Curiosity Rover

The Curiosity rover is a nuclear-powered exploration vehicle that is part of NASA’s Mars Science Laboratory (MSL) mission. The MSL spacecraft was launched in late 2011 and successfully landed on Aeolis Palus in Gale Crater in the summer of 2012. The approximately 2 billion-year-old impact crater is hypothesized to have gradually been filled in, first by water-deposited, and then by wind-deposited sediments, possibly until it was completely covered, before wind erosion scoured out the sediments, leaving an isolated 5.5 km (3.4 mile) high mountain, Aeolis Mons, at the center of the 154 km (96 mi) wide crater.

Thus, it is believed that the rover may have the opportunity to study two billion years of Martian history in the sediments exposed in the mountain. Additionally, its landing site should be on or near an alluvial fan, which is hypothesized to be the result of a flow of ground water, either before the deposition of the eroded sediments or else in relatively recent geologic history.

The MSL mission has four scientific goals: 1) Determine whether Mars could ever have supported life; 2) Study the climate of Mars; 3) Study the geology of Mars; and 4) Plan for a human mission to Mars. The Curiosity rover is 3 m (9.8 ft) in length, and weighs 900 kg (2,000 lb), including 80 kg (180 lb) of scientific instruments (about the size of a small SUV). Curiosity will be able to roll over obstacles approaching 75 cm (30 in) in height. Maximum terrain-traverse speed is estimated to be 90 m (300 ft) per hour by automatic navigation; average traverse speeds will likely be about 30 m (98 ft) per hour, based on variables including power levels, terrain difficulty, slippage, and visibility. The rover is expected to traverse a minimum of 19 km (12 mi) in its two-year mission.

Curiosity is powered by a radioisotope thermoelectric generator (RTG), like the successful Viking 1 and Viking 2 Mars landers in 1976. Radioisotope power systems (RPSs) are generators that produce electricity from the natural decay of plutonium-238, which is a non-fissile isotope. Heat given off by natural decay is converted into electricity, providing constant power during all seasons and through the day and night, and waste heat can be used via pipes to warm systems, freeing electrical power for the operation of the vehicle and instruments. Curiosity’s RTG is fueled by 4.8 kg (11 lb) of plutonium-238 dioxide supplied by the U.S. Department of Energy, packed in 32 pellets each about the size of a marshmallow.

Curiosity’s power generator is the latest RTG generation built by Boeing, called the ‘Multi-Mission Radioisotope Thermoelectric Generator’ or MMRTG. Based on classical RTG technology, it represents a more flexible and compact development step, and is designed to produce 125 watts of electrical power from about 2000 watts of thermal power at the start of the mission. The MMRTG produces less power over time as its plutonium fuel decays: at its minimum lifetime of 14 years, electrical power output is down to 100 watts. The power source will generate 2.5 kilowatt hours per day, much more than the Mars Exploration Rovers’ solar panels, which can generate about 0.6 kilowatt hours per day.

The temperatures the rover operates in can vary from +30 to −127 °C (+86 °F to −197 °F). Therefore, the heat rejection system (HRS) uses fluid pumped through 60 m (200 ft) of tubing in the rover body so that sensitive components are kept at optimal temperatures. Other methods of heating the internal components include using radiated heat generated from the components in the craft itself, as well as excess heat from the MMRTG unit. The HRS also has the ability to cool components if necessary.

The two identical on-board rover computers, called ‘Rover Compute Element’ (RCE), contain radiation hardened memory to tolerate the extreme radiation from space and to safeguard against power-off cycles. Each computer’s memory includes 256 kB of EEPROM, 256 MB of DRAM, and 2 GB of flash memory. This compares to 3 MB of EEPROM, 128 MB of DRAM, and 256 MB of flash memory used in the Mars Exploration Rovers. The RCE computers use the RAD750 CPU, which is a successor to the RAD6000 CPU used in the Mars Exploration Rovers. The RAD750 CPU is capable of up to 400 MIPS, while the RAD6000 CPU is capable of up to 35 MIPS (an iPhone 4S is rated at 5,000 MIPS). Of the two on-board computers, one is configured as backup, and will take over in the event of problems with the main computer. The rover has an Inertial Measurement Unit (IMU) that provides 3-axis information on its position, which is used in rover navigation. The rover’s computers are constantly self-monitoring to keep the rover operational, such as by regulating the rover’s temperature. Activities such as taking pictures, driving, and operating the instruments are performed in a command sequence that is sent from the flight team to the rover.

Like previous rovers Mars Exploration Rovers and Mars Pathfinder, Curiosity is equipped with 6 wheels in a rocker-bogie suspension. The suspension system also served as landing gear for the vehicle, unlike its smaller predecessors. Curiosity’s wheels with a diameter of 20 in (51 cm) are significantly larger than those used on previous rovers. Each wheel has a tread pattern that helps it maintain traction, but also leaves patterned tracks in the sandy surface of Mars. On-board cameras use that pattern to estimate the distance traveled. The pattern itself includes a representation of the Morse code for ‘JPL’ (Jet Propulsion Laboratory).

Previous NASA Mars rovers only became active after the successful entry, descent and landing on the Martian surface. Curiosity, on the other hand, utilized the rover suspension system for the final set-down of the active rover on the surface of Mars. Curiosity transformed from its stowed flight configuration to a landing configuration while the MSL spacecraft simultaneously lowered it beneath the spacecraft descent stage with a 65 foot (20 m) tether from the ‘sky crane’ system to a soft landing—wheels down—on the surface of Mars. After the rover touched down it waited 2 seconds to confirm that it was on solid ground and fired several pyros (small explosive devices) activating cable cutters on the bridle to free itself from the spacecraft descent stage. The descent stage then flew away to a crash landing, and the rover prepared itself to begin the science portion of the mission.

Curiosity has two means of communication – an X band (8.0–12.0 GHz) transmitter and receiver that can communicate directly with Earth, and a UHF Electra-Lite software-defined radio (SDR) for communicating with Mars orbiters. The SDR is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software. Communication with orbiters is expected to be the main path for data return to Earth, since the orbiters have both more power and larger antennas than the lander. An average of 14 minutes, 6 seconds will be required for signals to travel between Earth and Mars.

The general analysis strategy begins with high resolution cameras to look for features of interest. If a particular surface is of interest, Curiosity can vaporize a small portion of it with an infrared laser and examine the resulting spectra signature to query the rock’s elemental composition. If that signature intrigues, the rover will use its long arm to swing over a microscope and an X-ray spectrometer to take a closer look. If the specimen warrants further analysis, Curiosity can drill into the boulder and deliver a powdered sample to the analytical laboratory (SAM) inside the rover. The highly sensitive SAM analyzer has a limit of 74 sample cups.

The MastCam, MAHLI, and MARDI cameras were developed by Malin Space Science Systems. The MastCam system provides multiple spectra and true color imaging with two cameras. The cameras can take true color images at 1600×1200 pixels and up to 10 frames per second hardware-compressed, high-definition video at 720p (1280×720). One camera is the Medium Angle Camera (MAC), which has a 34 mm focal length, a 15-degree field of view, and can yield 22 cm/pixel scale at 1 km. The other camera is the Narrow Angle Camera (NAC), which has a 100 mm focal length, a 5.1-degree field of view, and can yield 7.4 cm/pixel scale at 1 km. Each camera has 8 GB of flash memory, which is capable of storing over 5,500 raw images, and can apply real time lossless or JPEG compression. The cameras have an autofocus capability that allows them to focus on objects from 2.1 m (6 ft 11 in) to infinity. Each camera also has a RGB Bayer pattern filter with 8 filter positions. In comparison to the 1024×1024 black and white panoramic cameras used on the Mars Exploration Rover (MER), the MAC MastCam has 1.25× higher spatial resolution and the NAC MastCam has 3.67× higher spatial resolution.

MAHLI consists of a camera mounted to a robotic arm on the rover, used to acquire microscopic images of rock and soil. MAHLI can take true color images at 1600×1200 pixels with a resolution as high as 14.5 micrometers per pixel. MAHLI has a 18.3 mm to 21.3 mm focal length and a 33.8- to 38.5-degree field of view. MAHLI has both white and ultraviolet LED illumination for imaging in darkness or fluorescence imaging. MAHLI also has mechanical focusing in a range from infinite to millimeter distances. This system can make some images with focus stacking (a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field than any of the individual source images). MAHLI can store either the raw images or do real time lossless predictive or JPEG compression.

During the descent to the Martian surface, MARDI will take color images at 1600×1200 pixels with a 1.3-millisecond exposure time starting at distances of about 3.7 km to near 5 meters from the ground and will take images at a rate of 5 frames per second for about 2 minutes. MARDI has a pixel scale of 1.5 meters at 2 km to 1.5 millimeters at 2 meters and has a 90-degree circular field of view. MARDI has 8 GB of internal buffer memory that is capable of storing over 4,000 raw images. MARDI imaging will allow the mapping of surrounding terrain and the location of landing. JunoCam (a visible-light camera/telescope for the Juno Jupiter Orbiter) is based on MARDI.

The rover has two pairs of black and white cameras (Hazcams) located on the four corners of the rover. They are used for autonomous hazard avoidance during rover drives and for safe positioning of the robotic arm on rocks and soils. The cameras use visible light to capture stereoscopic 3D imagery. The cameras have a 120 degree field of view and map the terrain at up to 3 m (9.8 ft) in front of the rover. This imagery safeguards against the rover crashing into unexpected obstacles, and works in tandem with software that allows the rover to make its own safety choices. The rover uses another pair of black and white cameras (Navcams) mounted on the mast to support ground navigation. The cameras have a 45 degree angle of view and use visible light to capture stereoscopic 3D imagery.

ChemCam is a suite of remote sensing instruments, including the first laser-induced breakdown spectroscopy (LIBS) system to be used for planetary science and a remote micro-imager (RMI). The LIBS instrument can target a rock or soil sample from up to 7 meters away, vaporizing a small amount of it with a 5-nanosecond pulse from a 1067 nm infrared laser and then collecting a spectrum of the light emitted by the vaporized rock. Detection of the ball of luminous plasma will be done in the visible and near-UV and near-IR range, between 240 nm and 800 nm. Using the same collection optics, the RMI provides context images of the LIBS analysis spots. The RMI resolves 1 mm objects at 10 m distance, and has a field of view covering 20 cm at that distance. The ChemCam instrument suite was developed by the Los Alamos National Laboratory and the French CESR laboratory.

The Rover Environmental Monitoring Station (REMS) comprises instruments to measure the Mars environment: humidity, pressure, temperatures, wind speeds, and ultra violet radiation. The meteorological package and an ultraviolet sensor were provided by the Spanish Ministry of Education and Science. The investigative team is led by Javier Gómez-Elvira of the Center for Astrobiology (Madrid) and includes the Finnish Meteorological Institute as a partner. All REMS 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. REMS will provide new clues about signature of the Martian general circulation, microscale weather systems, local hydrological cycle, destructive potential of UV radiation, and subsurface habitability based on ground-atmosphere interaction.

The APXS device irradiates samples with alpha particles and maps the spectra of X-rays that are re-emitted for determining the elemental composition of samples. The APXS is a form of particle-induced X-ray emission (PIXE), which has previously been used by the Mars Pathfinder and the Mars Exploration Rovers. The APXS was developed by the Canadian Space Agency. MacDonald Dettwiler (MDA), the Canadian aerospace company that built the Canadarm and RADARSAT (a pair of Canadian Remote Sensing satellites), were responsible for the engineering design and building of the APXS.

CheMin is the Chemistry and Mineralogy X-ray diffraction and X-ray fluorescence instrument. CheMin is one of four spectrometers. It will identify and quantify the abundance of the minerals on Mars. It was developed by David Blake at NASA Ames Research Center and the JPL. The rover will drill samples into rocks and the resulting fine powder will be sampled by the instrument. A beam of X-rays is then directed at the powder and the internal crystal structure of the minerals deflects back a pattern of X-rays. All minerals diffract X-rays in a characteristic pattern that allows scientists to identify the structure of the minerals the rover will encounter.

The Radiation assessment detector (RAD) was the first of ten MSL instruments to be turned on. On the route to Mars and while working on its surface, it will characterize the broad spectrum of radiation environment found inside the spacecraft. These measurements were never done before from the inside of a spacecraft and their main purpose is to determine the viability and shielding needs for human explorers. Funded by the Exploration Systems Mission Directorate at NASA Headquarters and Germany’s Space Agency (DLR), RAD was developed by Southwest Research Institute (SwRI) and the extraterrestrial physics group at Christian-Albrechts-Universität zu Kiel, Germany.

The Dynamic Albedo of Neutrons (DAN) device is a pulsed neutron source and detector for measuring hydrogen or ice and water at or near the Martian surface, provided by the Russian Federal Space Agency, and funded by Russia. The SAM (Sample Analysis at Mars) instrument suite will analyze organics and gases from both atmospheric and solid samples.

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