On April 14, 2004, NASA announced an opportunity for researchers to propose science investigations for the Mars Science Laboratory (MSL) mission. Eight months later, the agency announced selection of eight investigations. In addition, Spain and Russia would each provide an investigation through international agreements. The instruments for these ten investigations make up the science payload on the Curiosity rover.
The ten instruments on Curiosity have a combined mass of 165 pounds. Curiosity carries the instruments plus multiple systems that enable the science payload to do its job and send home the results. Key systems include six-wheeled mobility, sample acquisition and handling with a robotic arm, navigation using stereo imaging, a radioisotope power source, avionics, software, telecommunications, and thermal control.
Curiosity is 10 feet long (not counting its arm), 9 feet wide, and 7 feet high at the top of its mast, with a mass of 1,982 pounds, including the science instruments. Curiosity’s mechanical structure provides the basis for integrating all of the other rover subsystems and payload instruments.
Curiosity’s mobility subsystem is a scaled-up version of what was used on the three earlier Mars rovers: Sojourner, Spirit, and Opportunity. Six wheels all have driver motors, and the four corner wheels all have steering motors. Each front and rear wheel can be independently steered, allowing the vehicle to turn in place, as well as to drive in arcs. The suspension is a rocker-bogie system, enabling Curiosity to keep all its wheels in contact with the ground, even on uneven terrain. Curiosity’s wheels are aluminum and 20" in diameter. They have cleats for traction and structural support. Curving titanium spokes give springy support.
The rover has a top speed on flat, hard ground of about 1.5 inches per second. However, under autonomous control with hazard avoidance, the vehicle achieves an average speed of less than half that.
Arm and Turret
The Robot Arm (RA) is a five-degrees-of-freedom manipulator 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 science instruments on the arm’s turret are the Mars Hand Lens Imager (MAHLI) and the Alpha Particle X-ray Spectrometer (APXS). The other tools on the turret are components of the rover’s Sample Acquisition/Sample Processing and Handling (SA/SPaH) subsystem: the Powder Acquisition Drill System (PADS), the Dust Removal Tool (DRT), and the Collection and Handling for In-situ Martian Rock Analysis (CHIMRA) device.
The 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 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.
The Powder Acquisition Drill System is a rotary percussive drill to acquire samples of rock material for analysis. It can collect a sample from up to 2" beneath a rock’s surface. The drill penetrates the rock and powders the sample to the appropriate grain size for use in SAM and CheMin. If the drill bit becomes stuck in a rock, the drill can disengage from that bit and replace it with a spare. The Dust Removal Tool is a metal-bristle brushing device used to remove the dust layer from a rock surface or to clean the rover’s observation tray.
A clamshell-shaped scoop collects soil samples from the Martian surface. The other turret-mounted portion of this device has chambers used for sorting, sieving, and portioning the samples collected by the drill and the scoop. An observation tray on the rover allows the MAHLI and the APXS a place to examine collected and processed samples of soil and powdered rock.
Rover power is provided by a multi-mission radioisotope thermoelectric generator (MMRTG) supplied by the U.S. Department of Energy. This generator is essentially a nuclear battery that reliably converts heat into electricity. It consists of two major elements: a heat source that contains plutonium-238 dioxide, and a set of solid-state thermocouples that convert the plutonium’s heat energy to electricity. It contains 10.6 pounds of plutonium dioxide as the source of the steady supply of heat used to produce the onboard electricity, and to warm the rover’s systems during the Martian nights.
Curiosity has redundant main computers, or rover compute elements. Of this “A” and “B” pair, it uses one at a time, with the spare held in cold backup. So, at a given time, the rover is operating from either its A side or its B side. Each computer contains a radiation-hardened central processor with PowerPC 750 architecture, a BAE RAD 750 processor operating at up to 200 MHz speed. Each of Curiosity’s redundant computers has 2 gigabytes of flash memory, 256 megabytes of DRAM, and 256 kilobytes of EEPROM. The MSL flight software monitors the status and health of the spacecraft during all phases of the mission, checks for the presence of commands to execute, performs communication functions, and controls spacecraft activities.
Two sets of engineering cameras on the rover — Navigation cameras (Navcams) up high, and Hazard-avoidance cameras (Hazcams) down low — inform operational decisions both by Curiosity’s onboard autonomy software and by the rover team on Earth. Information from these cameras is used for autonomous navigation, engineers’ calculations for maneuvering the robotic arm, and scientists’ decisions about pointing the remote-sensing science instruments.
Each of the Navcams captures a square field of view 45 degrees wide and tall, comparable to the field of view of a 37-millimeter-focal-length lens on a 35- millimeter, single-lens-reflex camera. Curiosity has four pairs of Hazcams: two redundant pairs on the front of the chassis, and two at the rear. The rover can drive backwards as well as forward, so both the front and rear Hazcams can be used for detecting potential obstacles in the rover’s driving direction. The Hazcams have one-time-removable lens covers to shield them from potential dust raised during the rover’s landing.
Mast Camera (Mastcam)
Two two-megapixel color cameras on Curiosity’s mast are the left and right eyes of the Mastcam. These cameras have complementary capabilities for showing the rover’s surroundings in exquisite detail and in motion. The right-eye Mastcam looks through a telephoto lens with about three-fold better resolution than any previous landscape-viewing camera on the surface of Mars. The left-eye Mastcam provides broader context through a medium-angle lens. Each can acquire and store thousands of full-color images. Each is also capable of recording high-definition video.
The telephoto Mastcam is called Mastcam 100 for its 100-millimeter focal-length lens. The camera provides enough resolution to distinguish a basketball from a football at a distance of seven football fields. Its left-eye partner, called Mastcam 34 for its 34-millimeter lens, catches a scene three times wider on an identical detector.
Chemistry and Camera (ChemCam)
The ChemCam instrument consists of two remote sensing instruments: the first planetary science Laser-Induced Breakdown Spectrometer (LIBS), and a Remote Micro-Imager (RMI). The LIBS provides elemental compositions, while the RMI places the LIBS analyses in their geomorphologic context.
ChemCam uses a rock-zapping laser and a telescope mounted atop Curiosity’s mast. It also includes spectrometers and electronics inside the rover. The laser can hit rock or soil targets up to about 23 feet away with enough energy to excite a pinhead-size spot into a glowing, ionized gas called plasma. The instrument observes that spark with the telescope and analyzes the spectrum of light to identify the chemical elements in the target. The telescope doubles as the optics for the camera of ChemCam, which records monochrome images. The telescopic camera, called the remote micro-imager, will show context of the spots hit with the laser. It can also be used independently of the laser for observations of targets at any distance.
The spot hit by ChemCam’s infrared laser gets more than a million watts of power focused on it for five one-billionths of a second. Light from the resulting flash comes back to ChemCam through the telescope, then through about 20 feet of optical fiber down the mast to three spectrometers inside the rover. The spectrometers record intensity at 6,144 different wavelengths of ultraviolet, visible, and infrared light.
Alpha Particle X-Ray Spectrometer (APXS)
The APXS on Curiosity’s robotic arm will identify chemical elements in rocks and soils. A pinch of radioactive material emits radiation that “queries” the target and an X-ray detector “reads” the answer. The instrument consists of a main electronics unit in the rover’s body and a sensor head mounted on the robotic arm. Measurements are taken by deploying the sensor head towards a desired sample, placing the sensor head in contact or hovering, and measuring the emitted X-ray spectrum for 15 minutes to 3 hours without the need of further interaction by the rover.
Mars Hand Lens Imager (MAHLI)
MAHLI is a focusable color camera on Curiosity’s turret. Researchers will use it for magnified, close-up views of rocks and soils, and also for wider scenes of the ground, the landscape, or even the rover. Essentially, it is a handheld camera with a macro lens and autofocus.
The investigation takes its name from the type of hand lens magnifying tool that every field geologist carries for seeing details in rocks. MAHLI has two sets of white light-emitting diodes to enable imaging at night or in deep shadow. Two other LEDs on the instrument glow at the ultraviolet wavelength of 365 nanometers. These will make it possible to check for materials that fluoresce under this illumination.
This camera uses a red-green-blue filter grid like the one on commercial digital cameras for obtaining a full-color image with a single exposure. It stores images in an 8-Gb flash memory, and it can perform an onboard focus merge of eight images to reduce from eight to two the number of images returned to Earth in downlink-limited situations.
Chemistry and Mineralogy (CheMin)
CheMin is one of two investigations that will analyze powdered rock and soil samples delivered by Curiosity’s robotic arm. It will identify and quantify the minerals in the samples. CheMin uses X-ray diffraction, a first for a mission to Mars. It supplements the diffraction measurements with X-ray fluorescence capability to determine further details of composition by identifying ratios of specific elements present. X-ray diffraction works by directing an X-ray beam at a sample and recording how X-rays are scattered by the sample at the atomic level.
A sample processing tool on the robotic arm puts the powdered rock or soil through a sieve designed to remove any particles larger than 0.006” before delivering the material into the CheMin inlet funnel. Each sample analysis will use about as much material as in a baby aspirin.
Sample Analysis at Mars (SAM)
SAM is designed to explore molecular and elemental chemistry relevant to life. SAM addresses carbon chemistry through a search for organic compounds, the chemical state of light elements other than carbon, and isotopic tracers of planetary change. SAM is a suite of three instruments: a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC), and a Tunable Laser Spectrometer (TLS). The QMS and the GC can operate together in a GCMS mode for separation (GC) and definitive identification (QMS) of organic compounds.
SAM’s analytical tools fit into a microwave-oven-size box inside the front of the rover. While it is the biggest of the ten instruments on Curiosity, this tightly packed box holds instrumentation that would take up a good portion of a laboratory on Earth.
SAM’s sample manipulation system maneuvers 74 sample cups, each about one-sixth of a teaspoon in volume. The chemical separation and processing laboratory includes pumps, tubing, carrier- gas reservoirs, pressure monitors, ovens, temperature monitors, and other components.
Rover Environmental Monitoring Station (REMS)
REMS records six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and ultraviolet radiation. All sensors are located around three elements: two booms attached to the rover Remote Sensing Mast (RSM), the Ultraviolet Sensor (UVS) assembly located on the rover top deck, and the Instrument Control Unit (ICU) inside the rover body.
Radiation Assessment Detector (RAD)
RAD will monitor high-energy atomic and subatomic particles reaching Mars from the Sun, distant supernovas, and other sources. These particles constitute naturally occurring radiation that could be harmful to any microbes near the surface of Mars or to astronauts on a future Mars mission. RAD is an energetic particle analyzer designed to characterize the full spectrum of energetic particle radiation at the surface of Mars. RAD’s measurements will help fulfill MSL’s key goals of assessing whether Curiosity’s landing region has had conditions favorable for life and for preserving evidence about life.
Dynamic Albedo of Neutrons (DAN)
DAN is an active/passive neutron spectrometer that measures the abundance and depth distribution of H- and OHbearing materials in a shallow layer of Mars’ subsurface along the path of the rover. DAN can detect water bound into shallow underground minerals along Curiosity’s path. It shoots neutrons into the ground and measures how they are scattered, giving it a high sensitivity for finding any hydrogen to a depth of about 20" directly beneath the rover.
Mars Descent Imager (MARDI)
During the final few minutes of Curiosity’s flight to the surface of Mars, the Mars Descent Imager (MARDI) recorded a full-color video of the ground below. MARDI is a fixed-focus color camera mounted to the fore port side of the rover, even with the bottom of the rover chassis. The camera took images at 5 frames per second throughout the period of time between heat shield separation and touchdown. Throughout Curiosity’s mission on Mars, MARDI will offer the capability to obtain images of ground beneath the rover for tracking of its movements or for geologic mapping.
Learn more about Curiosity’s science instruments at http://mars.jpl.nasa.gov/msl/mission/science. View the latest videos of the Mars Science Laboratory and Curiosity rover on Tech Briefs TV at www.techbriefs.com/tv/mars. Get the latest news on the MSL mission at www.nasa.gov/mission_pages/msl/ .