Mars 2020 rover mission of NASA/JPL
Mars 2020 Mission Overview. The Mars 2020 rover mission is part of NASA's Mars Exploration Program, a long-term effort of robotic exploration of the Red Planet. The Mars 2020 mission addresses high-priority science goals for Mars exploration, including key questions about the potential for life on Mars. The mission takes the next step by not only seeking signs of habitable conditions on Mars in the ancient past, but also searching for signs of past microbial life itself. The Mars 2020 rover introduces a drill that can collect core samples of the most promising rocks and soils and set them aside in a "cache" on the surface of Mars. The mission also provides opportunities to gather knowledge and demonstrate technologies that address the challenges of future human expeditions to Mars. These include testing a method for producing oxygen from the Martian atmosphere, identifying other resources (such as subsurface water), improving landing techniques, and characterizing weather, dust, and other potential environmental conditions that could affect future astronauts living and working on Mars. 1) 2) 3)
The mission is timed for a launch opportunity in July/August 2020 when Earth and Mars are in good positions relative to each other for landing on Mars. That is, it takes less power to travel to Mars at this time, compared to other times when Earth and Mars are in different positions in their orbits. To keep mission costs and risks as low as possible, the Mars 2020 design is based on NASA's successful Mars Science Laboratory mission architecture, including its Curiosity rover and proven landing system.
Mars 2020 Science
The Mars 2020 rover explores a site likely to have been habitable. It will seek signs of past life, set aside a returnable cache with the most compelling rock core and soil samples, and demonstrate technology needed for the future human and robotic exploration of Mars. 4)
Figure 1: Evolving science strategies for Mars Explorations (image credit: NASA)
Leveraging discoveries from past Mars missions about water and habitability on Mars, the Mars 2020 rover represents a shift toward directly seeking signs of past microbial life.
NASA's Mars Exploration Program has a long-term, systematic exploration plan for the Red Planet. Mars missions build on each other, with discoveries and innovations made by prior missions guiding what comes next. Mars missions are guided by evolving, discovery-driven science strategies that provide continuity in Mars science exploration themes.
The first framing theme guiding Mars exploration was "Follow the Water," as water is essential to habitable environments and life as we know it. It is also important to understanding the geologic and climatic history of Mars, and would likely play a role in supporting future human explorers.
With past orbiters, landers, and rovers finding evidence of water, the theme "Explore Habitability" emerged to look for additional conditions necessary to life, including chemical elements and compounds necessary for life as we know it. Findings from the Mars Science Laboratory's Curiosity rover marked a transition to the current science theme: "Seek Signs of Life."
While Curiosity is seeking evidence of habitable conditions (both past water and the chemistry needed for life), Mars 2020 is seeking signs of past life itself in the geologic record.
The Mars 2020 Mission Contributes to Four Science Goals for Mars Exploration
Studying Mars' Habitability, Seeking Signs of Past Microbial Life, Collecting and Caching Samples, and Preparing for Future Human Missions. The science strategy for NASA's Mars Exploration Program (MEP) is to Seek Signs of Life. The Mars 2020 rover contributes to this strategy, as well as to the Program's four long-term science goals: 5)
• Goal 1: Determine whether life ever existed on Mars. The mission of the Mars 2020 rover focuses on surface-based studies of the Martian environment, seeking preserved signs of biosignatures in rock samples that formed in ancient Martian environments with conditions that might have been favorable to microbial life.
- It is the first rover mission designed to seek signs of past microbial life. Earlier rovers first focused on and confirmed that Mars once had habitable conditions.
• Goal 2: Characterize the Climate of Mars. Past Martian climate conditions are a focus of the Mars 2020 rover mission. The rover's instruments are looking for evidence of ancient habitable environments where microbial life could have existed in the past.
• Goal 3: Characterize the Geology of Mars. The Mars 2020 rover is designed to study the rock record to reveal more about the geologic processes that created and modified the Martian crust and surface through time. Each layer of rock on the Martian surface contains a record of the environment in which it was formed. The rover seeks evidence of rocks that formed in water and that preserve evidence of organics, the chemical building blocks of life.
• Goal 4: Prepare for Human Exploration. The Mars 2020 rover is demonstrating key technologies for using natural resources in the Martian environment for life support and fuel. It is also monitoring environmental conditions so mission planners understand better how to protect future human explorers.
- This science goal relates to national space policy for sending humans to Mars in the 2030s. Similar to the history of the exploration of Earth's moon, robotic missions to Mars provide a crucial understanding of the environment and test innovative technologies for future human exploration.
- Investments in Mars 2020 technologies include contributions from NASA's Human Exploration and Operations (HEO) Mission Directorate and Space Technology Program (STP) as part of NASA's long-term efforts to develop future capabilities for human space exploration.
The spacecraft is the protective "spaceship" that enables the precious cargo (that is, the rover!) to travel between Earth and Mars. It is separate from the launch vehicle that carries the spacecraft and the rover outside of Earth's atmosphere and gravitational pull. The spacecraft includes the mechanical units that safely carry and maneuver the rover through the Martian atmosphere to a landing on Mars.
The three major parts of the Mars 2020 mission spacecraft design are based on the successful Mars Science Laboratory mission:
• Cruise Stage: The configuration for travel between Earth and Mars that includes an aeroshell (backshell with heat shield) in which the rover and its landing system are enclosed.
• Entry, Descent, and Landing System: The configuration for entry into the Martian atmosphere. Includes the aeroshell, parachute, descent vehicle, and structure for a sky-crane maneuver that will lower the rover to the Martian surface on tethers.
• Rover: A wheeled vehicle with science instruments for making discoveries on the Martian surface.
Figure 2: Illustration of the Mars 2020 spacecraft (image credit: NASA)
Technology development makes missions possible.
Each Mars mission is part of a continuing chain of innovation. Each relies on past missions for proven technologies and contributes its own innovations to future missions. This chain allows NASA to push the boundaries of what is currently possible, while still relying on proven technologies.
The Mars 2020 mission leverages the successful architecture of NASA's Mars Science Laboratory mission by duplicating most of its entry, descent, and landing system and much of its rover design.
The mission advances several technologies, including those related to priorities in the National Research Council's 2011 Decadal Survey and for future human missions to Mars. Plans include infusing new capabilities through investments by NASA's Space Technology Program, Human Exploration and Operations Mission Directorate, and contributions from international partners.
Many innovations focus on entry, descent, and landing technologies, which help ensure precise and safe landings. They include sensors to measure the atmosphere, cameras and a microphone, and at least two key ways to reach the surface of Mars with greater accuracy and less risk (Range Trigger and Terrain-Relative Navigation).
Figure 3: The cruise stage, aeroshell, descent stage, rover and heat shield together make up the spacecraft. As the spacecraft travels down through the Martian atmosphere, certain parts fall away one by one until the rover is safely on solid Martian ground (image credit: NASA)
Figure 4: Leveraging heritage technology: Mars Rover Curiosity's sky-crane maneuver. This artist's concept shows the sky-crane maneuver during the descent of NASA's Curiosity rover to the Martian surface. The Mars mission launching in 2020 would leverage the design of this landing system and other aspects of the Mars Science Laboratory architecture (image credit: NASA/JPL-Caltech)
Mars 2020 Rover
The Mars 2020 rover is car-sized, about about 3 m long, 2.7 m wide, and 2.2 m tall (not including the arm). But at 1,050 kg, it weighs less than a compact car. In some sense, the rover parts are similar to what any living creature would need to keep it "alive" and able to explore. 6)
Figure 5: The Mars 2010 rover is a wheeled vehicle with science instruments for making discoveries on the Martian surface (image credit: NASA)
Figure 6: Mars 2020 Rover build update. Tour the Spacecraft Assembly Facility at NASA's Jet Propulsion Laboratory and see the Mars 2020 mission under construction. Project System Engineer Jennifer Trosper explains the hardware being built and tested, including the rover, descent stage, cruise stage, back shell, and heat shield (video credit: NASA/JPL-Caltech, Published on 19 February 2019)
The Mars 2020 Rover has the following parts: 7)
• body: a structure that protects the rover's "vital organs"
• brains: computers to process information
• temperature controls: internal heaters, a layer of insulation, and more
• "neck and head": a mast for the cameras to give the rover a human-scale view
• eyes and ears : cameras and instruments that give the rover information about its environment
• arm and "hand": a way to extend its reach and collect rock samples for study
• wheels and legs: parts for mobility
• electrical power: batteries and power
• communications: antennas for "speaking" and "listening"
The Mars 2020 rover body is based on the Mars Science Laboratory's Curiosity rover configuration. However, the Mars 2020 rover has a new science and technology toolbox. An important difference is that this rover can sample and cache minerals. To do so, the rover has a new coring drill to collect samples. The samples are then sealed in tubes and placed on the surface of Mars. - In the future, another space mission could potentially pick up the samples and bring them to Earth for detailed analysis. 8)
Differences between Mars 2020 and Curiosity
The large robotic arm on the front of the rover differs from Curiosity's for two main reasons:
1) Mars 2020 will collect rock cores. Mars 2020 needs to collect rock core samples and save them for possible future study by scientists. Curiosity studied samples collected onsite, using the rover's onboard laboratory.
2) Mars 2020 has a larger "hand," or turret. Mars 2020's new functions and new science tools means it must accommodate a larger turret at the end of the robot arm. This turret has the coring drill and two science instruments, plus a color camera for close-up surface inspection and also "selfies" for engineering health checkups.
There is an internal workspace inside the rover body that is dedicated to picking up, moving and placing drill bits and sample tubes within the Sample Caching System. New motors that drive these specialized movements were needed beyond those used on rover Curiosity. The rover motor controller electronics have been modified from the Curiosity design to accommodate these motors.
New Software to Operate the Rover
Mars 2020 will operate very differently than Curiosity. The new rover will gather 20 sealed samples of Martian rocks and soil. The samples will be set aside in a "cache" on Mars. The team is building new software to run the rover. The software will be updated with improvements throughout the mission.
Besides just managing the new sampling operations, the Mars 2020 rover manages all of its daily activities more efficiently to balance its on-site science measurements while also collecting samples for potential future analysis. To do that, the rover's driving software - the "brains" for moving around — was changed to give Mars 2020 greater independence than Curiosity ever had.
This allows Mars 2020 to cover more ground without consulting controllers on Earth so frequently. Also, engineers have added a "simple planner" to the flight software. This allows more effective and autonomous use of electrical power and other rover resources. It allows the rover to shift the time of some activities to take advantage of openings in the daily operations schedule.
New Wheels for Mars 2020
Engineers redesigned the Mars 2020 wheels to be more robust due to the wear and tear the Curiosity rover wheels endured while driving over sharp, pointy rocks. Mars 2020's wheels are narrower than Curiosity's, but bigger in diameter and made of thicker aluminum.
The combination of the larger instrument suite, new Sampling and Caching System, and modified wheels makes Mars 2020 heavier than its predecessor, Curiosity.
The Mars 2020 Rover's "Brains"
The computer module is called the Rover Compute Element (RCE) - there are actually two identical RCEs in the body so there is always a spare "brain." 9)
The RCE interfaces with the engineering functions of the rover over two networks which follow an aerospace industry standard designed especially for the high-reliability requirements of airplanes and spacecraft. In addition, the RCEs have a special purpose to direct interfaces with all of the rover instruments for exchange of commands and science data.
- Processor: Radiation-hardened central processor with PowerPC 750 Architecture: a BAE RAD 750. It operates at up to 200 MHz speed, 10 times the speed in Mars rovers Spirit and Opportunity's computers.
- Memory: 2 GB of flash memory (~8 times as much as Spirit or Opportunity). 256 MB of dynamic random access memory. 256 kB of electrically erasable programmable read-only memory.
The Cameras on the Mars 2020 Rover
The rover has several cameras focused on engineering and science tasks. Some help us land on Mars, while others serve as our “eyes” on the surface to drive around. We use others to do scientific observations and aid in the collection of samples. 10)
- Main function: Take pictures, looking up and down, during descent through Martian atmosphere.
- Location: Mounted on the fore-port-side of the rover, pointing toward the ground.
- Main function: Used for driving around on Mars and for positioning the tools on the robotic arm
- Location: Various places on the rover
- Mass: < 425 grams
- Image size: 5120 x 3840 pixels
- Image resolution: 20 Mpixel
• Science Cameras The science cameras are:
- MastCam-Z is a pair of cameras that takes color images and video, three-dimensional stereo images, and has a powerful zoom lens. Like the Mastcam cameras on the Curiosity rover, Mastcam-Z on Mars 2020 consists of two duplicate camera systems mounted on the mast that stands up from the rover deck. The cameras are next to each other and point in the same direction, providing a 3D view similar to what human eyes would see, only better. They also have a zoom function to see details of faraway targets.
- SuperCam, fires a laser at mineral targets that are beyond the reach of the rover’s robotic arm, and then analyzes the vaporized rock to reveal its elemental composition. Like the ChemCam on rover Curiosity, SuperCam fires laser pulses at pinpoint areas smaller than 1 mm from more than 7 meters away. Its camera and spectrometers then examine the rock's chemistry. It seeks organic compounds that could be related to past life on Mars. When the laser hits the rock, it creates plasma, which is an extremely hot gas made of free-floating ions and electrons. An on-board spectrograph records the spectrum of the plasma, which reveals the composition of the material.
- PIXL, uses X-ray fluorescence to identify chemical elements in target spots as small as a grain of table salt. It has a Micro-Context Camera to provide images of to correlate its elemental composition maps with visible characteristics of the target area.
- SHERLOC. Its main tools are spectrometers and a laser, but it also uses a macro camera to take extreme close-ups of the areas that are studied. This provides context so that scientists can see textures that might help tell the story of the environment in which the rock formed.
- WATSON. This camera is one of the tools on the "arm" or turret at the end of Curiosity's robotic arm. It is almost identical to the MAHLI hand-lens camera on the Curiosity rover. WATSON captures the larger context images for the very detailed information that SHERLOC collects on Martian mineral targets. WATSON provides views of the fine-scale textures and structures in Martian rocks and the surface layer of rocky debris and dust. Since WATSON can be moved around on the robotic arm, it also provides other images of rover parts and geological targets that can be used by other arm-mounted instruments. For example, it can be pointed at the oxygen-making experiment MOXIE to help monitor how much dust accumulates around the inlet that lets in Martian air for the extraction of oxygen. - A calibration target for WATSON is attached to the front of the rover body. It contains, a metric standardized bar graphic to help calibrate the instrument.
Figure 7: Overview of the Cameras on the Mars 2020 Rover (image credit: NASA)
Mars 2020 communications
Mars 2020 has three antennas that serve as both its "voice" and its "ears." They are located on the rover equipment deck (its "back"). Having multiple antennas provides operational flexibility and back-up options just in case they are needed. Antennas on rover deck: 11)
UHF antenna: Most often, Mars 2020 uses its ultra-high frequency (UHF) antenna (about 400 megahertz) to communicate with Earth through NASA's orbiters around Mars. Because the rover and orbiter antennas are within close range of each other, they act a little like walky-talkies compared to the long-range telecommunications with Earth provided by the low-gain and high-gain antennas.
It generally takes about 5 to 20 minutes for a radio signal to travel the distance between Mars and Earth, depending on planet positions. Using orbiters to relay messages is beneficial because they are much closer to the rover than the Deep Space Network (DSN) antennas on Earth. The mass- and power-constrained rover can achieve high data rates of up to 2 Mbit/s on the relatively short-distance relay link to the orbiters overhead. The orbiters then use their much larger antennas and transmitters to relay that data on the long-distance link back to Earth.
- Main function: Transmitting data to Earth through Mars Orbiters
- Radio frequency: UHF-band at ~400 MHz
- Transmission rates: Up to 2 Mbit/s on the rover-to-orbiter relay link.
X-band High-Gain Antenna: The high-gain antenna is steerable so it can point its radio beam in a specific direction. The benefit of having a steerable antenna is that the entire rover doesn't need to change position to talk to Earth, which is always moving in the Martian sky. Like turning your neck to talk to someone beside you rather than turning your entire body, the rover can save energy and keep things simple by moving only the antenna. Its high gain allows it to focus its beam, allowing higher data rates on the long link back to Earth.
- Main function: Transmitting data directly to and from Earth
- Radio frequency: X-band (7 to 8 GHz)
- Size: Hexagonally shaped, 0.3 m in diameter
- Transmission/ Reception Rates: 160/500 bit/s or faster to/from the Deep Space Network's 34 m diameter antennas or at 800/3000 bit/s or faster to/from the Deep Space Network's 70 m diameter antenna.
- Provided by: Spain.
X-band Low-Gain Antenna: Mars 2020 uses its low-gain antenna primarily for receiving signals. This antenna can send and receive information in every direction; that is, it is "omnidirectional." The antenna transmits at low data rate to the Deep Space Network antennas on Earth. Because it doesn’t need to be pointed, it provides a robust way to always communicate with the rover.
- Main function: Receiving antenna
- Radio frequency: X-band (7 to 8 GHz)
- Reception rates: Approximately 10 bit/s or faster from the Deep Space Network's 34 m diameter antennas or approximately 30 bit/s or faster from the Deep Space Network's 70 m diameter antenna.
Mars 2020 robotic arm
Mars 2020's robotic arm can move a lot like yours. It has a shoulder, elbow and wrist "joints" for maximum flexibility. The arm lets the rover work as a human geologist would: by holding and using science tools with its "hand" or turret. The rover's own "hand tools" extract cores from rocks, takes microscopic images and analyzes the elemental composition and mineral makeup of Martian rocks and soil. 12)
- Length: 2.1 m
- Degrees of freedom:
- There are five. They are made possible by tiny motors called "rotary actuators." The five degrees of freedom are known as the shoulder azimuth joint, shoulder elevation joint, elbow joint, wrist joint and turret joint.
- ”Hand” turret: At the end of the arm is the "turret." It's like a hand that carries scientific cameras, mineral and chemical analyzers for studying the past habitability of Mars, and choosing the most scientifically valuable sample to cache.
- Names of tools on the turret: SHERLOC and WATSON, PIXL, GDRT (Gaseous Dust Removal Tool), Ground Contact Sensor, Drill
- Drill: The drill is a rotary percussive drill designed to extract rock core samples from the surface of Mars.
- Drill bits: A suite of interchangeable bits: coring bits, regolith bit and an abrader.
- Main function: Assist in Mars surface investigation and sample collection
- Diameter of drilled holes: 27 mm.
The Mars 2020 mission will gather samples from Martian rocks and soil using its drill. The rover will then store the sample cores in tubes on the Martian surface. This entire process is called "sample caching". 13)
Mars 2020 will be the first mission to demonstrate this on Mars. It could potentially pave the way for future missions that could collect the samples and return them to Earth for intensive laboratory analysis.
The three major steps in sample handling are:
- Objectives: Collect and store a compelling set of rock and soil samples that could be returned to earth in the future.
- Witness tubes: 5 tubes
- Sample containers: 43 containers
- Samples to be collected: at least 20 samples
The Mars 2020 rover requires electrical power to operate. Without power, the rover cannot move, use its science instruments, or communicate with Earth.
Mars 2020 carries a radioisotope power system. This power system produces a dependable flow of electricity using the heat of plutonium's radioactive decay as its "fuel."
The power source is called the MMRTG (Multi-Mission Radioisotope Thermoelectric Generator). The MMRTG converts heat from the natural radioactive decay of plutonium into electricity. This power system charges the rover's two primary batteries. The heat from the MMRTG is also used to keep the rover's tools and systems at their correct operating temperatures.
The Department of Energy (DOE), in support of NASA, has developed several generations of such space nuclear power systems that can be used to supply electricity — and useful excess heat — for a variety of space exploration missions. The current RPS (Radioisotope Power System), called a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), was designed with the flexibility to operate on planetary bodies with atmospheres, such as at Mars, as well as in the vacuum of space. An MMRTG generates about 110 W of electrical power at launch, an increment of power that can be matched with a variety of potential mission needs. As with prior RPS, ensuring a high degree of safety is also a fundamental consideration. 14)
How RTGs work: RTGs work by converting heat from the natural decay of radioisotope materials into electricity. RTGs consist of two major elements: a heat source that contains the radioisotope fuel (mostly plutonium-238), and solid-state thermocouples that convert the plutonium’s decay heat energy to electricity.
Conversion of heat directly into electricity is a scientific principle discovered two centuries ago. German scientist Thomas Johann Seebeck observed that an electric voltage is produced when two dissimilar, electrically conductive materials are joined in a closed circuit and the two junctions are kept at different temperatures. Such pairs of junctions are called thermoelectric couples (or thermocouples).
The power output from such thermocouples is a function of the temperature of each junction and the properties of the thermoelectric materials. The thermocouples in RTGs use heat from the natural decay of the radioisotope fuel to heat the hot-side junction of the thermocouple, and the cold of space to produce a low temperature at the cold-side junction
Figure 8: Model of an MMRTG, including its internal General Purpose Heat Source (GPHS) modules (image credit: NASA)
- Objective: Provide electricity to the rover
- Location: Aft end of the rover
- Size: 64 cm in diameter by 66 cm long
- Mass: ~45 kg
- Power system: Uses 4.8 kg of plutonium dioxide as the source of the steady supply of heat
- Electrical power produced: About 110 W at launch, declining a few percent per year
- Batteries: Two lithium-ion rechargeable batteries to meet peak demands of rover activities when the demand temporarily exceeds the MMRTG's steady electrical output levels.
- Reliability: The electrical power system on the Mars 2020 rover is just like the one used on the Mars Science Laboratory Curiosity rover. NASA has used similar power systems reliably for decades, including the Apollo missions to the Moon, the Viking missions to Mars, and on spacecraft that flew to the outer planets and Pluto, including the Pioneer, Voyager, Ulysses, Galileo, Cassini, and New Horizons missions.
- Safety: Built with several layers of rugged protective material to contain its fuel in a wide range of potential launch accidents, verified through impact testing. The heat source plutonium is manufactured in a ceramic form, which helps it avoid being a significant health hazard unless broken into very fine pieces or vaporized, and then inhaled or swallowed. In the unlikely event of a Mars 2020 launch accident, those who might be exposed could receive an average dose of 15-60 millirem. A resident of the United States receives, on average, 310 millirem of radiation each year from natural sources, such as radon and cosmic rays from space.
This power system provides several advantages:
• The 14-year operational lifetime of an MMRTG provides significant reserve for Mars 2020 prime mission duration of 1.5 Mars years (three Earth years)
• It gives the rover greater mobility over a large range of latitudes and altitudes
• It allows scientists to maximize the capabilities of the rover's science instruments
• It provides engineers with a lot of flexibility in operating the rover (e.g., day and night, and through the winter season).
Note: As of July 2020, the previously single large Mars2020 file has been split into three files, to make the file handling manageable for all parties concerned, in particular for the user community. The chapter ”Development Status” has so high-resolution imagery, that it had to be split into two files.
• This file covers the Mars 2020 mission and its imagery without the Development Status
Launch: The Mars 2020 mission was launched from the Cape Canaveral Air Force Station (SLC-41) in Florida on July 30, 2020 (11:50 UTC) on a two-stage Atlas V-541 launch vehicle, provided by ULA (United Launch Alliance). The mission will land at the Jezero Crater on 18 February 2021. 15) 16)
- "With the launch of Perseverance, we begin another historic mission of exploration," said NASA Administrator Jim Bridenstine. "This amazing explorer's journey has already required the very best from all of us to get it to launch through these challenging times. Now we can look forward to its incredible science and to bringing samples of Mars home even as we advance human missions to the Red Planet. As a mission, as an agency, and as a country, we will persevere."
- The ULA Atlas V's Centaur upper stage initially placed the Mars 2020 spacecraft into a parking orbit around Earth. The engine fired for a second time and the spacecraft separated from the Centaur as expected. Navigation data indicate the spacecraft is perfectly on course to Mars.
Figure 9: A United Launch Alliance Atlas V rocket with NASA’s Mars 2020 Perseverance rover onboard launches from Space Launch Complex 41, Thursday, July 30, 2020, at Cape Canaveral Air Force Station in Florida. The Perseverance rover is part of NASA’s Mars Exploration Program, a long-term effort of robotic exploration of the Red Planet (image credit: NASA, Joel Kowsky)
The Mars 2020 spacecraft separated from the rocket’s Centaur upper stage 57 minutes after liftoff and five minutes after a second burn of the Centaur that placed the spacecraft on a trajectory toward Mars.
Perseverance is based on the Curiosity rover that has been on Mars since August 2012, but with a number of modifications. “We’re carrying about 50% more surface payload than Curiosity did, and that was by far the most complex thing we had ever done up until that time,” Matt Wallace, Mars 2020 deputy program manager, said at a pre-launch briefing.
Much of that additional payload, and complexity, is for the rover’s system to collect samples of Martian rocks. The rover will cache up to three dozen samples in tubes for return to Earth by two later missions that NASA is developing in cooperation with the European Space Agency for launch in 2026.
The rover includes several other upgrades. A terrain relative navigation system will compare images taken by the spacecraft during its descent to the Martian surface with maps on the spacecraft, and direct the spacecraft accordingly to enable a pinpoint landing. Engineers also upgraded the rover’s wheels after rocks damaged the wheels on Curiosity.
In addition to its payload of sample collection equipment and scientific experiments, Perseverance is carrying a small helicopter called Ingenuity. The 1.8-kilogram helicopter, stored on the rover’s belly pan, will be released after landing for a series of flight tests.
“We as human beings have never flown a rotorcraft outside of our Earth’s atmosphere, so this will be very much a Wright Brothers moment,” said Mimi Aung, Ingenuity Mars Helicopter project manager at JPL, during a pre-launch briefing. Engineers hope to perform several flights of Ingenuity over 30 days to test its performance.
Aung compared Ingenuity to Sojourner, the small rover flown on the Mars Pathfinder lander mission in 1997, paving the way for larger rovers like Perseverance. “This Mars helicopter, Ingenuity, could lead to the opening of a whole new way to explore,” she said.
• October 27, 2020: NASA's Mars 2020 Perseverance rover mission has logged a lot of flight miles since being lofted skyward on July 30 - 146.3 million miles (235.4 million km) to be exact. Turns out that is exactly the same distance it has to go before the spacecraft hits the Red Planet's atmosphere like a 11,900 mph (19,000 km/h) freight train on Feb. 18, 2021. 17)
- The Sun's gravitational influence plays a significant role in shaping not just spacecraft trajectories to Mars (as well as to everywhere else in the solar system), but also the relative movement of the two planets. So Perseverance's route to the Red Planet follows a curved trajectory rather than an arrow-straight path.
Work Continues En Route
- The mission team continues to check out spacecraft systems big and small during interplanetary cruise. Perseverance's RIMFAX and MOXIE instruments were tested and determined to be in good shape on Oct. 15. MEDA got a thumbs up on Oct. 19. There was even a line item to check the condition of the X-ray tube in the PIXL instrument on Oct. 16, which also went as planned.
- "If it is part of our spacecraft and electricity runs through it, we want to confirm it is still working properly following launch," said Keith Comeaux, deputy chief engineer for the Mars 2020 Perseverance rover mission. "Between these checkouts - along with charging the rover's and Mars Helicopter's batteries, uploading files and sequences for surface operations, and planning for and executing trajectory correction maneuvers - our plate is full right up to landing."
More About the Mission
- A key objective of Perseverance's mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the planet's geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).
- Subsequent missions, currently under consideration by NASA in cooperation with ESA (European Space Agency), would send spacecraft to Mars to collect these cached samples from the surface and return them to Earth for in-depth analysis.
- The Mars 2020 mission is part of a larger program that includes missions to the Moon as a way to prepare for human exploration of the Red Planet. Charged with returning astronauts to the Moon by 2024, NASA will establish a sustained human presence on and around the Moon by 2028 through NASA's Artemis lunar exploration plans.
• September 28, 2020: Perseverance is one of a few Mars spacecraft carrying laser retroreflectors. The devices could provide new science and safer Mars landings in the future. 18)
- When the Apollo astronauts landed on the Moon, they brought devices with them called retroreflectors, which are essentially small arrays of mirrors. The plan was for scientists on Earth to aim lasers at them and calculate the time it took for the beams to return. This provided exceptionally precise measurements of the Moon's orbit and shape, including how it changed slightly based on Earth's gravitational pull.
- Research with these Apollo-era lunar retroreflectors continues to this day, and scientists want to perform similar experiments on Mars. NASA's Perseverance rover – scheduled to land on the Red Planet on Feb. 18, 2021 – carries the palm-size Laser Retroreflector Array (LaRA). There's also small one aboard the agency's InSight lander, called Laser Retroreflector for InSight (LaRRI). And a retroreflector will be aboard the ESA (European Space Agency) ExoMars rover that launches in 2022.
- While there is currently no laser in the works for this sort of Mars research, the devices are geared toward the future: Reflectors like these could one day enable scientists conducting what is called laser-ranging research to measure the position of a rover on the Martian surface, test Einstein's theory of general relativity, and help make future landings on the Red Planet more precise.
- "Laser retroreflectors are shiny, pointlike position markers," said Simone Dell'Agnello, who led development of all three retroreflectors at Italy's National Institute for Nuclear Physics, which built the devices on behalf of the Italian Space Agency. "Because they're simple and maintenance-free, they can work for decades."
A Box of Mirrors
- The devices work a lot like a bike reflector, bouncing light back in the direction of its source. Perseverance's LaRA, for example, is a 2-inch-wide (5-cm-wide) dome speckled with half-inch holes containing glass cells. In each cell, three mirrored faces are positioned at 90-degree angles from one another so that light entering the holes is directed back out at exactly the same direction it came from.
- LaRA is much smaller than the retroreflectors on the Moon. The earliest ones, delivered by the Apollo 11 and 14 missions, are about the size of typical computer monitor and embedded with 100 reflectors; the ones delivered by Apollo 15 are even larger and embedded with 300 reflectors. That's because the lasers have to travel as much as 478,000 miles (770,000 km) to the Moon and back. By the return trip, the beams are so faint, they can't be detected by the human eye.
- The beams that Perseverance's LaRA and InSight's LaRRI were built to reflect would actually have a far shorter journey, despite Mars being some 249 million miles (401 million km) away at its farthest point from Earth. Rather than traveling back and forth from Earth, which would require enormous retroreflectors, the laser beams would just need to travel back and forth from a future Mars orbiter equipped with an appropriate laser.
Figure 10: Visible both in the inset photograph on the upper left and near the center of NASA's Perseverance Mars rover in this illustration is the palm-size dome called the Laser Retroreflector Array (LaRA). In the distant future, laser-equipped Mars orbiters could use such a reflector for scientific studies ( image credit: NASA/JPL-Caltech)
- Such an orbiter could determine the precise position of a retroreflector on the Martian surface. And since Perseverance will be mobile, it could provide multiple points of reference. Meanwhile, the orbiter's position would also be tracked from Earth. This would allow scientists to test Einstein's theory of general relativity, as they have with retroreflectors on the Moon. Each planet's orbit is greatly influenced by the bend in space-time created by the Sun's large mass.
- "This kind of science is important for understanding how gravity shapes our solar system, the whole universe, and ultimately the roles of dark matter and dark energy," Dell'Agnello noted.
- In the case of the InSight lander, which touched down on Nov. 26, 2018, laser-ranging science could also aid the spacecraft's core mission of studying Mars' deep interior. InSight relies on a radio instrument to detect subtle differences in the planet's rotation. In learning from the instrument how the planet wobbles over time, scientists may finally determine whether Mars' core is liquid or solid.
- And if the science team were able to use the lander's retroreflector, they could get even more precise positioning data than InSight's radio provides. LaRRI could also detect how the terrain InSight sits on shifts over time and in what direction, revealing how the Martian crust expands or contracts.
Better Landings on Mars
- Mars landings are hard. To help get Perseverance safely to the surface, the mission will rely on Terrain-Relative Navigation, a new technology that compares images taken during descent to an onboard map. If the spacecraft sees itself getting too close to danger (like a cliffside or sand dunes), it can veer away.
- But in such a mission-critical event, you can never have too many backups. Future missions barreling toward the surface of the Red Planet could use the series of reference points from laser retroreflectors as a check on the performance of their Terrain Relative Navigation systems – and perhaps even boost their accuracy down to a few centimeters. When the difference between successfully landing near an enticing geological formation or slipping down the steep slope of a crater wall can be measured in mere feet, retroreflectors might be critical.
- "Laser ranging could open up new kinds of Mars exploration," Dell'Agnello said.
• August 13, 2020: NASA's Ingenuity Mars Helicopter received a checkout and recharge of its power system on Friday, August 7, one week into its near seven-month journey to Mars with the Perseverance rover. This marks the first time the helicopter has been powered up and its batteries have been charged in the space environment. 19)
- During the eight-hour operation, the performance of the rotorcraft's six lithium-ion batteries was analyzed as the team brought their charge level up to 35%. The project has determined a low charge state is optimal for battery health during the cruise to Mars.
- "This was a big milestone, as it was our first opportunity to turn on Ingenuity and give its electronics a 'test drive' since we launched on July 30," said Tim Canham, the operations lead for Mars Helicopter at NASA's Jet Propulsion Laboratory in Southern California. "Since everything went by the book, we'll perform the same activity about every two weeks to maintain an acceptable state of charge."
- The 2 kg helicopter - a combination of specially designed components and off-the-shelf parts - is currently stowed on Perseverance's belly and receives its charge from the rover's power supply. Once Ingenuity is deployed on Mars' surface after Perseverance touches down, its batteries will be charged solely by the helicopter's own solar panel. If Ingenuity survives the cold Martian nights during its preflight checkout, the team will proceed with testing.
- "This charge activity shows we have survived launch and that so far we can handle the harsh environment of interplanetary space," said MiMi Aung, the Ingenuity Mars Helicopter project manager at JPL. "We have a lot more firsts to go before we can attempt the first experimental flight test on another planet, but right now we are all feeling very good about the future."
- The small craft will have a 30-Martian-day (31-Earth-day) experimental flight-test window. If it succeeds, Ingenuity will prove that powered, controlled flight by an aircraft can be achieved at Mars, enabling future Mars missions to potentially add an aerial dimension to their explorations with second-generation rotorcraft.
• July 30, 2020: European scientists will help select rocks and soil from Mars in the search for life on our planetary neighbor. 20)
- Five European researchers are part of NASA’s Mars 2020 science team to select the most promising martian samples bound for Earth.
- The mission to Mars launched today for its seven-month journey to the Red Planet. Once there, the team will guide the Perseverance rover as it hunts for evidence of ancient microbial life.
Figure 11: This video shows Jezero crater, the landing site of the NASA Mars 2020 Perseverance rover on the Red Planet, based on images from ESA’s Mars Express mission. The planned landing area is marked with an orange ellipse. The animation was created using an image mosaic made from four single orbit observations obtained by the High Resolution Stereo Camera (HRSC) on Mars Express between 2004 and 2008. The mosaic combines data from the HRSC nadir and color channels; the nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface. The mosaic image was then combined with topography information from the stereo channels of HRSC to generate a three-dimensional landscape, which was then recorded from different perspectives, as with a movie camera, to render the flight shown in the video. (video credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO ; Music: Björn Schreiner ; Soundtrack logo: Alicia Neesemann)
- The group is made up of researchers from Belgium, France, Sweden and the UK. “These top scientists from across Europe are experts on how to collect, analyze and read the history of the rocks under our feet. Now they will also have to anticipate the needs and challenges of working with martian samples returned to laboratories back on Earth,” says ESA’s Mars Sample Return acting program scientist Gerhard Kminek.
- For the next three years, the team will be at the core of a wider NASA team.
Figure 12: Geological detective Mark Sephton has built his career looking for molecular clues of past life. Organic geochemistry, or the forensic science of organic molecules in rocks, is a passion that this Professor at the Imperial College London in the UK is taking all the way to Mars (image credit: Imperial College London)
- Sandra Siljeström, from Sweden’s research institute RISE, dreams of having the “Bring it to me now!” feeling while remotely analyzing a rock spotted on Mars at the rover landing site – the Jezero crater. Sandra has more than a decade of expertise in organic geochemistry.
Figure 13: Sandra Siljeström in the lab in front of the ToF-SIMS, an spectrometer for surface analysis using a pulsed ion beam (photo: S. Siljeström)
- The area of the Jezero crater contains sediments of an ancient river delta, where evidence of past life could be preserved if it ever existed on the planet.
- Once the Perseverance rover retrieves samples of rock and soil from Mars, it will seal them in canisters and drop them on the surface to be collected by a future retrieval mission.
- “The Mars 2020 mission is the first step for the ultimate martian challenge: the Mars Sample Return campaign. NASA and ESA aim to deliver the material from the martian surface to Earth by 2031,” adds Gerhard.
- To bring Mars samples to Earth, three carefully timed missions are required.
- NASA will deliver the ESA Sample Fetch Rover to the vicinity of the Mars 2020 landing site. This European rover will autonomously track down and collect up to 36 sample tubes deposited by Perseverance, and take them to NASA’s Mars Ascent vehicle.
Figure 14: Overview of the ESA–NASA Mars Sample Return mission. Bringing samples from Mars is the logical next step for robotic exploration and it will require multiple missions that will be more challenging and more advanced than any robotic missions before. Accomplishments in robotic exploration in recent years have increased confidence in success – multiple launches will be necessary to deliver samples from Mars. ESA is working with NASA to explore mission concepts for an international Mars Sample Return campaign between 2020 and 2030. — Three launches will be necessary to accomplish landing, collecting, storing and finding samples and delivering them to Earth. NASA’s Mars 2020 mission will explore the surface and rigorously document and store a set of samples in canisters in strategic areas to be retrieved later for flight to Earth. Two subsequent missions are foreseen to achieve this next step (image credit: ESA, K. Oldenburg)
Sensor complement of the MARS 2020 Rover (MastCam-7, SuperCam, PIXL, SHERLOC, MOXIE, MEDA, RIMFAX)
Scientists will use the Mars 2020 rover to identify and select a collection of rock and soil samples that will be stored for potential return to Earth by a future mission. The Mars 2020 mission is responsive to the science objectives recommended by the National Research Council's 2011 Planetary Science Decadal Survey.
Figure 15: This 2015 diagram shows components of the investigations payload for NASA's Mars2020 rover (image credit: NASA) 23)
MastCam-Z (Mast-mounted Camera system)
Mastcam-Z is an advanced camera system with panoramic and stereoscopic imaging capability with the ability to zoom. The instrument also will determine mineralogy of the Martian surface and assist with rover operations. The principal investigator is James Bell, ASU (Arizona State University) in Tempe. The instrument is based on the successful Mastcam instrument on NASA's Mars Curiosity rover. Mastcam-Z will be the main eyes of NASA's next Mars rover. 24)
From its position on the Mars-2020 Remote Sensing Mast (RSM), the Mastcam-Z imaging investigation acquires visible color (RGB), stereo panoramas of the Martian surface at resolutions sufficient to resolve ~1 mm features in the near-field (robotic arm workspace) and ~3-4 cm features 100 meters away. Mastcam-Z is also equipped with bandpass filters (400 - 1000 nm) that are used to distinguish unweathered from weathered materials and to provide important insights into the mineralogy of many silicates, oxides, oxyhydroxides, and diagnostic hydrated minerals. Mastcam-Z also images the sun directly using a pair of solar filters.
The Mastcam-Z cameras have the capability to zoom, focus, acquire data at high-speed (video rates of 4 frames/sec or faster for subframes), and store large amounts of data in internal storage. These capabilities permit investigators to examine targets that are otherwise out of the rover's reach. The cameras can observe time-dependent phenomena such as dust devils, cloud motions, and astronomical phenomena, as well as activities related to driving, sampling, and caching. Mastcam-Z has improved stereo imaging capabilities compared to the Mars Science Laboratory rover's Mastcam and the Mars Exploration Rovers' Pancam. Mastcam-Z provides important advances in navigational and instrument-placement capabilities that help support and enhance the Mars 2020 rover's driving and coring/sampling capabilities.
Figure 16: MastCam-Z lens packaging (image credit: NASA/JPL Caltech, ASU, MSSS)
Mastcam-Z observes textural, mineralogical, structural, and morphologic details in rocks and fines at the rover's field site. The cameras allow the science team to piece together the geologic history of the site via the stratigraphy of rock outcrops and the regolith, as well as to constrain the types of rocks present (e.g., sedimentary vs. igneous). The Mastcam-Z cameras also document dynamic processes and events via video (e.g., dust devils, cloud motions, and astronomical phenomena, as well as activities related to driving, sampling, and caching), observe the atmosphere, and contribute to rover navigation and target selection for investigations by the coring/caching system, as well as other instruments.
- Objectives: To take high-definition video, panoramic color and 3D images of the Martian surface and features in the atmosphere with a zoom lens to magnify distant targets.
- Location: Mounted on the rover mast at the eye level, 2 meters tall. The cameras are separated by 24.2 cm to provide stereo vision.
- Mass: ~4g
- Power: ~17.4 W
- Volume: Camera head, per unit: 11 x 12 x 26 cm; Digital electronics assembly: 22 x 12 x 5 cm; Calibration target: 10 x 10 x 7 cm.
- Data return: ~ 148 Mbit/sol on average
- Color quality: Similar to that of a consumer digital camera (2-megapixel)
- Image size: 1600 x 1200 pixels max
- Image resolution: Able to resolve between about 150 µm/pixel to 7.4 mm/pixel depending on distance.
SuperCam, an instrument that can provide imaging, chemical composition analysis, and mineralogy. The instrument will also be able to detect the presence of organic compounds in rocks and regolith from a distance. The principal investigator is Roger Wiens, Los Alamos National Laboratory, Los Alamos, New Mexico. This instrument also has a significant contribution from the Centre National d'Etudes Spatiales,Institut de Recherche en Astrophysique et Plane'tologie (CNES/IRAP) France.
SuperCam is a remote-sensing instrument for the Mars 2020 mission that uses remote optical measurements and laser spectroscopy to determine fine-scale mineralogy, chemistry, and atomic and molecular composition of samples encountered on Mars. 25) 26)
To enable these measurements, SuperCam is, in fact, many instruments in one.
• For measurements of elemental composition, it integrates the remote Laser Induced Breakdown Spectroscopy (LIBS) capabilities of the highly successful ChemCam instrument included in the payload of the Curiosity rover currently exploring Mars. LIBS uses a 1064 nm laser to investigate targets up to 7 m distance from the rover.
• In addition, SuperCam also performs Raman spectroscopy (at 532 nm to investigate targets up to 12 m distance from the rover), Time-Resolved Fluorescence (TRF) spectroscopy, Visible and InfraRed (VISIR) reflectance spectroscopy (400 – 900 nm, 1.3 – 2.6 µm) at a distance in order to provide information about the mineralogy and molecular structure of samples under consideration, as well as being able to search directly for organic materials.
• Finally, SuperCam also acquires high-resolution images of samples under study using a color remote micro-imager (RMI). The collection of data provided by this suite of correlated measurements on a sample can be used to determine directly the geochemistry and mineralogy of samples.
SuperCam measurements can be rapidly acquired without the need to position the rover or rover arm upon the target, facilitating rapid and efficient measurements during Mars operations. As demonstrated by ChemCam, the SuperCam laser can be used to "blast off" dust from surfaces at a distance in order to get a better look at solid surfaces on Mars, without having to drive up to samples and perform manipulations with the rover arm or associated tools.
SuperCam is a continuing effort between Los Alamos and the IRAP research institution in Toulouse, France, and the French Space Agency (CNES), with additional collaboration from the University of Hawaii and the University of Valladolid (UVA) in Spain.
- Objectives: To identify the chemical composition of rocks and soils, including their atomic and molecular makeup
- Location: The SuperCam instrument is mounted on the "head" of the rover's long-necked mast.
- Mass: The mast-mounted sensor head has a mass of 5.6 kg, the Rover body-mounted electronics have a mass of 4.8 kg. The calibration target has a mass of 0.2 kg.
- Power: 17.9 W.
- Volume: The volume of the Mast-mounted sensor head is 38 x 24 x 19 cm.
- Calibration target: 3 cm in size.
- Data return: 15.5 Mbit per experiment or about 4.2 Mbit per day.
SuperCam's laser is uniquely capable of remotely clearing away surface dust, giving all of its instruments a clear view of the targets.
Figure 17: Mars 2020's mast, or "head," includes a laser instrument called SuperCam that can vaporize rock material and study the resulting plasma (image credit: NASA/JPL-Caltech)
PIXL (Planetary Instrument for X-ray Lithochemistry)
PIXL is an X-ray fluorescence spectrometer that will also contain an imager with high resolution to determine the fine scale elemental composition of Martian surface materials. PIXL will provide capabilities that permit more detailed detection and analysis of chemical elements than ever before. The principal investigator is Abigail Allwood, NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. 27)
The PIXL for the Mars-2020 rover is a microfocus X-ray fluorescence instrument that rapidly measures elemental chemistry at sub-millimeter scales by focusing an X-ray beam to a tiny spot on the target rock or soil and analyzing the induced X-ray fluorescence.
Scanning the beam reveals spatial variations in chemistry in relation to fine-scale geologic features such as laminae, grains, cements, veins, and concretions (Figure 18).
The high X-ray flux enables high sensitivity and short integration times: most elements are detected at lower concentrations than possible on previous landed payloads to Mars, and several new elements can be detected that were not previously detectable on these missions. Fast acquisition allows rapid scanning so that PIXL reveals the associations between different elements and the observed textures and structures. The same spectra can be summed for bulk analysis, allowing comparison with bulk chemistry measurements at sites previously explored on Mars. With PIXL’s simple design comes operational efficiency and experimental flexibility—an instrument that can adapt to different scientific opportunities to produce a diverse set of scientifically powerful data products within the constraints of the mission.
Figure 18: PIXL breadboard maps of a paleoarchean altered conglomerate with unconformity surface, revealing complex lithology including rounded pyrite, chromite, zircon, K-Al-Cr clay in the fuchsitic mudstone, Mn,Fe,Ca-carbonate in alteration vein, silicification of the conglomerate matrix. Map size is 20 mm by 10 mm with a step size of 0.15 mm (image credit: NASA/A. Allwood)
The instrument consists of a main electronics unit in the rover’s body and a sensor head mounted on the robotic arm. The sensor head includes an x-ray source, X-ray optics, X-ray detectors, and high-voltage power supply (HVPS), as well as a micro-context camera (MCC) and light-emitting diode (LED). The PIXL can detect elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Y, Ga, Ge, As, and Zr, with important trace elements such as Rb, Sr, Y and Zr detectable at 10’s ppm level. An example is shown in Figure 19.
Figure 19: This Figure demonstrates that the PIXL instrument detects important trace elements (red) at 10's ppm. Insert: Rb, Sr, Y, Zr are clearly detected due to the lack of interfering excitation lines at 13-17 keV in PIXL (continuum subtracted using a modeled fit to Bremsstrahlung), image credit: NASA/JPL-Caltech
The advantages of the PIXL instrument are:
• High spatial resolution with a 0.12 mm-diameter beam enabling sub-mm scale geochemistry correlated with texture
• Spatial coverage, targeting and position knowledge: fine step size and micro-context camera will provide resolution and footprint at hand-lens scale
• Fast spectral acquisition: measure most major and minor elements at 0.5 wt% in 5 seconds.
• Large range of detectable elements (26+ elements)
• High sensitivity: detect important trace elements at 10’s ppm level
• Operational efficiency: The combined effect of PIXL’s speed, sensitivity, resolution, coverage/targeting, and measurement flexibility allows PIXL to search efficiently and locate the places of interest and to observe small patches of clean rock
• Operational robustness: tolerant to surface roughness.
- Objectives: To measure the chemical makeup of rocks at a very fine scale
- Location: Mounted on the turret at the end of the robotic arm
- Mass: Arm-mounted sensor head: 4.3 kg; Body-mounted electronics: 2.6 kg; Calibration target: 0.015 kg
- Power: ~25 W
- Volume: Arm-mounted sensor head: 21.5 x 27 x 23 cm
- Calibration targets: Diameter of each of four disks: 5 mm; Pedestal base: 39 x 30 mm
- Data return: About 16 Mbit/experiment or about 2 MB/day.
If you are looking for signs of ancient life, you want to look at a small scale and get detailed information about chemical elements present.
SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals)
SHERLOC is a spectrometer that will provide fine-scale imaging and uses an ultraviolet (UV) laser to determine fine-scale mineralogy and detect organic compounds. SHERLOC will be the first UV Raman spectrometer to fly to the surface of Mars and will provide complementary measurements with other instruments in the payload. The principal investigator is Luther Beegle, NASA/JPL. "Key, driving questions are whether Mars is or was ever inhabited, and if not, why not? The SHERLOC investigation will advance the understanding of Martian geologic history and identify its past biologic potential." 28)
SHERLOC is an arm-mounted, Deep UV (DUV) resonance Raman and fluorescence spectrometer utilizing a 248.6 nm DUV laser and <100 µm spot size. The laser is integrated to an autofocusing/scanning optical system, and co-boresighted to a context imager with a spatial resolution of 30 µm.
SHERLOC enables non-contact, spatially resolved, and highly sensitivity detection and characterization of organics and minerals in the Martian surface and near subsurface. The instrument goals are to assess past aqueous history, detect the presence and preservation of potential biosignatures, and to support selection of return samples. To do this, SHERLOC measures CHNOPS-containing mineralogy, measures the distribution and type of organics preserved at the surface, and correlates them to textural features.
SHERLOC operates over a 7 x 7 mm area through use of an internal scanning mirror. The 500 µm depth of view, in conjunction with the MAHLI heritage autofocus mechanisms, enables arm placements from 48 mm above natural or abraded surfaces without the need for rover arm repositioning/movement. Additionally, borehole interiors, after sample core removal, can be analyzed as a proxy for direct core analysis.
In addition to the combined spectroscopic and macro imaging component, SHERLOC also integrates a “second-eye” with a near-field-to-infinity imaging component called WATSON (Wide Angle Topographic Sensor for Operations and eNgineering), which is used for engineering science operations and science imaging. WATSON is a build-to-print camera based on the MSL (Mars Science Laboratory) Mars Hand Lens Imager (MAHLI). Integration is enabled by existing electronics within SHERLOC.
Deep UV-induced native fluorescence is very sensitive to condensed carbon and aromatic organics, enabling detection at or below 10-6 w/w (1 ppm) at <100 µm spatial scales. SHERLOC's deep UV resonance Raman enables detection and classification of aromatic and aliphatic organics with sensitivities of 10-2 to below 10-4 w/w at <100 µm spatial scales. In addition to organics, the deep UV Raman enables detection and classification of minerals relevant to aqueous chemistry with grain sizes below 20 µm grains.
SHERLOC's investigation combines two spectral phenomena, native fluorescence and pre-resonance/resonance Raman scattering. These events occur when a high-radiance, narrow line-width, laser source illuminates a sample. Organics that fluoresce absorb the incident photon and reemit at a higher wavelength. The difference between the excitation wavelength and the emission wavelength indicates the number of electronic transitions, which increases with increasing aromatic structures (i.e. number of rings). This phenomenon is highly efficient, with a typical cross section 105x greater than Raman scattering, and enables a powerful means to find trace organics.
The native fluorescence emission of organics extends from ~270 nm into the visible. This is especially useful, because it "creates" a fluorescence-free region (from 250 – 270 nm) where Raman scattering can occur. With SHERLOCs narrow-linewidth 248.6 nm DUV laser, additional characterization by Raman scattering from aromatics and aliphatic organics and minerals can be observed. Furthermore, excitation with a DUV wavelength enables resonance and pre-resonance signal enhancements (>100 to 10,000 x) of organic/mineral vibrational bonds by coupling of the incident photon energy to the vibrational energy. This results in high-sensitivity measurements, with low backgrounds, without the need of high-intensity of lasers, and avoids damage or modification of organics by inducing reactions with species such as perchlorates.
SHERLOC Ops: An Example Measurement on Fig Tree
Using the SHERLOC testbed, an analysis of a piece of the astrobiologically interesting chert obtained from the Fig Tree Group is shown.
A context image of the sample is acquired. Using the internal scanning mirror, a 50-micron laser spot is systematically rastered over the surface. On the same CCD, spectra in the range 250-360 nm are obtained. Analysis of the fluorescence region (>270 nm) identifies regions where organic material is present. Analysis of the fluorescence spectra identifies number of aromatic rings present, and identifies regions of high organic content. In order to achieve higher specificity, a longer integration can be used to collect deep UV Raman spectra. The Raman spectra shown on the right are from the two circles shown in the context image.
By studying the fluorescence and Raman data we can conclude that our analysis indicates that:
• The chert has not been altered uniformly — pressure/temperature exposures are evident from carbon maturity variation.
• The majority of matrix is thermally mature carbon — anthracitic to sub-bituminous.
• An intrusion of silica with much younger carbon invaded the main matrix.
Potential for biosignature preservation in the matrix is low due to thermal history of the sample, with high preservation in the thermally unaltered vein material.
- Objective: Fine-scale detection of minerals, organic molecules and potential biosignatures
- Location: SHERLOC is mounted on the turret at the end of the robotic arm
- Mass: The turret is 3.11 kg; the body is 1.61 kg
- Power: The turret consumes 32.2 W, the body 16.6 W
- Volume: 26.0 x 20.0 x 6.7 cm
- Data return: 79.7 Mbit (raw)
- Spatial resolution: Context imager: 30 µm; Laser: 50 µm
- FOV (Field of View): Imaging: 2.3 x 1.5 cm; Spectroscopy: 7 x 7 mm.
Key, driving questions are whether Mars is or was ever inhabited, and if not, why not? The SHERLOC investigation will advance the understanding of Martian geologic history and identify its past biologic potential.
Figure 20: Calibration target for the Mars 2020 SHERLOC instrument (image credit: NASA/Johnson Space Center) 29)
The SHERLOC instrument will be used to detect chemicals on the Martian surface that are linked to the existence of life. To keep the instrument working well, a team from the Astromaterials Research and Exploration Science (ARES) division at NASA’s Johnson Space Center (JSC) recently built a new calibration device for the rover to check SHERLOC’s function and properly tune it during the upcoming mission.
“SHERLOC is pretty complicated, and we came up with a list of 11 things that all have to be calibrated on this instrument,” said Marc Fries, ARES planetary scientist and Mars 2020 instrument co-investigator. “This sophisticated calibration device is also going to be used for a lot of other scientific and engineering investigations, and we’re really excited that it’s JSC’s contribution to the Mars 2020 rover.”
SHERLOC is mounted on the end of the rover's 2.1 m robotic arm and includes a laser, camera and chemical analyzers, called spectrometers. The sensitive components will be used together to search for substances that have been altered by water and possibly reveal evidence of past microscopic life on Mars.
“The rover’s scientific instruments go through all sorts of harsh conditions from the time they leave the lab until they arrive on the surface of Mars. SHERLOC needed a way to make sure it still operates as expected once it’s on the surface and throughout the duration of the mission,” said Trevor Graff, a scientist from Jacobs who works for ARES.
The solution was to create the calibration target, or “cal target” for short. The device is approximately the size of a large cell phone and mounted on the front of the rover. On its face are 10 “targets,” which consist of samples of different materials. The idea is that researchers will occasionally check SHERLOC’s function by directing it to scan the different materials on the cal target. The researchers will already know what the readings on those materials should be when SHERLOC is working correctly. If the actual readings are off, they’ll make adjustments to SHERLOC to get it set properly, or know to compensate for the errors when they analyze the data later.
Figure 21: Image of engineers with the Mars 2020 SHERLOC Calibration Target in a clean room at NASA/JSC (Johnson Space Center). This is the first Mars flight hardware that has been designed, assembled & tested at NASA/JSC, led by Jacobs/JETS Chief Scientist Trevor Graff. It will carry the first space suit materials to Mars and will carry a piece of a martian meteorite back to the surface of Mars (image credit: NASA/JSC) 30)
Science on the Side
In addition to tuning SHERLOC, the targets on the calibration device are serving double duty in other tests and experiments. For example, a number of the targets hold spacesuit materials that could one day be used to protect astronauts exploring Mars. SHERLOC’s scans of those materials will not only help tune the instrument, but measure how the advanced fabrics and other suit materials will hold up in the Martian environment, too.
“We also plan to build a small Mars exposure instrument here at JSC, and match the conditions inside it with weather data from the rover,” Fries said. “We’ll then place an identical set of spacesuit samples inside the chamber and periodically remove them to, for example, test the strength of fabrics or the clarity of helmet visor plastics. The result is we’ll be able to test spacesuit materials in Mars-like conditions long before astronauts ever go there.”
Another target contains an actual sample of a meteorite ejected from Mars long ago and discovered on Earth in 1999. Researchers plan to closely watch the rock sample to see how the Martian environment alters it over time, which will help them understand the chemical interactions between the planet’s surface and its atmosphere.
Finally, the target includes the first off-planet “cache” for geocaching enthusiasts to locate, with more details on that to be released soon.
MOXIE (Mars Oxygen ISRU Experiment)
MOXIE is an exploration technology investigation that will produce oxygen from Martian atmospheric carbon dioxide. The principal investigator is Michael Hecht, MIT (Massachusetts Institute of Technology), Cambridge, Massachusetts.
"When we send humans to Mars, we will want them to return safely, and to do that they need a rocket to lift off the planet. Liquid oxygen propellant is something we could make there and not have to bring with us. One idea would be to bring an empty oxygen tank and fill it up on Mars."
NASA is preparing for human exploration of Mars, and the MOXIE investigation on the Mars 2020 mission aims to address key knowledge gaps, including: 31)
• demonstration of In-Situ Resource Utilization (ISRU) technologies to enable propellant and consumable oxygen production from the Martian atmosphere, and
• characterization of atmospheric dust size and morphology to understand its effects on the operation of surface systems.
MOXIE collects CO2 from the Martian atmosphere, then electrochemically splits the CO2 molecules into O2 and CO. The O2 is then analyzed for purity before being vented back out to the Mars atmosphere along with the CO and other exhaust products.
Figure 22 shows the MOXIE functional block diagram. The CO2 Acquisition and Compression (CAC) system pulls Martian atmosphere from outside the Rover through a filter and pressurizes it to ~1 atmosphere. The pressurized CO2 gas is then regulated and fed to the Solid OXide Electrolyzer (SOXE), where it is electrochemically split at the cathode to produce pure O2 at the anode, a process equivalent to running a fuel cell in reverse.
The SOXE operates at 800° C, requiring a sophisticated thermal isolation system, including input gas preheating and exhaust gas cooling. There are O2 exhaust and CO2/CO exhaust streams, which are then analyzed to verify O2 production rate and purity and for process control. The electrical current through the SOXE is a direct result of the oxide ions transported across the electrolyte, and provides an independent measurement of O2 production rate.
Based on conversion efficiency calculated from flow rates and composition measurements, SOXE control parameters such as CO2 input flow rate, temperature, and applied voltage are used to optimize O2 production under Mars environmental conditions. The cooled exhausts are then filtered to satisfy planetary protection requirements and vented from the Rover. Process telemetry is reported to the Rover for downlink.
- Objective: To produce oxygen from the Martian carbon-dioxide atmosphere
- Power: 300 W
- Volume: 23.9 x 23.9 x 30.9 cm
- Oxygen production rate: About 10 grams per hour
- Operation time: Approximately two hours of oxygen (O2) production per experiment, which will be scheduled intermittently over the duration of the mission.
MEDA (Mars Environmental Dynamics Analyzer)
MEDA is a set of sensors that will provide measurements of temperature, wind speed and direction, pressure, relative humidity and dust size and shape. The principal investigator is Jose Rodriguez-Manfredi, Centro de Astrobiologia, Instituto Nacional de Tecnica Aeroespacial, Spain. 32)
MEDA is a suite of environmental sensors designed to record dust optical properties and six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and radiation in discrete bands of the UV, visible, and IR ranges of the spectrum.
The radiation sensor is part of an assembly with two arrays of photodiodes that also capture low elevation angle scattered light and a sky-pointing camera; these data are combined to characterize the properties of atmospheric aerosols.
Systematic measurement is the main driver for MEDA operations. Over the entire mission's lifetime, with a configured cadence and frequency in accordance to resource availability, MEDA records data from all sensors. Implementation of this strategy is based on a high degree of autonomy in MEDA operations. MEDA wakes itself up each hour and after recording and storing data, goes to sleep independently of rover operations. It records data whether the rover is awake or not, and both day and night.
The main science objectives for the science team are:
• Signature of the Martian general and mesoscale circulation on phenomena near the surface (e.g., fronts, jets)
• Microscale weather systems (e.g., boundary layer turbulence, heat fluxes, eddies, dust devils)
• Local hydrological cycle (e.g., spatial and temporal variability, diffusive transport from regolith)
• Dust optical properties, photolysis rates, ozone column, and oxidant production.
As an environmental instrument, MEDA's different sensors are in direct contact and exposed to the ambient:
• The radiation/dust sensor assembly is located on top of the rover deck.
• The pressure sensor is located inside the rover body and connected to the atmosphere through a dedicated pipe.
• All other sensors are located around the Remote Sensing Mast (RSM):
- Two wind sensor booms oriented at 120 degrees from each other measure winds approaching the RSM,
- Five sets of thermocouples measure the air temperature
- A thermal infrared sensor measures downward and upward thermal infrared radiation as well as surface skin temperature.
- The relative humidity sensor is also attached to the RSM.
The full set of sensors is controlled by the Instrument Control Unit (ICU) inside the rover body.
A suite of sensors to characterize the Martian low atmosphere and dust properties:
• Air temperature: Located around the RSM are three air temperature sensors (ATS). Two more are on the rover body to ensure that one of them is upwind. Placed on small thermal inertia forks, and outside the rover thermal boundary layers, these five sets of three thermocouples measure atmospheric temperature. The measurement range is 150 to 300 K, with a required accuracy of 5 K and a resolution of 0.1 K.
• Humidity: Located at the RSM inside a protecting cylinder, a humidity sensor (HS) measures the relative humidity with an accuracy of 10% in the 200-323 K range and with a resolution of 1%. A dust filter surrounds the cylinder to protect the sensor from dust deposition.
• Pressure: Located inside the rover body and connected to the external atmosphere via a tube, a pressure sensor (PS) collects pressure measurements. The tube exits the rover body through a small opening with protection against dust deposition. Its measurement range goes from 1 to 1150 Pa with an end-of-life accuracy of 20 Pa (calibration tests give values around 3 Pa) and a resolution of 0.5 Pa. As this component is in contact with the atmosphere, a HEPA filter is placed on the tube inlet to avoid contaminating the Martian environment.
• Radiation & dust: Located on the rover deck, the radiation and dust sensor (RDS) is composed of eight upward looking photodiodes in the following ranges:
- 255 ± 5 nm for the O3 Hartley Band center,
- 295 ± 5 nm for the O3 Hartley Band edge,
- 250-400 nm for total UV,
- 450±40 nm for MastCam-Z cross-calibration,
- 650 ± 25 nm for SuperCam cross-calibration,
- 880 ±5 nm for MastCam-Z cross-calibration,
- 950 ± 50 nm for NIR, and
- one panchromatic (at least 300-1000 nm) filter, with an accuracy better than 8% of the full range for each channel, computed based on Mars radiation levels and minimum dust opacity.
The photodiodes face the zenith direction and have a field of view of 30 degrees except for the panchromatic one with its 180º field of view.
A second array of side-looking photodiodes at 880 nm characterizes the low angle light scattering at different azimuth angles. They cover at least 270º or a circle with fields of view of ±15º and separated about 45º from each other.
A dedicated camera with ±60º around the zenith measures the intensity of the solar aureole.
The assembly of photodiodes and camera are placed on the rover deck without any dust protection. To mitigate dust degradation, magnetic rings are placed around each photodiode with the aim of maximizing their operational time. Nevertheless, to evaluate dust deposition degradation, images of the sensor are recorded periodically, with their readings compared with opacities from other Mars 2020 optical instruments such as MastCam-Z. A comparison of the differences in estimated sky opacities between MEDA and MastCam-Z permits evaluations of the level of dust deposition.
• Thermal radiation: Attached to the RSM and pointing to the front right side of the rover, the thermal infrared sensor (TIRS) measures the net infrared thermal radiation near the surface of Mars with a set of five thermopiles:
- three downward-pointing thermopiles with bands 16-20, 6.5-cut-on and 8-14 µm, and
- two upward-pointing thermopiles with bands 6.5-cut-on and 14.5-15.5 µm.
• Wind: Attached to the RSM, two wind sensors (WS) measure wind speed and direction. These magnitudes are derived based on the information provided by six two-dimensional detectors on each boom. The detectors are located on six boards 60 degrees apart around the boom axis. Each records local speed and direction in the plane of the board. The combination of the 6 boards per boom serves to determine wind speed, as well as pitch and yaw angle of each boom relative to the flow direction.
The requirement is to determine horizontal wind speed with 2 m/s accuracy in the range of 0 to 40 m/s, with a resolution of 0.5 m/s. The directional accuracy is expected to be better than 22.5 degrees. For vertical wind, the range is 0 to 10 m/s, and the accuracy and resolution are the same as for horizontal wind.
The booms hold the detectors out of the RSM's thermal boundary layer, aiming to minimize the wind flow perturbation by the RSM at the boom tip where the these detectors are located. The two booms are separated in azimuth to help ensure that at least one of them will record clean wind data when the other is in the wake of the rover.
To correct for the perturbations at the booms by the RSM and the rover on the environmental temperature and wind field, a variety of numerical analyses and wind tunnel tests are used during calibration under Mars conditions. Numerical simulations are used to obtain results where tests conditions cannot be reproduced on Earth.
- Objectives: To measure weather and monitor dust with sensors from the surface of Mars
- Location: Sensors are located on the rover's mast "neck" and on the deck, front and interior of the rover's body
- Mass: Approximately 5.5 kg for all components
- Power: Up to 17 W, depending on scheduled measurements
a) Air temperature sensors: Each of five sensors is 5.75 x 2.75 x 6.75 cm
b) Radiation and dust sensor: 13.2 x 11.5 x 12.5 cm
c) Relative humidity sensor: 6.25 x 5.75 x 5.75 cm
d) Wind sensors: Wind Sensor 1 is 5 x 17 cm, wind sensor 2 is 5 x 40 cm
e) Instrument control unit and pressure sensor: 14 x 14 x 13 cm
- Data return: Approximately 11 MB.
MEDA will help prepare for human exploration by providing daily weather report and information on the radiation and wind patterns on Mars.
RIMFAX (The Radar Imager for Mars' Subsurface Exploration)
RIMFAX is a ground-penetrating radar that will provide centimeter-scale resolution of the geologic structure of the subsurface. The principal investigator is Svein-Erik Hamran of FFI (Norwegian Defence Research Establishment), Norway.
"No one knows what lies beneath the surface of Mars. Now, we'll finally be able to see what's there."
RIMFAX builds on mature tried-and-true GPR technology used on Earth for a wide variety of scientific and engineering applications, adapted for use in a rover platform on the surface of Mars. Its ultra wideband design, operating from 150 MHz to 1.2 GHz, affords a theoretical limit of 14.2 cm for vertical (range) resolution in free-space. The instrument is composed of an electronics box, installed within the interior of the rover, and a nadir-point antenna affixed to the exterior (rear) of the rover. 33)
RIMFAX will operate as the rover drives and will be commanded to produce individual soundings in different modes, where some modes are for shallow and others are for deep penetration. The default operation will produce interleaved pairs of shallow- and deep-soundings at every 10 cm along a rover traverse. The expectation is for RIMFAX signals to achieve penetrations of 10 m, but it may well exceed that for subsurface conditions that are friendly to the propagation of radar waves.
The overarching goal of RIMFAX is to image the subsurface structure and constrain the nature of the material underlying the landing site. This is made possible because the propagation of radar waves is sensitive to the dielectric properties of materials, such that variations in composition and porosity across geologic strata yield radar reflections that can be identified, mapped, and interpreted in the geological sense.
Specifically, RIMFAX supports and enhances the Mars 2020 investigation in the following, but not limited, ways:
• Assess the depth and extent of regolith;
• Detect different subsurface layers and their relationship to visible surface outcrops;
• Characterize the stratigraphic section from which a cored-and-cached sample derives, including crosscutting relations and features indicative of past environments.
Figure 23: Sample radargram of a glacier in Svalbard obtained with the HUBRA radar instrument, a precursor of RIMFAX built by the FFI team (image credit: NASA, FFI)
Figure 24: Photo showing the prototype RIMFAX antenna attached to a snowmobile during tests in Svalbard, Norway (image credit: NASA/JPL-Caltech, FFI)
- Objective: To see geologic features under the surface with ground-penetrating radar
- Location: The radar antenna is on the lower rear of the rover
- Mass: < 3 kg
- Power: 5-10 W
- Volume: 196 x 120 x 66 mm
- Data return: 5 to 10 kB per sounding location
- Frequency range: 150 to 1200 MHz
- Vertical resolution: As small as about 7.5 - 30 cm thick
- Penetration depth: > 10 m deep depending on materials
- Measurement interval: About every 10 cm along the rover track.
NASA's Mars 2020 mission uses the NASA's Deep Space Network (DSN), an international network of antennas that provides communication links between planetary exploration spacecraft and their mission teams on Earth. 34)
The DSN consists of three deep-space communications complexes placed approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. This strategic placement permits constant links to distant spacecraft even as the Earth rotates on its own axis.
As with previous Mars landers and rovers, the Mars 2020 mission relies on Mars-orbiting spacecraft to relay data from the rover to the antennas of the Deep Space Network.
Figure 25: The Goldstone 70 m antenna tracks under a full moon (image credit: NASA)
3) ”Mars 2020,” NASA Facts, June 2015, URL: https://mars.nasa.gov/mars2020/files/mars2020/Mars2020_Fact_Sheet.pdf
5) ”Mars 2020 Mission Contributions to NASA's Mars Exploration Program Science Goal,” NASA, URL: https://mars.nasa.gov/mars2020/mission/science/goals/
8) ”Rover body,” NASA, URL: https://mars.nasa.gov/mars2020/mission/rover/body/
11) ”Mars 2020 Mission Communications,” NASA, URL: https://mars.nasa.gov/mars2020/mission/rover/communications/
”NASA, ULA Launch Mars 2020 Perseverance Rover Mission to Red
Planet,” NASA Press Release 2020-077, 30 July 2020, URL: https://www.nasa.gov/press-release/
16) Jeff Foust, ”Atlas 5 launches Mars 2020 mission,” Space News, 30 July 2020, URL: https://spacenews.com/atlas-5-launches-mars-2020-mission/
17) ”NASA's Perseverance Rover Is Midway to Mars,” NASA/JPL News, 27 October 2020, URL: https://www.jpl.nasa.gov/news/news.php?feature=7770&utm_source=iContact&
18) ”NASA's New Mars Rover Is Ready for Space Lasers,” NASA Mars Perseverance Rover, 28 September 2020, URL: https://www.nasa.gov/feature/jpl/nasas-new-mars-rover-is-ready-for-space-lasers
19) ”NASA's Ingenuity Mars Helicopter Recharges Its Batteries in Flight,” NASA/JPL, 13 August 2020, URL: https://www.jpl.nasa.gov/news/news.php?release=2020-157
20) ”A European dream team for Mars,” ESA Science & Exploration, 30 July 2020, URL: https://www.esa.int/Science_Exploration/
21) Mars 2020 mission instruments, NASA News, 31 July 2014, URL: https://mars.nasa.gov/mars2020/mission/instruments/
22) ”NASA Announces Mars 2020 Rover Payload to Explore the Red Planet as Never Before,” NASA News, 31 July 2014, URL: https://mars.nasa.gov/news/
23) ”Mars 2020,” NASA Fact Sheet, URL: https://mars.nasa.gov/mars2020/files/mars2020/Mars2020_Fact_Sheet.pdf
24) ”Mastcam-Z for Scientists,” NASA Mars 2020 mission, URL: https://mars.nasa.gov/mars2020/mission/instruments/mastcam-z/for-scientists/
25) ”SuperCam for Scientists,” NASA, URL: https://mars.nasa.gov/mars2020/mission/instruments/supercam/for-scientists/
26) ”All About the Laser (and Microphone) Atop Mars 2020, NASA's Next Rover,” NASA/JPL, 7 February 2020, URL: https://www.jpl.nasa.gov/news/news.php?release=2020-026
27) ”PIXL for Scientists,” NASA, URL: https://mars.nasa.gov
28) ”SHERLOC for Scientists,” NASA, URL: https://mars.nasa.gov
29) ”Johnson-Built Device to Help Mars 2020 Rover Search for Signs of Life,” NASA/JSC, 12 June 2019, URL: https://mars.nasa.gov/news/8448/
30) ”SHERLOC Calibration Target in the Clean Room,” NASA, 12 June 2019, URL: https://mars.nasa.gov/resources/22534/sherloc-calibration-target-in-the-clean-room/
31) ”MOXIE for Scientists,” NASA, URL: https://mars.nasa.gov
32) ”MEDA for Scientists,” NASA, URL: https://mars.nasa.gov
33) ”RIMFAX for Scientists,” NASA, Mars 2020 Mission, URL: https://mars.nasa.gov
34) ” Communications with Earth,” NASA, Mars 2020 Mission, URL: https://mars.nasa.gov/mars2020/mission/communications/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).