Curiosity on Mars

The Science Payload
Rock Zappers and the Search for Biosignatures
Written and edited by Bob Keller

Curiosity's Science Payload

Curiosity's science payload consists of its Sample Acquisition, Processing, and Handling subsystem and 10 scientific instruments. There are four categories of instruments:
Remote Sensing Instruments (2): Mast Camera (Mastcam) and Laser-Induced Breakdown Spectroscopy for Chemistry and Microimaging (ChemCam) located on the remote sensing mast
Contact Science Instruments (2): Alpha Particle X-ray Spectrometer (APXS) and Mars Hand Lens Imager (MAHLI) located on the end of the robotic arm
Analytical Laboratory Instruments (2): Chemistry and Mineralogy (CheMin) and Sample Analysis at Mars (SAM) located inside the rover body
Environmental Instruments (4): Radiation Assessment Detector (RAD), Dynamic Albedo of Neutrons (DAN), Rover Environmental Monitoring Station (REMS), and Mars Descent Imager (MARDI).

Sample Acquisition, Processing, and Handling (SA/SPaH) Subsystem

Curiosity's Sample Acquisition, Processing, and Handling Subsystem

Curiosity's Sample Acquisition, Processing, and Handling Subsystem The Sample Acquisition, Processing, and Handling (SA/SPaH) subsystem is responsible for the acquisition of rock and soil samples from the Martian surface and the processing of these samples into fine particles that are then distributed to the analytical science instruments, SAM and CheMin.

The SA/SPaH subsystem is also responsible for the placement of the two contact instruments, APXS and MAHLI, on rock and soil targets. SA/SPaH consists of a Robotic Arm and turret-mounted devices on the end of the arm, which include a drill, brush, soil scoop, sample processing device, and the mechanical and electrical interfaces to the two contact science instruments.

SA/SPaH also includes drill bit boxes, the Organic Check Material (OCM), and an observation tray, which are all mounted on the front of the rover, and inlet cover mechanisms that are placed over the SAM and CheMin solid sample inlet tubes on the rover top deck.

Curiosity's Robotic Arm is a 5 degree-of-freedom manipulator that is used to place and hold the turret-mounted devices and instruments on rock and soil targets, as well as manipulate the turret-mounted sample processing hardware. The 5 degrees of freedom are provided by a set of rotary actuators known as the shoulder azimuth joint, the shoulder elevation joint, the elbow joint, the wrist joint, and the turret joint.

The joints are connected by structural elements with long links connecting the shoulder and elbow joints (the upper arm link) and connecting the elbow and wrist joints (the forearm link). When fully extended straight ahead in the rover forward drive direction, the center of the turret of the robotic arm is 6 feet from the front of the rover body.

At the end of the Robotic Arm is the turret structure on which 5 devices are mounted. The outer diameter of the turret plus the installed devices is approximately 2 feet. Two of these devices are the science contact instruments APXS and MAHLI. The remaining three devices are associated with sample acquisition and sample preparation function: the Powder Acquisition Drill System (PADS), Dust Removal Tool (DRT), and the Collection and Handling for Interior Martian Rock Analysis (CHIMRA). The robotic arm can meet its positioning requirements for targets inside a volume called the robotic arm workspace. The workspace volume is an upright cylinder approximately 31 inches in diameter, 39 inches high, positioned 41 inches in front of the front body of the rover, and extending to 8 inches below the surface when the rover is on a smooth flat terrain.

One of Curiosity's Two Mast Cameras The Mast Camera (Mastcam)

The Mast Camera will take color images and color video footage of the Martian terrain. The images can be stitched together to create panoramas of the landscape around the rover. The Mastcam design consists of two camera systems mounted on a mast extending upward from the Curiosity rover's deck. The Mastcam will be used to study the Martian landscape, rocks, and soils; to view frost and weather phenomena; and to support the driving and sampling operations of the rover.

Several new features on the Mastcam distinguish it from previous rover cameras: One of the two Mastcam camera systems has a moderate-resolution lens, similar to the Pancam on the Mars Exploration Rovers. The other camera system has a high-resolution lens in order to study the landscape far from the rover. The Mastcam can take high-definition video at 10 frames per second.

The Mastcam is designed to take single-exposure, color snapshots similar to those taken with a consumer digital camera on Earth. In addition, it has multiple filters for taking sets of monochromatic (single-color) images. These images are used to analyze patterns of light absorption in different portions of the electromagnetic spectrum. Electronics on the Mastcam process images independently of the rover's central processing unit. The Mastcam has an internal data buffer for storing thousands of images or several hours of high-definition video footage for transmission to Earth.

Curiosity's Mars Hand Lens Imager Mars Hand Lens Imager (MAHLI)

Second only to the rock hammer, the hand lens is an essential tool of human geologists. Usually carried on a string around the neck, the hand lens helps a geologist in the field identify the minerals in a rock. The robotic geologist Curiosity will carry its own equivalent of the geologist's hand lens, the Mars Hand Lens Imager.

MAHLI will provide earthbound scientists with close-up views of the minerals, textures, and structures in Martian rocks and the surface layer of rocky debris and dust. The self-focusing, roughly 4-centimeter-wide (1.5-inch-wide) camera will take color images of features as small as 12.5 micrometers, smaller than the diameter of a human hair. MAHLI employs both white light sources, similar to the light from a flashlight, and ultraviolet light sources, similar to the light from a tanning lamp, making the imager functional both day and night. The ultraviolet light will be used to induce fluorescence to help detect carbonate and evaporite minerals, both of which indicate that water helped shape the landscape on Mars.

MAHLI's main objective is to help the Mars Science Laboratory science team understand the geologic history of the landing site on Mars and will also help researchers select samples for further investigation.

Curiosity's Alpha Particle X-Ray Spectrometer Alpha Particle X-Ray Spectrometer (APXS)

The Alpha Particle X-Ray Spectrometer will measure the abundance of chemical elements in rocks and soils. The APXS will be placed in contact with rock and soil samples on Mars and will expose the material to alpha particles and X-rays emitted during the radioactive decay of the element curium.

Alpha particles are helium nuclei, consisting of 2 protons and 2 neutrons. When X-rays and alpha particles interact with atoms in the surface material, they knock electrons out of their orbits, producing an energy release by emitting X-rays that can be measured with detectors. The X-ray energies enable scientists to identify all important rock-forming elements, from sodium to heavier elements.

The APXS will take measurements both day and night. Its sensor head is designed to be smaller than a soda can and will contain a highly sensitive X-ray detector in the middle of an array of curium sources. The longer the instrument is held in place on the surface of a rock or soil sample, the more clearly the signal from the sample can be determined. Most APXS measurements will take two to three hours to reveal all elements, including small amounts of trace elements. Ten minutes of operation will be sufficient for a quick look at major elements.

As a contact instrument, the APXS is designed to work in concert with other payload elements on the instrument arm and in the body of the Curiosity rover, such as the CheMin instrument and the Dust Removal Tool (brush). Scientists will use the APXS to help characterize and select rock and soil samples and then examine the interiors of the rocks following brushing. By analyzing the elemental composition of rocks and soils, scientists will seek to understand how the material formed and if it was later altered by wind, water, or ice. The APXS on NASA's two Mars Exploration Rovers has already provided evidence that water once played a major role in Mars' geologic past.

Laser-Induced Breakdown Spectroscopy for Chemistry and Microimaging (ChemCam)

Body and Mast Units of Curiosity's ChemCam Instrument

Looking at rocks and soils from a distance, ChemCam will fire a laser and analyze the elemental composition of vaporized materials from areas smaller than 1 millimeter on the surface of Martian rocks and soils. An on-board spectrograph will provide unprecedented detail about minerals and microstructures in rocks by measuring the composition of the resulting plasma -- an extremely hot gas made of free-floating ions and electrons.

ChemCam will also use the laser to clear away dust from Martian rocks and a remote camera to acquire extremely detailed images. The camera can resolve features 5 to 10 times smaller than those visible with cameras on the Spirit and Opportunity Rovers that began exploring the Red Planet in January 2004. In the event the Mars Science Laboratory rover can't reach a rock or outcrop of interest, ChemCam will have the capability to analyze it from a distance.

From up to 23 feet away, ChemCam will be able to: Rapidly identify the kind of rock being studied (for example, whether it is volcanic or sedimentary); Determine the composition of soils and pebbles; Measure the abundance of all chemical elements, including trace elements and those that might be hazardous to humans; Recognize ice and minerals with water molecules in their crystal structures; Measure the depth and composition of weathering rinds on rocks; and Provide visual assistance during drilling of rock cores.

The ChemCam instrument has two parts: a mast package and a body unit. On the mast will be a telescope to focus the laser and the camera, a laser for vaporizing surfaces, and a remote micro-imager. The mast package can be tilted or rotated as needed for optimum viewing of the rock. Light from the telescope will travel along a fiber-optic link to a body unit inside the rover. The body unit will carry three spectrographs for dividing the plasma light into its constituent wavelengths for chemical analysis. The body unit will also have its own power supply and an electronic interface to the rover's central computer system.

Chemistry and Mineralogy Instrument (CheMin)

The Chemistry and Mineralogy instrument will identify and measure the abundances of various minerals on Mars. Examples of minerals found on Mars so far are olivine, pyroxenes, hematite, goethite, and magnetite.

Minerals are indicative of environmental conditions that existed when they formed. For example, olivine and pyroxene, two primary minerals in basalt, form when lava solidifies. Jarosite, found in sedimentary rocks by NASA's Opportunity rover on Mars, precipitates out of water.

Using CheMin, scientists will be able to study further the role that water, an essential ingredient for life as we know it, played in forming minerals on Mars. For example, gypsum is a mineral that contains calcium, sulfur, and water. Anhydrite is a calcium and sulfur mineral with no water in its crystal structure. CheMin will be able to distinguish the two. Different minerals are linked to certain kinds of environments. Scientists will use CheMin to search for mineral clues indicative of a past Martian environment that might have supported life.

To prepare rock samples for analysis, the rover will be able to drill into rocks, collect the resulting fine powder, sieve it, and deliver it to a sample holder. It will use a scoop for collecting soil. CheMin will then direct a beam of X-rays as fine as a human hair through the powdered material. X-rays, like visible light, are a form of electromagnetic radiation. They have a much shorter wavelength that cannot be seen with the naked eye. When the X-ray beam interacts with the rock or soil sample, some of the X-rays will be absorbed by atoms in the sample and re-emitted or fluoresced at energies that are characteristic of the particular atoms present.

In X-ray diffraction, some X-rays bounce away at the same angle from the internal crystal structure in the sample. When this happens, they mutually reinforce each other and produce a distinctive signal. Scientists can measure the angle at which X-rays are diffracted toward the detector and use that to identify minerals. For example, if the mineral halite (common table salt, or NaCl), were placed in CheMin, the instrument would produce a specific diffraction pattern that would identify the structure of halite.

Because all minerals diffract X-rays in a characteristic pattern and all elements emit X-rays with a unique set of energy levels, scientists will use the information from X-ray diffraction to identify the crystalline structure of materials the rover encounters on Mars. A Charge-Coupled Device (CCD) will collect both diffraction and fluorescence information.

Sample Analysis at Mars Instrument Suite (SAM)

Curiosity's Sample Analysis at Mars Instrument Suite

The Sample Analysis at Mars instrument suite takes up more than half the science payload on board the Curiosity rover and features chemical equipment found in many scientific laboratories on Earth. Sample Analysis at Mars will search for compounds of the element carbon, including methane, that are associated with life and explore ways in which they are generated and destroyed in the Martian ecosphere.

Actually a suite of three instruments, including a mass spectrometer, gas chromatograph, and tunable laser spectrometer, Sample Analysis at Mars will also look for and measure the abundances of other light elements, such as hydrogen, oxygen, and nitrogen, that are associated with life.

The mass spectrometer will separate elements and compounds by mass for identification and measurement. The gas chromatograph will heat soil and rock samples until they vaporize, and will then separate the resulting gases into various components for analysis. The laser spectrometer will measure the abundance of various isotopes of carbon, hydrogen, and oxygen in atmospheric gases such as methane, water vapor, and carbon dioxide. These measurements will be accurate to within 10 parts per thousand.

Because these compounds are essential to life as we know it, their relative abundances will be an essential piece of information for evaluating whether Mars could have supported life in the past or present.

Curiosity's Radiation Assessment Detector Radiation Assessment Detector (RAD)

The Radiation Assessment Detector is one of the first instruments sent to Mars specifically to prepare for future human exploration. The size of a small toaster or six-pack of soda, RAD will measure and identify all high-energy radiation on the Martian surface, such as protons, energetic ions of various elements, neutrons, and gamma rays. That includes not only direct radiation from space, but also secondary radiation produced by the interaction of space radiation with the Martian atmosphere and surface rocks and soils.

To prepare for future human exploration, RAD will collect data that will allow scientists to calculate the equivalent dose (a measure of the effect radiation has on humans) to which people would be exposed on the surface of Mars. RAD will also assess the hazard presented by radiation to potential microbial life, past and present, both on and beneath the Martian surface. In addition, RAD will investigate how radiation has affected the chemical and isotopic composition of Martian rocks and soils.

A stack of paper-thin, silicon detectors and a small block of cesium iodide measure high-energy charged particles coming through the Martian atmosphere. As the particles pass through the detectors, they lose energy, producing electron or light pulses. An internal signal processor analyzes the pulses to identify each high-energy particle and determine its energy.

In addition to identifying neutrons, gamma rays, protons, and alpha particles, RAD will identify heavy ions up to iron on the periodic table. The RAD will be lightweight and energy efficient so as to use as little of the Mars Science Laboratory's available mass and energy resources as possible.

Dynamic Albedo of Neutrons (DAN)

One way to look for water on Mars is to look for neutrons escaping from the planet's surface. Cosmic rays from space constantly bombard the surface of Mars, knocking neutrons in soils and rocks out of their atomic orbits. If liquid or frozen water happens to be present, hydrogen atoms slow the neutrons down. In this way, some of the neutrons escaping into space have less energy and move more slowly. These slower particles can be measured with a neutron detector.

Scientists expect to find hydrogen on Mars in two forms: water ice and minerals that have molecules of water in their crystal structures. The Curiosity rover will carry a pulsing neutron generator called the Dynamic Albedo of Neutrons that will be sensitive enough to detect water content as low as one-tenth of 1 percent and resolve layers of water and ice beneath the surface. Albedo is a scientific word for the reflection or scattering of light. DAN will focus a beam of neutrons on the Martian surface from a height of 2.6 feet. The neutrons are expected to travel 3 to 6 feet below the surface before being absorbed by hydrogen atoms in subsurface ice.

Scientists estimate that, near the Martian poles, water ice makes up 30 percent to 50 percent of shallow subsurface deposits. If the beam of neutrons encounters a layer of water ice beneath the surface, DAN will detect a relatively greater number of slower neutrons reflected at the surface. If there are no ice layers or water-logged minerals beneath the surface, DAN will detect a relatively greater amount of faster neutrons reflected at the surface.>/p>

Rover Environmental Monitoring Station (REMS)

The Rover Environmental Monitoring Station will measure and provide daily and seasonal reports on atmospheric pressure, humidity, ultraviolet radiation at the Martian surface, wind speed and direction, air temperature, and ground temperature around the rover.

Two small booms on the rover mast will record the horizontal and vertical components of wind speed to characterize air flow near the Martian surface from breezes, dust devils, and dust storms. A sensor inside the rover's electronic box will be exposed to the atmosphere through a small opening and will measure changes in pressure caused by different meteorological events such as dust devils, atmospheric tides, and cold and warm fronts. A small filter will shield the sensor against dust contamination.

A suite of infrared sensors on one of the booms will measure the intensity of infrared radiation emitted by the ground, which will provide an estimate of ground temperature. These data will provide the basis for computing ground temperature. A sensor on the other boom will track atmospheric humidity. Both booms will carry sensors for measuring air temperature.

An array of detectors on the rover deck that are sensitive to specific frequencies of sunlight will measure ultraviolet radiation at the Martian surface and correlate it with changes in the other environmental variables.

Mars Descent Imager

Mars Descent Imager (MARDI)

Knowing the location of loose debris, boulders, cliffs, and other features of the terrain will be vital for planning the path of exploration after the Curiosity rover arrives on the Red Planet. The Mars Descent Imager has acquired color video during the rover's descent toward the surface, providing an "astronaut's view" of the local environment.

Upon jettisoning its heat shield several kilometers above the Martian surface, the Mars Descent Imager commenced producing a five-frames-per-second video stream of high-resolution, overhead views of the landing site. It continued acquiring images until the rover touched down, storing the video data in digital memory. After landing safely on Mars, the rover is programmed to transfer the data to Earth.

In addition to helping Earthbound mission planners select an optimum path of exploration, the Mars Descent Imager will provide information about the larger geologic context surrounding the landing site. It will also enable mappers to determine the spacecraft's precise location after landing.

Mars Science Laboratory Entry, Descent, and Landing Instrument Suite (MEDLI)

MEDLI collected engineering data during the spacecraft's high-speed, extremely hot entry into the Martian atmosphere. MEDLI data will be invaluable to engineers when they design future Mars missions. The data will help them design systems for entry into the Martian atmosphere that are safer, more reliable, and lighter weight. MEDLI is actually made up of two kinds of instruments (with seven sensors of each kind) that are installed in 14 places on the spacecraft's heat shield. The two kinds of instruments are:

MEDLI Integrated Sensor Plug MEDLI Integrated Sensor Plugs (MISP) When the spacecraft faced extreme heat during entry into the Martian atmosphere, MISP measured how hot it gets at different depths in the spacecraft's heat-shield material. Predicted heating levels are about three times higher than those of the Space Shuttle when it enters Earth's atmosphere. The heating levels are so high, in fact, that the spacecraft's thermal protection system is designed to burn away during entry into Mars' atmosphere.

MISP will measure the rate of this burning, also known as "recession." When they designed the heat shield, engineers predicted what they thought the heating rate would be as a function of time. They will compare their predictions to the actual data collected by MISP. That information will help them learn how much heat-shield material will be needed to protect future Mars missions.

Mars Entry Atmospheric Data System (MEADS) MEADS measured the atmospheric pressure on the heat shield at the seven MEADS locations during entry and descent through Mars' atmosphere. The MEADS pressure sensors are arranged in a special cross pattern. This cross pattern will allow engineers to determine the spacecraft's orientation (its position and how that changes) as a function of time. Engineers will use this information to see how well their models predicted the spacecraft's real trajectory and its aerodynamics. That information will allow them to plan future missions that will have even better performance during critical stages of entry, descent, and landing.


Table of Contents

Bob Keller