Mars Exploration Rover
The Mars Exploration Rover Mission 2003 (MER) was a NASA space mission that began in 2003 with the launch of two launch vehicles to transport two rovers - Spirit and Opportunity - to explore the surface and geology of Mars . The mission was part of NASA's Mars exploration program, which already includes three successful space probes: The two Viking Landers from 1976 and Pathfinder from 1997.
The aim of the mission was to drop two automatic off-road vehicles (English rover ) independently of each other on Mars, to research the geological conditions there and to look for evidence of water, the presence of which is considered a basic requirement for life on Mars . Each rover itself was solar powered and equipped with instruments to photograph the surface of Mars and analyze stones. Due to the distance to earth, direct control of the rovers was not possible, so the software control of the vehicles was intelligent enough to automatically approach targets and avoid obstacles. Although the mission was only designed for 90 sols (Martian days), Opportunity worked until June 12, 2018 (5111 sols). Spirit's mission was declared completed on May 25, 2011 after the rover went into hibernation in March 2010. For the first time, it was possible to prove directly on site that liquid water deposits also existed on other planets and for the first time sedimentary rocks of a foreign planet were examined. For the first time, the data from the exploration of a strange celestial body was made publicly accessible almost in real time via the Internet , even before the project participants could evaluate it themselves.
The mission was maintained for NASA by the Jet Propulsion Laboratory , which planned, built and operated the rovers. German researchers were also represented with two instruments on board: a Mössbauer spectrometer from Johannes Gutenberg University Mainz and an alpha particle X-ray spectrometer from the Max Planck Institute for Chemistry in Mainz .
The first ideas for this Mars mission came from a group of scientists around Steve Squyres in the early 1990s . A Mars lander should collect geological information about Mars using a set of instruments. One package consisted of a stereo camera , several spectrometers and a microscope . With this payload (named "Athena" after the Greek patron goddess of science) the lander should be able to perform tasks similar to those of a geologist on earth. A first mission was supposed to start in 1995, but was rejected by NASA.
With the NASA program “better, faster, cheaper”, the scientific payload was then to be brought to Mars in a highly restricted manner on a rover. However, after the Mars probes Mars Climate Orbiter and Mars Polar Lander did not reach the planet, development for this mission was also stopped again. Due to the previous loss of two probes, NASA was now under great pressure to succeed. Only after a restructuring of NASA was the mission restarted in 2000, especially in order not to miss the unique start date of 2003: In this year Mars and Earth came closer than they have been in 60,000 years. Therefore a Martian rocket could reach Mars with less energy, or more payload could be transported with the same energy. In addition, the then NASA boss Daniel Goldin decided that two Mars rovers should be sent at the same time. This redundancy halved the risk and doubled the potential scientific yield. However, this also meant the double work of sending the two rovers on their way to Mars within three years.
NASA defined the following seven scientific goals that it hoped to achieve with the Mars Exploration Rovers:
- Look for stones and soil that contain evidence of previous water activity. In particular, samples are sought that contain minerals that have been created by processes influenced by water such as precipitation , evaporation , sedimentation or hydrothermal processes .
- Determination of the distribution and composition of minerals, rocks and soils around the landing site.
- Determination of the geological processes that shaped the surrounding landscape and shaped its chemistry. Such processes could be water or wind erosion, sedimentation, hydrothermal mechanisms, volcanism or crater formation.
- Carrying out calibration and validation of surface observations made with instruments from probes in Mars orbit. This allows the accuracy and effectiveness of the remote observation instruments to be determined from Mars orbit.
- Search for ferrous minerals, identify and quantify the relative proportions of mineral types that contain water or have been formed in water, such as ferrous carbonates .
- Characterization of the mineralogy and surface properties of stones and soils and determination of the processes that shaped them.
- Look for geological clues about the environmental conditions that existed when liquid water was present. Assess whether this environment could help bring about life.
Selection of the landing site
During the construction of the rovers, scientists and engineers compiled a list of 155 candidates for landing sites within two years, using images from the Mars Global Surveyor and Mars Odyssey Orbiter. According to NASA's “follow the water” strategy, locations were selected that show evidence of the former influence of water. In addition to the scientific objectives, technical boundary conditions also had to be complied with in order to guarantee a safe landing. The landing site had to be near the Martian equator because of the solar cells . In order for the parachute to function optimally during landing, the landing site had to be at least 1.3 km lower than the normal Mars level due to the atmospheric pressure. In addition, strong winds were not allowed to prevail and the area was not allowed to be too stony or have too great differences in altitude.
NASA chose Gusev Crater as the landing site for Spirit . This has a diameter of 166 km and shows traces of a former lake. A wide and now dry valley called Ma'adim Vallis leads over 900 km to the crater and seems to have been formed by flowing water. The water cut into the rim of the crater and filled a large part of the crater. Sediments could therefore be found on the bottom of the Gusev crater, which have preserved these conditions. A problem with this area was high winds that could affect landing. NASA took the increased risk, however, because they estimated the expected scientific yield here to be very high.
Opportunity should land on the Meridiani Planum plane, which is on the opposite side of Mars. The orbiters had found indications that water once existed here in the past . An instrument from the Mars Global Surveyor found gray hematite here, which mostly forms in the presence of liquid water.
Takeoff and flight
The launch vehicle for the two space probes was a three-stage Delta II of the type 7925 with a total height of 39.6 meters. The first stage was operated with liquid fuel . This stage generated a thrust of 890,000 Newtons, reinforced by 440,000 Newtons (Spirit) or 550,000 Newtons (Opportunity) additional thrust from nine solid rocket rockets . The second stage also used liquid fuel, was re-ignitable, and delivered 44,000 Newtons of thrust. The third stage had a solid propulsion system, which delivered a final thrust of 66,000 Newtons for the way to Mars.
Spirit was launched on June 10, 2003, 17:59 UTC from Launch Complex 17A at Cape Canaveral Air Force Station with a Delta-II-7925, Opportunity took off from Launch Complex 17B on July 7, 2003, 15:18 UTC with a slightly more powerful Delta-II-7925H missile.
The flight stage was the component used in the journey from Earth to Mars. It had a diameter of 2.65 meters and was 1.60 meters high. The main structure was made of aluminum with an outer ring of ribs covered by solar cells. These were divided into five sections and delivered between 600 W (near the earth) to 300 W (near Mars). The internal electronics were kept warm by heaters and multiple insulation. A cooling system with freon led the waste heat from the flight computer and the communication electronics inside the rover to the outside so that they do not overheat. During the flight, the spacecraft was stabilized at two revolutions per minute . The time of the flight was used to test the equipment and software and to prepare for the arrival on Mars.
A star scanner and a sun sensor allowed the spacecraft to determine its orientation in space by determining the positions of the sun and other stars. During the flight, the spacecraft could deviate slightly off course. Therefore, six course corrections were planned in which the systems were then also checked. To correct course, it had two hydrazine tanks with 31 kg of fuel. With the help of the navigation and control systems, the spacecraft could be kept on course. For flight tracking, two traditional location methods were combined with a newer triangulation method to improve navigation precision. One of the traditional methods was ranging, which determines the distance to the spacecraft by precisely measuring the signal propagation time. The measurement of the Doppler shift of the radio signal for speed measurement was used as the second method. The new Delta-DOR (Delta - Differential One-Way Range) method added information about the location of the spacecraft perpendicular to the line of sight. Two pairs of antennas from the Deep Space Network on two different continents received signals from the probe at the same time. Thereafter, the same antennas were used to observe natural sources of radio waves whose position in the sky is known, such as quasars . By using this method, the desired landing location could be targeted more precisely than previously possible.
The spacecraft used the high frequency X-band to communicate during flight . The navigators sent commands through two antennas on the flight level: a low- gain antenna was used for communication near the earth and a medium- gain antenna at a greater distance from the earth. The low-gain antenna was omnidirectional, so that the radiated power that reaches the earth drops sharply with increasing distance. At greater distances, the mean gain antenna was used, which sends the signals in a focused beam towards the earth.
After airbags had been successfully used for the first time when the Mars Pathfinder landed, the Mars Exploration Rover was also supposed to land in the same way: First the spacecraft with the heat shield was braked in the Martian atmosphere, then the parachute was opened. Shortly before the surface of Mars, missiles stopped the probe completely, then airbags were inflated around the lander, after which the lander was lowered in free fall to the surface. After he had come to rest, the airbags were retracted and the rover contained therein was able to start its work.
The heat shields also served as protection for the lander during the seven-month journey to Mars. The front heat shield protected the lander from the intense heat development as it entered the thin Martian atmosphere. The rear heat shield contained the parachute, the electronic control for the landing process and rockets to slow down the lander at a height of 10 to 15 meters above the Martian surface and to stop any sideways movement. The heat protection shield was made of aluminum in a sandwich honeycomb construction . The outside was covered with a honeycomb phenolic resin structure. This structure was filled with a heat absorbing material. This consisted of a mixture of cork, binder and small silica glass beads. The material dissipates the heat generated by friction in the atmosphere, thereby protecting the capsule. This technique was already used in the Viking Lander missions.
The design of the parachute was based on experiences from the Viking and Pathfinder missions. During the opening, the parachute had to withstand a force of over 80,000 Newtons. It had a diameter of 14.1 meters and was made of polyester and nylon . Several problems arose during the development of the parachute. For example, it failed a test drop from a helicopter or it only opened partially. These errors could be corrected by enlarging the opening in the middle of the screen. The space available on the spacecraft for the parachute is so small that the parachute had to be packed with a special device under high pressure.
The same airbags were used for the Mars Exploration Rover mission as for the Mars Pathfinder in 1997. These airbags, manufactured by ILC Dover (which also developed the spacesuits and other technology for NASA) had to be strong enough to get the lander in front cushion the impact on stone or rough terrain and perform several jumps on the surface at high speed. In addition, the airbags had to be inflated seconds before the impact and deflated again after the safe landing. The airbags are made of Vectran , which is twice as thick as other synthetic materials such as Kevlar and which adapts better to low temperatures. In several tests it was found that the airbags could not withstand the higher loads due to the additional mass (compared to the previous model 1997) and tore. The engineers therefore reinforced the airbag fabrics, which can withstand impact with stones and the like at high speeds. Each rover had four airbags, which consisted of six interconnected chambers. These connections distributed and dampened the forces that occur upon landing. The fabric of the airbags was not attached directly to the rover, but was lashed to the lander with crossed ropes. These ropes gave the airbags the correct shape to make inflating easier. During the flight, the airbags were stowed together with three gas generators that were used to inflate them.
The spacecraft's lander was a capsule that housed the rover and protected it with the help of airbags during the impact. The lander itself had a lightweight structure consisting of a triangular base and three “petals” that gave it the shape of a tetrahedron. This structure was made of carbon fiber reinforced plastic . The rover itself was held in place inside the lander with bolts and special grooves that were removed by a small explosive charge after landing. The three leaves were connected to the base by a hinge. Each blade joint had a motor powerful enough to lift the weight of the entire lander. This made it possible for the lander to bring the rover into an upright position in any case, regardless of which side the lander came to rest on after the many jumps and turns on the surface of Mars. This wasn't necessary with Spirit, but with Opportunity. The rover contained sensors to determine the correct orientation to the surface based on the force of gravity and then to open the leaf first so that the rover was placed vertically. After this was done, the other two side panels were opened. The base plate was aligned horizontally, even if the lander had landed on larger stones.
After landing, the rover had to be able to safely exit the lander without its wheels getting caught in the airbag material. To aid in this process, the sheets included a device that would slowly pull the airbags back toward the lander so they wouldn't jam the rover. This happened even before the leaves were opened. In addition, small ramps (made of polyester fabric "Vectran") were attached to the side surfaces, which spread out and thus formed a surface that filled the large space between the leaves and bridged any unevenness. These fabric surfaces thus formed a circular area over which the rover could drive off the lander.
The entry, descent, and landing phases began when the probe reached the entry point into the Martian atmosphere, which was 3,522.2 kilometers from the center of Mars. During this phase, communication took place via the low-gain antennas mounted on the protective shield and on the rover itself. This was necessary because the probe with the heat shield was turned in the direction of flight and therefore no antenna could be aligned with the earth. In this six-minute phase, a total of 36 ten-second tones were sent to earth. The landing phase could be followed using these tones. In the event of failure, this could provide important information about the cause of the error.
First, the lander was separated from the flight stage. The lander then grazed the Martian atmosphere at a speed of 19,200 km / h or 5.4 km / s. The outside of the heat shield heated up to 1477 ° Celsius. Within four minutes, the spacecraft was braked to 1,600 km / h (0.4 km / s) by the heat shield. It was now 9.1 kilometers above the surface and the parachute was deployed. After twenty seconds, the heat shield was thrown off because it was no longer needed. Ten more seconds later, at an altitude of 6 km, the lander separated from the rear shield and was lowered on a 20-meter rope. At a height of 2.4 kilometers, the actual altitude and rate of descent were determined using the lander's radar system. Through these measurements, the landing system was able to determine how long the brake rockets had to be ignited to stop the lander. During the radar measurements, a camera ( descent imager ) took three images of the surface and thereby determined the horizontal speed of the lander.
The airbags were deployed at a height of 284 meters. Now the three brake rockets were ignited so that the lander, packed in the airbags, came to a stop at a height of 10 meters. The connecting rope was now cut and the lander fell to the surface. The lander with the airbags now hopped a few hundred meters above the surface of Mars until it came to rest.
Structure of the rover
In contrast to Mars Pathfinder , a rover did not have a fixed ground station, but all functions were integrated in the rover. It was 1.6 meters long, up to 1.5 meters high and weighed 185 kilograms. According to the specification, it should be able to travel around 100 m per day, a total of around 3 kilometers, depending on the surface properties, and remain operational on the planet's surface for up to six months. This exceeded the capabilities of its predecessor Sojourner from the Pathfinder mission in 1997 about a factor of 60. The rover was even by NASA as "robotic geologist" ( robotic geologist called) and had six independently driven wheels on stilts shaped telescopic legs.
Each rover was six wheels from aluminum equipped, each 26 cm in diameter, as in previous Mars missions of electric motors from the Swiss manufacturer Maxon Motor were driven. The specially developed chassis ( rocker bogie ) managed without springs and made it possible to roll over stones that were higher than the diameter of a wheel without losing balance. The center of gravity of the rover was exactly on the axis of the chassis. This allowed the vehicle to tilt up to 45 °, but the software prevented tilts of more than 30 °. An additional inertia measuring system determined the inclination of the rover and helped to make precise movements.
The rover reached a top speed of 5 centimeters per second on flat ground. To ensure a safe journey, the hazard avoidance software stopped the rover every 10 seconds, then checked the area within 20 seconds, and then drove again for 10 seconds. As a result, an average speed of around one centimeter per second was achieved. A distance of 600 to 1000 meters was planned for the primary mission, Opportunity reached 811 meters in these 90 sols, Spirit over 600 meters.
Opportunity covered the record distance of 220 meters on Sol 410 (March 20, 2005). By the end of his mission, Spirit had covered a distance of 7730 meters. Opportunity drove a distance of 45.16 km until June 10, 2018.
Each rover had, through its instruments, capabilities that enabled it to search its surroundings for interesting stones and soil like a geologist on Earth and to determine their composition and structure. Spirit and Opportunity each had the same set of tools:
- A panorama camera (PanCam, from JPL)
- An infrared spectrometer ("Miniature thermal emission spectrometer", Mini-TES, from Arizona State University , Tempe)
- A Mößbauer spectrometer (from Johannes Gutenberg University Mainz )
- An alpha particle X-ray spectrometer (APXS) (from the Max Planck Institute for Chemistry in Mainz)
- A microscope camera (from JPL)
These instruments were supported by the "Rock Abrasion Tool" (RAT) from Honeybee Robotics, New York. This tool was practically the “ geologist's hammer ” of the rovers, because it could remove a few millimeters of the weathered surfaces of stones in order to then examine the layers below. The tool was able to expose an area 4.5 cm in diameter and drill to a depth of five millimeters. The RAT was attached with the microscope camera, the APXS and the Mössbauer spectrometer at the end of a robotic arm (developed by Alliance Spacesystems, Pasadena). The RAT contained a cover plate made from remains from the 2001 World Trade Center collapse in New York.
The Martian dust is very magnetic. This dust was captured by magnetic surfaces (developed by the Niels Bohr Institute in Copenhagen, Denmark) in order to examine samples from it. Magnetic minerals in dust grains could be freeze-dried remains from Mars' water-rich past. A periodic examination of these particles and their accumulation patterns on the magnets could provide clues about their composition. The RAT also carried magnets to collect and study the dust on the stone surfaces. A second set of magnets was attached to the front of the rover to collect flying dust and analyze it with the Mössbauer spectrometer and the APXS. A third magnet was mounted on the rover deck and could be photographed with the panorama camera.
This high-resolution stereo camera displayed the surrounding terrain for each new location and thus provided the geological context for investigations. The two lenses were 30 centimeters apart and sat on a mast at 1.50 meters above the ground. The instrument had 14 different filters with which not only color images could be recorded, but also spectral analyzes of minerals and the atmosphere could be made. These images helped to select stones and soils as study targets and to define new travel targets for the rovers.
Miniature Thermal Emission Spectrometer
The MiniTES showed the environment in the infrared wave range and served to identify minerals on site. Investigations in the infrared range made it possible to see through the dust that covered everything in order to identify carbonates, silicates, organic molecules and minerals formed in water. It was also possible to estimate how stones and floors hold the heat within a Martian day. One goal was the search for characteristic minerals that were formed under the influence of water. The data from this instrument and panoramic camera were used to select scientific targets and explore new regions. It was also used to determine a high-resolution temperature profile of the Martian atmosphere. These data complemented the data collected by the Mars Global Surveyor Orbiter.
The Mössbauer spectrometer was used to identify iron-containing minerals. It was attached to the robot arm and was held on stones or on the ground. It identified ferrous minerals and thereby helped scientists to find out what role water had played in the creation of the objects under study and to what extent stones had weathered. It was also able to identify minerals that had formed in a hot, watery environment and that might have retained evidence of past life. The instrument used two Cobalt 57 sources to calibrate its measurements. It was a scaled down version of spectrometers that geologists use to examine rocks and soils on Earth. Since cobalt 57 has a half-life of 271 days, investigations have now taken considerably longer than during the primary mission. The spectrometer could also determine the magnetic properties of surfaces.
Alpha Particle X-Ray Spectrometer
The composition of stones was determined with the APXS . This instrument was an upgraded version of the device used by the Pathfinder mission's Sojourner rover. It was constructed in a manner similar to instruments used in geological laboratories on Earth. It used Curium 244 to measure the concentration of the key elements (other than hydrogen) that make up stones and soils. This makes it possible to determine the origin of the samples and how they have changed over time.
The microscope camera was able to take extreme close-ups of objects with a resolution of a few hundred micrometers and thus provide a context for interpreting the data on minerals and elements. With it, the finely structured properties of stones and soils could be examined. These small structures gave important clues as to how stones and soils were shaped. For example, the size and arrangement of particles in sediments could determine how they were transported and deposited. This camera provided close-ups of it to investigate these processes.
The wheels of the rovers could also serve as tools: They were moved individually and could therefore also be used as scrapers to dig up the ground and thus examine a few centimeters of the soil profile mechanically and photographically.
To calibrate the panorama camera, a kind of " sundial " was used, which was mounted on the top of the rover. This object was used to make corrections to the recorded images. At the corners of the sundial there were colored surfaces with which the colors of the Mars images could be calibrated.
Each rover had a low gain and a high gain antenna. The low gain antenna was omnidirectional and transmitted the data at a low rate to the deep space network antennas on earth. These antennas were also used to communicate with the probes in orbit around Mars, such as Mars Odyssey and (until it failed) the Mars Global Surveyor . The high gain antenna was directional, controllable and could transmit the data to earth at a higher rate. Communication could also take place via ESA's Mars Express Orbiter or the Mars Reconnaissance Orbiter . The orbiters forwarded the data to and from Earth, most of the data to Earth was passed on via Odyssey.
The transmission via the orbiters had the advantage that they are closer to the rover antennas than the earth and therefore less energy was required. In addition, the orbiters were within sight of the earth longer than the rovers. The orbiters communicated with the rovers through a UHF antenna, which had a shorter range than the low-gain and high-gain antennas. In direct communication with earth, the transmission rate was between 3,500 and 12,000 bits per second. The transmission rate to the orbiters was a constant 128,000 bits per second. An orbiter was within sight of the rover for about eight minutes per sol during the overflight. During this time, around 60 megabits of data were transferred. In the case of direct transmission to earth, the transmission of this amount of data would take between one and a half and five hours. However, due to restrictions in the energy supply, the rovers were only able to transmit just under three hours of data to Earth per day.
The power supply came from solar panels, which covered the entire top of the rover and had an area of 1.3 m 2 . In order to maximize the available space, the panels were mounted on their own wings, which were folded out after landing.
The solar cells made of gallium arsenide were arranged in three layers in order to optimize the energy yield. They delivered an energy of 900 watt hours per Martian day. At the end of the primary mission it was expected that only 600 watt hours would be available because dust settles on the cells and the season also changes. Actually, based on the experience of the Pathfinder mission, the planning had assumed that a layer of dust would deposit on the solar cells over time and that the power supply would break off after a few months. However, the atmosphere was not as dusty as expected (in Meridiani Planum) or the solar cells were unexpectedly cleaned by dust devils and gusts of wind, whereby they provided almost as much electricity as at the beginning of the mission. During operation, the angle to the sun also had to be taken into account, which changes depending on the season and the inclination of the rover (e.g. on mountain slopes). The energy gained was stored in two lithium-ion accumulators with a capacity of 8 ampere hours each.
In addition to the scientific cameras, each rover had six more to help the rover move. There were four HazCams ( Hazard Avoidance Cameras ) and two navigation cameras .
The HazCams were attached in pairs in the lower area of the front and rear of the rover. With these black and white cameras, a three-dimensional image of the surroundings could be created. This enabled the rover to avoid obstacles in conjunction with the software. The cameras had a viewing angle of 120 °. With them, the area could be surveyed up to a distance of three meters.
The navigation camera was attached to the instrument mast. With this a three-dimensional image of the surroundings could be generated. The NavCam consisted of two cameras at a distance of 30 cm, each with a viewing angle of 45 °. With these images, the scientists and engineers on Earth were able to work out a plan for the navigation of the rover. The cameras worked in conjunction with the HazCams by providing a complementary view of the surrounding landscape. With these cameras, the rover was able to move independently and avoid obstacles without waiting for commands from Earth.
During a Martian day, the temperature can differ by 113 degrees Celsius. However, the rover's electronics only worked in a temperature range of −40 to +40 degrees Celsius. That is why the most important parts such as batteries, electronics and computers are packed in an insulated box inside the rover, the Warm Electronics Box (WEB). A gold coating on the outside, airgel insulation and heating elements kept the inside of the rover warm. Excess heat was given off via radiators. Eight radioisotope heating elements provided basic heat. Each element produced one watt of heat and contains 2.7 grams of plutonium dioxide in a small capsule. These components ensured that the rover did not freeze in the cold climate of Mars.
Each rover's computer had a 32-bit Rad 6000 microprocessor , a version of the PowerPC chip used in older Macintosh computers. However, this variant was specially hardened against radiation and has already been used in many space missions. The processor operated at a rate of 20 million instructions per second. The computer memory consisted of 128 MiByte RAM , supplemented by 256 MiByte flash memory . There were also some smaller areas of non-volatile memory that was used to store data for the system without a power supply. The computer used the real-time operating system VxWorks from WindRiver, which occupies 2 megabytes of memory. The rest of the control software was 30 megabytes in size. The software itself was regularly developed to fix bugs or to improve the autonomy of the rovers when driving.
The computer was also responsible for image processing. The high-quality recordings from the PanCam cameras had to be compressed for data transmission, since larger images also require more valuable transmission time. The ICER image compression developed at JPL was based on wavelets and reduced images from 12 megabits to just one megabit. In addition, the image was divided into 30 independent areas. This reduced the likelihood of losing an entire image at once in transit to Earth.
This section gives a short summary of the mission sequence of the two rovers. A more detailed description can be found in the articles by Spirit and Opportunity .
Spirit landed in Gusev Crater (14.57 degrees south and 175.47 degrees west) on January 4th at 4:35 UTC (Earth time). After the problem-free landing, Spirit sent the first recordings of the area, which is relatively poor in larger stones. Within 12 sols, the rover unfolded and was prepared to descend from the lander. During this time the instruments were also tested. After the rover had rotated 120 ° on the platform, it drove off the platform on January 15th. First a stone called "Adirondack" should be examined. During this investigation, contact with Spirit was almost completely lost, and rudimentary contact could only be re-established a few days later. The reason was that the rover's computer was permanently restarted due to a software error. After reformatting the computer's flash memory, the rover on Sol 33 (February 6, 2004) was able to resume work on Adirondack. It turned out that the stones in Spirit's surroundings were mainly volcanic in nature and showed no clear signs of water exposure. To get to the original bedrock, Spirit drove towards the larger Bonneville crater during the primary mission . Here it turned out that this was almost completely filled with sand and did not show any of the hoped-for rock outcrops.
So it was decided to bring Spirit to the Columbia Hills nearly 2.5 kilometers away. The rover reached the base of these mountains in June 2004. In more than a year and a distance of 4.81 kilometers, Spirit then climbed the highest mountain called "Husband Hill" on August 21, 2005. While examining the stones on the slopes The first clear indications of the influence of water were discovered on the mountain. During the ascent, the power supply suddenly improved because the dust devil had almost completely freed the solar panels from the deposited dust. By February 2006, Spirit was shutting down and reaching the "Home Plate" formation, which showed stratified stone deposits and is likely to be volcanic in nature.
After investigations at home plate, Spirit was supposed to investigate McCool Hill, but was stopped by a wheel now completely blocked. Therefore, Spirit wintered on a low rocky ridge called "Low Ridge Haven". After the winter, Spirit continued investigating home plate. The stuck front wheel churned up light sand. This consisted of 90% silicates, the formation of which could only be explained by the existence of water. From June 2007 to the end of August 2007, a dust storm meant that Spirit could not do any examinations due to the greatly reduced solar radiation. At the beginning of 2008 Spirit was positioned on the north side on a steeper descent of home plate in order to receive the upcoming winter with the maximum possible energy. From the middle of August 2008 Spirit began again with limited examinations, as the power supply from the again very dusty solar cells was still very low.
Spirit as a stationary probe at Troy
In December 2008, Spirit began an extended voyage to two geological formations, informally known as "Goddard" and "von Braun". Since the shorter route could not be reached via home plate, it was decided to bypass home plate on the north side and then drive to the two destinations on its west side. While driving in the direction of “von Braun”, Spirit's wheels dug into the loose sand on April 26, 2009 so far that it was initially no longer possible to advance. NASA used a test rover to investigate the possibilities of releasing the rover. Several unsuccessful attempts were made to free the rover by carefully driving back and forth. At the beginning of 2010, NASA decided to leave the rover in this location and only examine the surrounding area using a robot arm. Preparations for the winter have started (alignment of the solar cells) to ensure the energy supply. With the upcoming Martian winter, Spirit could no longer generate enough energy and switched itself into a hibernation mode. The last radio signals from the rover were received on March 22, 2010 - Spirit has been silent since then. NASA tried unsuccessfully to communicate with the rover in the months that followed. On May 25, 2011, the rover was abandoned by NASA, as it was assumed that the long winter time without enough energy for heating must have led to irreparable defects in the electronics.
Opportunity landed at Meridiani Planum (1.95 degrees south and 354.47 degrees west) on January 25, 2004 at 5:05 UTC. On this plain, poor in craters, the lander came to rest in the middle of a small crater called "Eagle Crater". After only 6 days, Opportunity was able to shut down the lander. Only a few meters further on, the rover was able to examine a small stratified rock outcrop at the crater rim. Here, structures were discovered that can only arise in running water and that have a high hematite content. It turned out that larger areas in the crater and in the entire plain are covered by small spherules (called spherules or blueberries ) made of hematite. After examining the Eagle crater, the Endurance crater at a distance of 800 m was selected as a new target , which with a depth of 20 m revealed even more of the history of the Meridiani plain. Opportunity reached the crater at the end of the primary mission. The rover first circumnavigated the crater partially to find an entry route into the crater. Layered structures have also been discovered on the crater walls. The descent into the crater began in June 2004. The stone layers were examined at regular intervals with the stone grinding tool, the microscope and the spectrometer. After examining a steep crater wall, the rover exited the crater in December 2004.
On the way to the Victoria Crater
The next target, which promised more information about the history of the plain, was the even larger Victoria Crater, 6000 m away to the south. Several smaller craters were examined along the way. The rover passed its own heat shield, and the unique opportunity arose to examine this component after its use. In the process, Opportunity also came across an iron meteorite, which was also examined. During the trip in the Meridiani plain, the rover made very good progress and sometimes drove 200 m per day. On April 26, 2005, the rover got stuck in a small sand dune, from which it was only able to free itself five weeks later. On the way further small craters were passed and explored, some of which were heavily buried under the desert sand.
At the end of September 2006 the rover had reached the crater Victoria and was able to take the first photographs of the crater interior. Here, too, layered stone structures were discovered at the crater edges. Now Opportunity first circumnavigated the crater a quarter to the north to take more photographs and again to find an entry point. He was supported from orbit by high-resolution images from the Mars Reconnaissance Orbiter . The crater itself has a diameter of 750 m and is therefore five times larger than the endurance crater that has already been investigated . In June 2007, the rover was supposed to enter the Victoria Crater at the point where it originally arrived. However, he was initially prevented from doing so by the same dust storm as Spirit and one had to take care of maintaining the energy supply. After the storm subsided and the atmosphere cleared again, the rover drove into the crater and almost reached one of the layered cliffs. At the end of August 2008, Opportunity drove out of the crater again because it was feared that the front wheel might lock.
Cape York at the Endeavor Crater
The next target for Opportunity was the 22 km Endeavor Crater , approximately 12 km in the direct distance. The journey time was estimated to be at least two years. It was hoped to be able to investigate even deeper rock layers there. Since the attempt was made to drive over unproblematic terrain as far as possible, the route was extended to 19 km. On December 16 (Sol 2450) the rover reached the 80 m large crater “Santa Maria” and examined it more closely until March. The rover was able to cover the remaining 6 km until August 10, 2011, and after a problem-free journey it reached its first destination at the edge of the Endeavor crater, Cape York. The total distance covered was 21 km, which was covered in almost 3 years of driving time. At Cape York a stone was examined that was probably modified by hot water. In addition, gypsum veins were discovered for the first time on Mars, which must also have been caused by water. In the course of 2014, the rover climbed one of the outskirts of the crater, "Cape Tribulation", in the south of Cape York. In 2015 the rover drove to the so-called Marathon Valley to continue looking for clayey rocks. Then the rover drove on to the Perseverance Valley, where a gully was discovered in orbital images, which could have been created by running water. This structure was examined in 2017 and 2018. In June 2018, a dust storm broke out that quickly enveloped the entire planet. As a result, the solar panels could no longer generate electricity for the probe, which is why communication broke off. The Opportunity spacecraft has not received a signal since June 10, the 5111st day of Mars (Sol) since landing. On February 13, 2019, NASA stopped its attempts to contact again and officially declared the Mission Opportunity over.
Operation at NASA
During the flight phase, the science team trained the mission sequence with two identical test models of the rovers. The same computer programs were used as later in the real operation, and the time lag in communication with Mars was also taken into account. These test runs sometimes lasted weeks and served to ensure that the team got to know the controls of the complex machines and worked well together in the hot phase of the primary mission.
During the primary mission, the working hours for those involved in the mission were adjusted to Mars time so that there are no idle times during the operation of the rovers. Since a Martian day lasts about 40 minutes longer than an Earth day, the working hours are shifted every day. NASA also made special clocks available for this purpose, which were aligned with the Martian time and were intended to help the employees coordinate the meetings. The mission team with engineers and scientists was divided into two teams, each looking after a rover. For this purpose, two floors were set up in a building in the JPL complex, which differ in color (red color markings for Spirit, blue for Opportunity) so that employees can better orient themselves.
Since the rovers had landed in exactly opposite places on Mars, one shift on one team began its work when the other team had just finished its shift. At the beginning of the shift, in the old NASA tradition, a wake-up song was played to “wake up” the rover. The selected songs mostly had a relation to the current task of the day. When the mission was extended, shift work was reorganized into normal working hours. The rovers no longer received their orders every day, but only every other day, or a longer action plan over the weekend.
Operation of the rover
Since direct control of the rover was not possible due to the signal run time of an average of 20 minutes, each operation had to be planned in advance. This happened on earth through the use of simulation and planning software. In addition, there were two identical rovers on earth, with which the desired actions could be safely tested before they were carried out on Mars. This was necessary, for example, to maneuver the stuck Rover Opportunity out of a sand dune.
Planning a rover operation
First, the engineers and scientists evaluated the results of the previous job on the rover. It was checked whether the rover could carry out all actions or whether and for what reasons it had to abort. Based on the recorded images, 3D models were designed that depicted the surroundings as much as possible. The "Science Activity Planner (SAP)" software helped. This software automatically created panoramas of the surroundings, offered a three-dimensional representation of the rover in its surroundings and an evaluation of the recorded spectra. The speed at which the data was prepared and made available was also important, as a new plan had to be available within the next few hours. The high-resolution images from the cameras of the Mars orbiters, which can also be used to create a rough 3D model of the landscape, were also helpful. These results were evaluated by a scientific group ( Science Operating Working Group ), which then defined new goals. When planning the activities and observations for the next sol, the condition of the rover had to be taken into account, e.g. B. Charge status of the battery, power requirement of each action, position of the sun, consideration of the transmission times of the data via the orbiters.
The route the rover had to drive to the next destination also had to be planned. There were several ways to navigate the rover. In the case of the controlled drive, the route was specified and the motors were also precisely controlled. With the “Visual Odometry” method, the distance determined was compared with the image recordings based on the measured wheel revolutions in order to determine the actual locomotion. This was especially helpful on sandy bottoms when the rover was sliding on the ground. On the basis of the recorded images, the rover automatically recognized the route. Using the “local path selection” method, he also recognized obstacles on the route, determined an alternative route and avoided the object independently. Only special prohibited zones were defined into which the rover was not allowed to steer. The long journeys of over 100 m during the mission could only be solved with this intelligent software, as the planning on earth based on stereo images did not go as far. The intelligent control could z. B. Spirit can cope with the route to the Columbia Hills 50% faster than with just a controlled drive. The rover received support from the sun. He was able to determine his current orientation and position based on the position of the sun. This was done by taking a picture of the sun at the expected location and then analyzing the image to find out the true position of the sun.
A few days a year, Mars disappears behind the sun when viewed from Earth ( conjunction ). During this time, communication with the Mars probes is not possible due to the influence of the sun. The rovers stood still during this time, but took panoramic photos and examined the atmosphere or stones with the Mössbauer spectrometer.
The total cost of the primary mission was $ 820 million, of which $ 645 million was spent on developing spacecraft and scientific instruments. The rocket launch cost $ 100 million, $ 75 million went to the mission operation and scientific evaluation. The additional operating costs for both rovers were $ 20 million per year.
Cooperation with other Mars missions
During the landing phase, data from the Mars Rover Lander was also sent via the UHF antenna to the Mars Global Surveyor Orbiter in order to monitor the landing. Shortly after landing, Spirit's landing site was photographed by the MGS Orbiter on January 19, 2004 in a resolution that also identified the parachute, the heat shield and the airbag prints. The same was achieved from the Opportunity landing area on February 9, 2004.
This information was used by the rover planners to determine the exact landing location, to plan the routes to be traveled and to identify recorded objects on the Mars horizon. Both landing areas were subsequently photographed several times from different angles in order to obtain a 3D model of the topography. This was important, for example, to find slopes during the Martian winter where the rover can best spend the winter on an incline, or to find a route into a crater.
After the arrival of the Mars Reconnaissance Orbiter with its high-resolution HiRISE color camera, detailed images of the current surroundings of the Mars rovers could be made, in which even the lanes could be seen. Joint measurements of the atmosphere and the environment were also made from the ground and from orbit. The Rover Opportunity and the Orbiter Mars Global Surveyor have similar instruments: the MiniTES on Opportunity and a normal Thermal Emission Spectrometer (TES) in the orbiter. Opportunity analyzed the atmosphere with an upward view, while the Global Surveyor recorded it with a downward view. This enabled a detailed profile of the atmosphere to be obtained and the dust composition to be analyzed more precisely.
During the global dust storm in 2007, its spread could be closely followed by the orbiters in order to provide information on the expected deterioration in solar radiation for the rovers on the ground. Most communication takes place via the Mars Odyssey Orbiter; however, it can also be communicated via the Mars Reconnaissance Orbiter and via the European orbiter Mars Express .
The names of the two rovers were determined through a school competition. The winning entry was Sofi Collis, a nine-year-old Russian-American student from Arizona.
I used to live in an orphanage. It was dark and cold and lonely. At night, I looked up at the sparkly sky and felt better. I dreamed I could fly there. In America, I can make all my dreams come true. Thank you for the 'Spirit' and the 'Opportunity'.
“I once lived in an orphanage. It was dark and cold and lonely. During the night I looked up at the sparkling sky and felt better. I dreamed I could fly there. In America I can make all my dreams come true. Thank you for the spirit of optimism and the opportunity. "
During the development of the rovers, these were known as MER-1 (Opportunity) and MER-2 (Spirit). NASA internally refers to them as MER-A (Spirit) and MER-B (Opportunity), in the order they landed on Mars.
The mission was accompanied by a film team during the planning phase right through to the primary mission. This resulted in the IMAX film “ Roving Mars ”.
Shortly after transmission over the Internet, the images were available free and unprocessed. In the month after Spirit landed, NASA's website had 6.34 billion hits and 914 million web pages were downloaded. A total of 48,000 people watched the NASA Internet broadcast of Spirits Landing. For this purpose, an Internet fan community was formed, which regularly processed them and generated color images or panorama photos from them. The mission was also accompanied by its own blogs and websites. The planning software SAP was also freely available in its own version called Maestro.
Science magazine recognized the discovery that salty, acidic water once existed on the surface of Mars as “Breakthrough Of The Year 2004”. The entire mission team received the 2007 Sir Arthur Clarke Award.
In 2008 (German version: 2009) the N24 documentary Five Years on Mars was created , which reports on the activities of the two rovers during their first four years.
A more detailed description of the results can be found on the Scientific Results of the Mars Exploration Rover Mission page .
The rovers have provided important clues to confirm the primary scientific goals: Finding and characterizing different stones and soils that show evidence of former influence of water. In particular, Opportunity's research at Meridiani-Planum produced much evidence that water played a role in the history of Mars. In the vicinity of Opportunity's landing area, so-called spherules were discovered for the first time , which cover entire surfaces as small spheres and consist of hematite , which usually forms in water. Stones that were changed by the influence of water could also be found with Spirit. For example, in the Clovis rock formation, the Mössbauer spectrometer found the mineral goethite , which only forms in water. In the home plate area, Spirit had digged up the ground and found white sand that was 90% silicate . Such deposits form from soils in connection with hot steam from volcanic activity or it forms from water from hot springs.
The investigation of the stone Bounce Rock from Opportunity showed that its composition differs greatly from the rocks investigated so far, but is very similar to the shergottites, a subgroup of the Martian meteorites . This is another strong indication that the Martian meteorites really came from Mars.
Spirit was able to photograph dust devils in action, which are common in Gusev Crater. The sky is regularly photographed in order to observe the formation of high veil clouds and to determine the transparency of the atmosphere. During the global dust storm, the two rovers, in combination with the Mars orbiters, were able to observe the rise and fall of the dust content of the atmosphere. Furthermore, a detailed temperature profile of the Martian atmosphere was created by simultaneous measurements by Opportunity in combination with the Mars Global Surveyor.
The rovers made astronomical observations. For example, the passage of the Martian moons in front of the sun was observed in order to obtain better orbit determinations for them and the constellation Orion was recorded to test the camera for future night observations. Other planets have also been observed, such as Jupiter (Sol 681-694, Opportunity) or Earth .
- Mars Exploration Rover website of NASA (English)
- Product collection of the Planetary Society (English)
- Collection of articles from Astronews.com
- Mars Exploration Rover
- Compilation of the most important scientific results (NASA )
- scinexx.de: A Thousand Days of Mars - The Mars Exploration Rover Mission August 26, 2005
- ↑ Jim Bell: Postcards from Mars: The First Photographer on the Red Planet . Ed .: Spectrum Academic Publishing House. 1st edition. 2007, ISBN 978-3-8274-1969-9 , pp. 10-18 .
- ^ A b Steven W. Squyres: Roving Mars . Ed .: Hyperion. 1st edition. 2005, ISBN 1-4013-0149-5 .
- ^ The scientific objectives of the Mars Exploration Rover. NASA, July 12, 2007, accessed September 19, 2008 .
- ↑ Golombek, MP, et al .: Selection of the Mars Exploration Rover landing sites . In: J. Geophys. Res. Vol. 108, E12, December 10, 2003 ( mars.asu.edu [PDF; accessed September 19, 2008]).
- ↑ a b c d e NASA (ed.): Mars Exploration Rover Launches . Press kit. June 2003 ( marsrover.nasa.gov [PDF; accessed September 23, 2008]).
- ^ Spacecraft: Cruise Configuration. NASA / JPL, October 5, 2005, accessed September 19, 2008 .
- ↑ Spacecraft: Aero Shell. NASA / JPL, October 5, 2005, accessed September 19, 2008 .
- ^ Allen Witkowski, Robin Bruno: Mars Exploration Rover Parachute Decelerator System Program Overview. (PDF; 2.9 MB) (No longer available online.) American Institute of Aeronautics and Astronautics, archived from the original on May 1, 2009 ; Retrieved September 19, 2008 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Mission Fantastic to Mars (Part 3). NASA / JPL, August 26, 2006, accessed September 19, 2008 .
- ^ Spacecraft: Airbags. NASA / JPL, July 12, 2007, accessed September 23, 2008 .
- ^ In-situ Exploration and Sample Return: Entry, Descent, and Landing. NASA / JPL, July 12, 2007, accessed September 23, 2008 .
- ↑ Spacecraft: Lander. NASA / JPL, July 12, 2007, accessed September 23, 2008 .
- ^ Spirit Lands On Mars and Sends Postcards. NASA / JPL, January 4, 2004, accessed September 23, 2008 .
- ↑ NASA Hears From Opportunity Rover On Mars. NASA / JPL, January 25, 2004, accessed September 23, 2008 .
- ↑ Step-by-Step Guide to Entry, Descent, and Landing. NASA / JPL, July 12, 2007, accessed September 30, 2008 .
- ↑ a b c d e Mars Exploration Rover Landings . January 2004 ( nasa.gov [PDF; accessed September 30, 2008]).
- ↑ Once again, NASA relies on maxon technology. 2017, accessed February 14, 2019 .
- ^ Spacecraft: Surface Operations: Rover. NASA, 2004, accessed September 23, 2008 .
- ^ Technologies of Broad Benefit: Avionics. NASA, 2004, accessed September 23, 2008 .
- ↑ sol 408-414, March 31, 2005: Opportunity Continues to Set Martian Records. NASA, 2004, accessed September 23, 2008 .
- ↑ International Interplanetary Networking Succeeds. NASA, February 13, 2004, accessed September 30, 2008 .
- ^ Opportunity All 2007, sol 1343-1348. NASA, November 13, 2007, accessed September 30, 2008 .
- ↑ Communications With Earth. NASA, July 12, 2007, accessed September 30, 2008 .
- ^ Spacecraft: Surface Operations: Rover. NASA, 2003, accessed September 27, 2008 .
- ^ Technologies of Broad Benefit: Avionics. NASA / JPL, accessed September 23, 2008 .
- ^ A Conversation with Mike Deliman. acm.org, 2004, accessed September 23, 2008 .
- ^ Technologies of Broad Benefit: Software Engineering. NASA / JPL, accessed September 23, 2008 .
- ↑ Spacecraft: Nasa leaves Mars robots stuck in the sand. NZZ, January 27, 2010, accessed on January 18, 2010 .
- ↑ "NASA Mars Rover Arrives at New Site on Martian Surface" from August 10, 2011 on nasa.gov , accessed on August 8, 2012.
- ↑ "At Mars Crater, NASA Rover Finds Evidence of Ancient Water Hotspot" from September 1, 2011 on space.com , accessed on August 8, 2012.
- ↑ Nasa gives up Mars rover "Opportunity". Spiegel Online , February 13, 2019, accessed on the same day.
- ↑ Mission to Mars, WORKING CRUISE. NASA / JPL, September 2003, accessed September 30, 2008 .
- ^ Mars Exploration Rover Operations with the Science Activity Planner. (PDF; 1.8 MB) (No longer available online.) NASA / JPL, archived from the original on May 27, 2010 ; Retrieved April 16, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Week In Review July 3 - July 9. NASA / JPL, accessed September 24, 2008 .
- ↑ Mark W. Maimone and P. Chris Leger and Jeffrey J. Biesiadecki: Overview of the Mars Exploration Rovers' Autonomous Mobility and Vision Capabilities . In: IEEE International Conference on Robotics and Automation (ICRA) Space Robotics Workshop . April 14, 2007 ( www-robotics.jpl.nasa.gov [PDF; accessed September 27, 2008]).
- ↑ Budget Cuts Could Shut Down Mars Rover. space.com, 2006, accessed March 24, 2008 .
- ^ MGS MOC Images of Mars Exploration Rover, Opportunity, on Mars. NASA, February 9, 2004, accessed September 28, 2008 .
- ↑ constraints on dust aerosols from the Mars Exploration Rover using MGS over flights and Mini-TES. NASA, July 2, 2006, accessed September 28, 2008 .
- ↑ International Interplanetary Networking Succeeds. NASA, February 13, 2004, accessed September 28, 2008 .
- ↑ NASA Portal Makes A Little Bit Of Mars Available To Everyone On Earth. NASA, February 19, 2004, accessed September 28, 2008 .
- ^ New Mars Data for Maestro: Opportunity # 1. SpaceRef, February 13, 2004, accessed April 23, 2013 .
- ↑ Science's Breakthrough Of The Year: Salty, Acidic Soup Could Have Supported Life On Mars. Science, 2004, accessed September 25, 2008 .
- ^ The Sir Arthur Clarke Awards - Recognizing UK achievements in Space. (No longer available online.) 2007, archived from the original on May 9, 2008 ; Retrieved September 25, 2008 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ^ Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet. ESA, March 2, 2004, accessed September 30, 2008 .
- ↑ Silica-Rich Soil Found by Spirit. ESA, May 21, 2007, accessed September 30, 2008 .
- ↑ Week in Review April 10 - April 16. ESA, April 2004, accessed September 30, 2008 .
- ↑ "Martian meteorites" actually come from Mars. ESA, April 15, 2004, accessed September 30, 2008 .
- ^ JF Bell II, among others: Solar Eclipses of Phobos and Deimos Observed from the Surface of Mars. In: Nature. Vol. 436, July 2005, pp. 55-57.
- ↑ Press Release Images: Spirit. NASA / JPL, March 11, 2004, accessed September 30, 2008 .