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 Mars Exploration[Rover misson]

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stormgrab
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PostSubject: Mars Exploration[Rover misson]   Tue Mar 10, 2009 3:39 pm

Mars Exploration Rover Mission
I INTRODUCTION

Mars Exploration Rover Mission, robotic exploration of Mars carried out by the National Aeronautics and Space Administration (NASA) of the United States beginning in 2003. The primary goal of the mission was to land two highly mobile vehicles known as rovers at separate landing sites on Mars so that they could search for evidence that liquid water once existed on the planet’s surface. Equipped with scientific instruments, the rovers landed at sites chosen because they were likely to provide information on whether liquid water once existed on Mars. Water is essential to life, and scientists believe that if water once existed on Mars, then life might have evolved there in the distant past. The mission was regarded as a major scientific and engineering success, resulting in important new discoveries about the so-called Red Planet, including the finding that large areas of Mars once had liquid water.

The rovers were designed, built, and tested from 2000 to 2003 by a large team led by the California Institute of Technology’s Jet Propulsion Laboratory (JPL) in Pasadena, California. JPL is managed by the California Institute of Technology for NASA. The rover team included scientists and engineers from NASA, professors at U.S. and European universities, and private contractors. More than 1,000 people around the world were directly involved in the rovers’ design, assembly, and software development work. Once the rovers landed on Mars, a worldwide team of several hundred people became involved in the rovers’ day-to-day operations.

Assembly, test, launch, and a year of operations of each rover cost about $425 million, or about the same amount of money as it cost to make the movies Titanic (1997) and Pearl Harbor (2001). This amount was also equivalent to what it costs to launch a single space-shuttle mission. The rovers are part of a new class of less expensive NASA spacecraft, with costs similar to other recent Mars orbiters and smaller missions such as the Lunar Prospector. These missions cost hundreds of millions of dollars compared with the Viking spacecraft of the 1970s, or the more recent Hubble Space Telescope or Cassini Saturn orbiter missions, which each cost several billion dollars.

The first rover, Spirit, was launched on a Delta rocket from Cape Canaveral, Florida, on June 10, 2003. Spirit was targeted to land inside Gusev Crater, a 160-km (100-mi) wide crater in the southern hemisphere of Mars. Images and other data from orbiting spacecraft such as Viking, Mars Global Surveyor (MGS), and Mars Odyssey showed an enormous meandering channel, possibly a dry riverbed, which ends in Gusev Crater. This finding suggested that Gusev may once have been a water-filled lake. One of Spirit's primary goals was to search for evidence of whether Gusev ever contained liquid water, and if so, for how long.

The second rover, Opportunity, also part of a larger spacecraft, was launched on a similar Delta rocket from Cape Canaveral, Florida, on July 7, 2003. Opportunity was targeted to a landing site halfway around the planet from Gusev, in a smooth region just south of the equator called Meridiani Planum. Meridiani is among the flattest places on Mars and thus was judged to be a safer rover landing site than Gusev. The decision to land in Meridiani was mostly based on scientific observations from the MGS orbiter, which had detected evidence for deposits of the coarse-grained mineral hematite (Fe2O3) in this part of the planet. Coarse-grained hematite often forms on Earth in the presence of substantial amounts of liquid water. Opportunity's primary goals were to confirm the presence of hematite in Meridiani, to determine if it was formed by liquid water, and if so, to provide clues about how much water was there and how long it lasted.

After a seven-month interplanetary cruise to Mars traveling at a speed of about 19,000 km/h (12,000 mph), the spacecraft that carried each rover went through a six-minute thrill ride to decelerate and land. Each spacecraft used a heat shield to protect it from the heat of atmospheric entry, a parachute to slow the craft, retro-rockets to bring the craft to a near-hovered stop just above the surface, and finally a set of inflated airbags to cushion the blow of impact and allow the spacecraft to bounce around to a gentle stop. The Spirit spacecraft landed successfully on January 4, 2004, and the Opportunity spacecraft landed successfully on January 24, 2004. Once operators on Earth determined that it was safe to begin the mission, each spacecraft unfolded and deployed its various instruments, and the rovers rolled out on a ramp onto the surface of the planet. Spirit rolled onto the surface on January 15, and Opportunity was deployed onto the surface on January 31.

The landing procedure was similar to that of the successful 1997 Mars Pathfinder mission. However, the two identical rovers differ significantly from the earlier Sojourner rover on the Pathfinder mission. The Mars Exploration rovers are larger and heavier. Whereas Sojourner was 65 cm (2 ft) long with a mass of 10 kg (22 lb on Earth; 8 lb on Mars), each of the Mars Exploration rovers is 1.6 m (5.2 ft) long and has a mass of 174 kg (384 lb on Earth; 144 lb on Mars). The six-wheeled Mars Exploration rovers also have a suspension system that enables them to ride over rocks bigger than 26 cm (10 in) and to tilt up to about 30 degrees without turning over.
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stormgrab
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PostSubject: Re: Mars Exploration[Rover misson]   Tue Mar 10, 2009 3:40 pm

II THE ROVERS’ INSTRUMENTS AND NAVIGATION

Each rover is outfitted with a suite of sophisticated scientific instruments that enable scientists to study in detail the geology and composition of materials at each landing site. Two of the instruments are mounted on the rover mast, about 1.5 m (5 ft) above the surface. One of these instruments is a high-resolution digital camera system called Pancam. The Pancam takes three-dimensional images of an area to reveal its topography and to calculate the distances to various targets of interest. It also takes color images in ultraviolet, visible, and near-infrared wavelengths for studies of Mars’s rocks, soils, and atmosphere. The other instrument is an infrared spectrometer called Mini-TES. A spectrometer is a scientific instrument that disperses the light emitted or reflected by a substance into a spectrum (individual colors). Because every substance has its own unique spectrum, scientists can use a spectrometer to identify the substance and study its chemical properties. Mini-TES was used to determine the mineral composition of rocks and soils around the rovers and to study the way the atmosphere heats up and cools down as a result of daily weather patterns or occasional dust storms.

Still more instruments are mounted on a flexible robotic arm used to study rocks and soils up close. These instruments include a camera called the Microscopic Imager with a magnifying power on the scale of a handheld magnifying lens and a grinding device called the Rock Abrasion Tool (RAT) used to clean off dusty rock surfaces. The RAT can also grind a few millimeters to a centimeter (up to about half an inch) into rocks to expose their interiors for detailed study. Two different types of spectrometers are also attached to the robotic arm—an Alpha Particle X-Ray spectrometer for determining the elemental composition of rocks and soils (such as the amount of iron, silicon, aluminum, sulfur, and other chemical elements) and a Mössbauer spectrometer for identifying iron-bearing minerals.

The rovers are also equipped with high-tech engineering systems for power, communications, temperature control, and onboard data processing. The rovers use solar panels to generate electricity during the daytime. This electricity is then used to drive and operate the instruments. Some of that power is also used to recharge a set of internal batteries that keep the rovers alive during the extremely cold Martian night when temperatures reach about -100°C (-150°F). These batteries also enable a limited number of nighttime scientific observations.

The rovers can communicate with Earth in three different ways. Two of the ways involve using direct-to-Earth high-gain or low-gain antenna radio systems to send data and receive instructions in 'real time,' or almost simultaneously. In this case, “real time” means about 10 minutes for data to be sent to Earth and another 10 minutes for instructions to be sent back to the rovers. A high-gain antenna has a narrow radiowave beam that can be directed at a specific target on Earth, while the low-gain antenna has a wider beam for a more reliable signal. The high-gain antenna can send more data to Earth than the low-gain antenna, but an even better way of transmitting data involves using an ultrahigh frequency (UHF) radio system. The UHF systems on the rovers send data to MGS or Mars Odyssey as they pass over the landing sites. Those satellites then relay the data to Earth. Because the UHF relay system can transmit much more data using significantly less power than the direct-to-Earth systems, the UHF system has been used to transmit more than 80 percent of the data from both rovers during the course of the mission.

The rovers are able to do much of their own driving. They had to be given significant onboard data processing and decision-making capabilities to do this driving. 'Real time,' or simultaneous, commanding or driving by JPL operators is not possible because it can take 20 minutes or more for radio signals to travel round trip from Earth to Mars. For driving, front- and rear-mounted Hazard Avoidance cameras and mast-mounted navigation cameras provide image data for onboard feature-detection and navigation software. For example, the cameras provide the images needed for the navigation software to instruct the rovers’ computers on how to approach rock targets, dig shallow trenches with its wheels, or traverse 100 m (328 ft) or more per sol, or Martian day. (A Martian day is about 40 minutes longer than an Earth day.)
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Arijit
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PostSubject: Re: Mars Exploration[Rover misson]   Tue Mar 10, 2009 3:40 pm

Thank you for sharing the information.
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stormgrab
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PostSubject: Re: Mars Exploration[Rover misson]   Wed Mar 11, 2009 8:03 pm

You are most welcome.
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