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The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). The GPS uses a constellation of between 24 and 32 Medium Earth Orbit satellites that transmit precise microwave signals, that enable GPS receivers to determine their location, speed, direction, and time. GPS was developed by the United States Department of Defense. Its official name is NAVSTAR-GPS. Although NAVSTAR-GPS is not an acronym^[1], a few backronyms have been created for it^[2]. The GPS satellite constellation is managed by the United States Air Force 50th Space Wing.

Similar satellite navigation systems include the Russian GLONASS (incomplete as of 2008), the upcoming European Galileo positioning system, the proposed COMPASS navigation system of China, and IRNSS of India.

Following the shooting down of Korean Air Lines Flight 007 in 1983, President Ronald Reagan issued a directive making the system available free for civilian use as a common good.^[3] Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, scientific uses, and hobbies such as geocaching. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.

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Credit: Cmmmm

A scramjet (supersonic combustion ramjet) is a variation of a ramjet with the distinction being that some or all of the combustion process takes place supersonically. At higher speeds, it is necessary to combust supersonically to maximize the efficiency of the combustion process. Projections for the top speed of a scramjet engine (without additional oxidiser input) vary between Mach 12 and Mach 24 (orbital velocity).

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Selected biography

Christopher Columbus Kraft, Jr. (born February 28, 1924) is a retired NASA engineer and manager. After graduating from Virginia Tech in 1944, Kraft was hired by the National Advisory Committee for Aeronautics (NACA), the predecessor organization to the National Aeronautics and Space Administration (NASA). He worked for over a decade in aeronautical research before being asked in 1958 to join the Space Task Group, a small team entrusted with the responsibility of putting America's first man in space. Assigned to the flight operations division, Kraft became NASA's first flight director. He was on duty during such historic missions as America's first spaceflight, first orbital flight and first spacewalk.

At the beginning of the Apollo program Kraft retired as a flight director in order to concentrate on management and mission planning. In 1972 he became director of the Manned Spacecraft Center (later Johnson Space Center), following in the footsteps of his mentor Robert Gilruth. He held the position until his retirement from NASA in 1982. During his retirement, Kraft has consulted for numerous companies including IBM and Rockwell International, and he published an autobiography entitled Flight: My Life in Mission Control.

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