
Lunar and Planetary Institute The Lunar and Planetary Institute (LPI) is a scientific research institute dedicated to study of the Solar System, its formation, evolution, and current state. The Institute is part of the Universities Space Research Association (USRA) and is ...
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 Vikings were seafaring people originally from Scandinavia (present-day Denmark, Norway, and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded, and settled throughout parts of Europe.Roesdahl, pp. 9� ...
'' mission. After a successful landing, the lander was officially named "The
Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist and science communicator. His best known scientific contribution is his research on the possibility of extraterrestrial life, including e ...
Memorial Station" in honor of the astronomer.


Deployment

''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.


Rock analysis

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. 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 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. Both rocks turned out to be
andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...
s; this finding surprised some scholars because andesites are formed by geological processes that require an interaction between materials of the crust and the mantle. A lack of information on the surrounding highlands made it impossible to grasp all of the implications of the discovery. 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. Both were deemed to be consolidated deposits. The rock called "Moe" showed evidence of
wind erosion Aeolian processes, also spelled eolian, pertain to wind activity in the study of geology and weather and specifically to the wind's ability to shape the surface of the Earth (or other planets). Winds may erode, transport, and deposit material ...
. Most of the rocks analyzed showed a high
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
content. In a region nicknamed "Rock Garden", the rover encountered crescent-moon-shaped dunes that are similar to dunes on earth. The landing site is rich in varied rocks, some of which are clearly volcanic in origin, such as "Yogi"; others are 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. In support of this, high silicon contents would be detected. This could also be a consequence of
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...
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 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 Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...
,
ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printi ...
,
iron sulfide Iron sulfide or iron sulphide can refer to range of chemical compounds composed of iron and sulfur. Minerals By increasing order of stability: * Iron(II) sulfide, FeS * Greigite, Fe3S4 (cubic) * Pyrrhotite, Fe1−xS (where x = 0 to 0.2) (monocli ...
, and calcium phosphate.


''Sojourner'' in popular culture

* In the 2000 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. * In the opening titles of the 2001 '' 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''. 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'', and the 2015 film based on it, 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." In the movie, Mark Watney is later seen in his Mars outpost, the Ares III Hab, with the ''Sojourner'' roving around.


Awards and honors

* On October 21, 1997, at the
Geological Society of America The Geological Society of America (GSA) is a nonprofit organization dedicated to the advancement of the geosciences. History The society was founded in Ithaca, New York, in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hi ...
's annual meeting in
Salt Lake City, Utah Salt Lake City, often shortened to Salt Lake or SLC, is the List of capitals in the United States, capital and List of cities and towns in Utah, most populous city of the U.S. state of Utah. It is the county seat of Salt Lake County, Utah, Salt ...
, ''Sojourner'' was awarded honorary membership in the Society's Planetary Geology Division. * In November 1997, to commemorate the achievements of
Mars Pathfinder ''Mars Pathfinder'' was an American robotic spacecraft that landed a base station with a rover (space exploration), roving probe on Mars in 1997. It consisted of a Lander (spacecraft), lander, renamed the Carl Sagan Memorial Station, and a ligh ...
program, a $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. * ''Sojourner'' was included in the Robot Hall of Fame by
Carnegie Mellon University Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania, United States. The institution was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools. In 1912, it became the Carnegie Institu ...
. * '' 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.


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: * Project Manager: Tony Spear, JPL * 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 Peter Hopkinson Smith (born January 17, 1940) is a scholar of Latin American history, politics, economics, and diplomacy. He is a distinguished Professor Emeritus of Political Science and the Simon Bolivar Professor of Latin American Studies a ...
,
University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a Public university, public Land-grant university, land-grant research university in Tucson, Arizona, United States. Founded in 1885 by the 13th Arizona Territorial Legislature, it ...
* 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 The Max Planck Society for the Advancement of Science (; abbreviated MPG) is a formally independent non-governmental and non-profit association of German research institutes. Founded in 1911 as the Kaiser Wilhelm Society, it was renamed to the M ...
, 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

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. File:PIA01551.jpg, The sol 2 "insurance panorama" of ''Sojourner'', taken on 530, 600, and 750 nm filters. 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.


Comparison to later Mars rovers

File:H rover-comp wheels 02.jpg File:Mars rovers wheels nested.jpg File:Mars wheels compared to 14inch disk.jpg


See also

*
Exploration of Mars The planet Mars has been explored remotely by spacecraft. Uncrewed spacecraft, Probes sent from Earth, beginning in the late 20th century, have yielded a large increase in knowledge about the Martian system, focused primarily on understanding G ...
* ''Mars 3'' (lander) * ''Viking 1'' (lander) * ''Viking 2'' (lander) * ''Spirit'' (rover) * ''Opportunity'' (rover) * ''Curiosity'' (rover) * ''Perseverance'' (rover) * ''Zhurong'' (rover) * ''Rosalind Franklin'' (rover) (planned mission) * Comparison of embedded computer systems on board the Mars rovers


Footnotes


References

Some sections of this article were originally translated from the Italian Wikipedia article. For original, see :it:Sojourner.


Further reading

* *


External links

* * *
Mars Microrover Photo GalleryHow The Age Of Mars Rovers Began
by Lauren J. Young on
Science Friday ''Science Friday'' (known as ''SciFri'' for short) is a weekly call-in talk show that broadcasts each Friday on public radio stations, distributed by WNYC Studios, and carried on over 500 public radio stations. ''SciFri'' is hosted by science ...

''Mars Pathfinder'' Media Reel
by JPL on YouTube
Sojourner Patent
Mars Pathfinder Mars rovers Derelict landers (spacecraft) Attached spacecraft Spacecraft launched in 1996 Soft landings on Mars Robots of the United States 1996 robots 1996 in the United States Six-wheeled robots 1997 on Mars Mars robots {{Good article