The Technology of Curiosity
- Saturday, 01 September 2012
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.