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Mars Climate Orbiter Mars Climate Orbiter, United States spacecraft launched in 1998 to explore the planet Mars.

Publié le 11/05/2013

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Mars Climate Orbiter Mars Climate Orbiter, United States spacecraft launched in 1998 to explore the planet Mars. A navigational error caused the spacecraft to orbit too close to Mars, where it was apparently destroyed by friction with the Martian atmosphere. Mars Climate Orbiter was one of a series of U.S. Mars probes that began with Mars Global Surveyor 96 and Mars Pathfinder, a pair of spacecraft launched in 1996 and 1997. The probe was part of the Mars exploration strategy of the U.S. National Aeronautics and Space Administration (NASA). NASA's exploration of Mars focuses on learning about climate and on finding signs of life and useful resources. Mars Climate Orbiter was designed to provide a global view of the climate of Mars from an altitude of 400 km (250 mi) for an entire 687-day Martian year. It was to study clouds, dust storms, hazes, water vapor, and ozone in the Martian atmosphere. Mars Climate Orbiter was also designed to relay radio signals between Earth and Mars Polar Lander, a probe launched in 1999 that was to land on the Martian surface. NASA launched Mars Climate Orbiter toward Mars on December 11, 1998. The spacecraft had two main parts: a propulsion module and an equipment module. The propulsion module contained the main engine, four large thruster rockets, four small thrusters, and propellant tanks. The equipment module contained scientific instruments, batteries, computers, low-gain and medium-gain radio antennas, radio equipment, guidance systems, and reaction wheels for turning the spacecraft. A large solar array was attached to the orbiter and unfolded during flight. The array provided power to the craft and its systems. The orbiter also included an attached, high-gain dish antenna that was to provide a radio link to Earth once the craft was in orbit around Mars. Mars Climate Orbiter carried two scientific instruments for measuring conditions in Mars's atmosphere. The Pressure Modulator Infrared Radiometer (PMIRR) was to measure the temperature of Mars's atmosphere and observe the concentration of dust and water vapor in the atmosphere. The second instrument, the Mars Color Imager (MARCI), consisted of a wide-angle camera and a medium-angle camera. The cameras were to gather images in visual light and ultraviolet radiation. Visual light and ultraviolet radiation are different types of electromagnetic energy (vibrating electric and magnetic waves). MARCI weighed only 1 kg (2 lb), making it the lightest camera ever sent to Mars. Mars Climate Orbiter traveled to Mars without any apparent mishap, reaching the planet in September 1999. Just as it was supposed to enter orbit around Mars on September 23, however, navigators lost touch with the spacecraft. Investigations of the failure revealed that two different teams working on the spacecraft had used two different systems of units for the same measurement. Engineers at Lockheed Martin Aeronautics in Denver, Colorado, had built the spacecraft and used the English unit of pounds-seconds to describe the power of the spacecraft's thrusters. Meanwhile, scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, had used the metric unit of newton-seconds for thrust power in their calculations of the spacecraft's trajectory. The difference in units led to a miscalculation of the orbiter's trajectory. Because the thrusters contributed only a small amount to the spacecraft's trip, the mistake set the 670-million-km (416-million-mi) journey off by just 100 km (60 mi). However, the difference was enough to send the craft too close to the Martian surface, where it was destroyed by friction with the Martian atmosphere. In reaction to the loss of Mars Climate Orbiter, NASA appointed a board of investigators to look into factors that contributed to the mission's failure. The board found a fatal lack of communication between the company that had built the spacecraft and the company running the mission. While previous missions to Mars involved spacecraft built and run by Jet Propulsion Laboratory, NASA tried to save money on the Mars Climate Orbiter mission by contracting out the building of the spacecraft to Lockheed Martin. Another significant factor was that the mission used computer software that was not robust enough to find discrepancies in the expected and actual calculations of the spacecraft's path. Many experts attributed these and other factors that contributed to the mission's failure to a lack of sufficient funding. The mission cost NASA $125 million, less than half that of its predecessor, Mars Global Surveyor. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

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