The four basic parts of a jet engine are the compressor, turbine, combustion chamber, and propelling nozzles. Air is compressed, then led through chambers where its volume is increased by the heat of fuel combustion. On emergence it spins the compression rotors, which in turn act on the incoming air.
In the cumbustion chamber of a jet propulsion engine the combustion of a fuel mixture generates expanding gases, which escape through an orifice to form the jet. Newton's third law of motion requires that the force that causes the high-speed motion of the jet of gas have a reaction force that is equal in magnitude and oppositely directed to push on the jet propulsion engine. Hence the term "reaction motor" is often applied to jet-propulsion engines.
The thermal jet engine operates with a continuous blast, but intermittent duct jet propulsion proceeds by a series of pulses, or intermittent explosions. The ramjet, or continuous duct, engine relies on its own forward motion to compress the air that enters it. Although highly efficient, it is designed to operate only after high speed has been attained through the use of some other power source, typically a rocket. The scramjet, or supersonic-combustion ramjet, engine is designed to operate at hypersonic speed (above Mach 5), using hydrogen for fuel; in theory, a scramjet-propelled craft could achieve orbital speed, with an efficiency three times that of liquid- or solid-fuel rockets. In addition, without the need to carry oxygen, an air-breathing, scramjet-powered vehicle can carry a greater payload than a rocket-powered one.
There are various thrust-augmentation methods that can be used to increase the effective driving force of jet engines: the afterburner, water-injection, and air bleed-off methods. An afterburner uses the exhaust gases from the engine for additional combustion, with resulting higher compression; however, it consumes large amounts of fuel. Injection of water into the air-compressor inlet also increases the thrust, but can be used only at take-off because of the high water consumption. Air bleed-off, sometimes called the fan augmentation method, also makes more efficient use of air otherwise wasted.
The first reaction engine, the aeolipile (a ball that rotated as a reaction to escaping steam), was constructed by the inventor Heron (or Hero) of Alexandria. Developments through the centuries have resulted in two general types of reaction machines, the true rocket and the airstream engine, commonly known as the jet engine. Unlike a jet engine, a rocket engine carries with it chemicals that enable it to burn its fuel without drawing air from an outside source. Thus a rocket can operate in outer space, where there is no atmosphere. Fritz von Opel, a German automobile manufacturer, made the first flight entirely by rocket power in 1939. The American R. H. Goddard did much of the important pioneer work in modern rocket development.
The second category of reaction motor, the jet engine, is a development of the late 18th-century gas turbine engines, which directed combustion gases against the blades of a turbine wheel. Not until 1908 was it suggested that an aircraft could be driven by jet propulsion. René Lorin, a French engineer, proposed using a reciprocating engine to compress air, mix it with fuel, and thus propel the aircraft by the pulses of hot gas produced by combustion of the mixture. Henri Coanda, a Romanian engineer, experimented with a reaction-powered aircraft in 1910, and observed the phenomenon now known as the Coanda effect. In 1939 the English engineer Frank Whittle developed a jet engine that powered a full-sized aircraft, and a year later Secundo Campini in Italy flew for 10 min using a thermal jet engine.
Jet-propelled aircraft have replaced propeller-driven types in all but short-range commercial applications; turboprop planes, in which a propeller is turned by a turbine engine, are used for short-range flights. The SR-71 Blackbird, a U.S. jet spyplane, holds the current speed record of 2,193.17 mph (3,529.56 kph) for a piloted air-breathing airplane, but NASA's experimental scramjet-powered pilotless X-43A bested this, almost reaching Mach 7 (about 5,000 mph/8,000 kph) and Mach 10 (about 6,800 mph/11,000 kph) in brief test flights in 2004. The Australian-led HyShot Flight Program successfully tested a British-designed scramjet engine in 2006.
Jet Propulsion Laboratory (JPL) is a NASA research center located in the cities of Pasadena and La Cañada Flintridge, near Los Angeles, California, USA. Managed by the California Institute of Technology (Caltech), it builds and operates unmanned spacecraft for the National Aeronautics and Space Administration (NASA). Among its current projects are the Cassini-Huygens mission to Saturn, the Mars Reconnaissance Orbiter, and the Spitzer Space Telescope.
By 1958, JPL's government affiliation was transferred to the new National Aeronautics and Space Administration (NASA), and JPL's current mission of unmanned spaceflight began. JPL engineers designed and built the Explorers, the U.S.'s first artificial satellites, as well as the unmanned Ranger and Surveyor missions to the Moon that prepared the way for Apollo. JPL also led the way in interplanetary exploration with the Mariner missions to Venus, Mars, and Mercury. In the 1970s, the more sophisticated Viking missions were sent to Mars, and the Voyager missions were sent to Jupiter, Saturn, and beyond. The 1990s saw the Magellan mission to map Venus, the Galileo mission to orbit and intensively study Jupiter, and a new array of Mars missions including Mars Pathfinder and Mars Global Surveyor. Currently, JPL operates the Cassini-Huygens mission to orbit and intensively study Saturn, the Stardust mission to collect cometary dust, the Spitzer Space Telescope, and three missions currently at Mars (Mars Odyssey, the Mars Exploration Rovers, and Mars Reconnaissance Orbiter).
Almost all of the of the U.S. federal government/NASA owned property that makes up the JPL campus is actually located in the city of La Cañada Flintridge, California, but it maintains a Pasadena address (4800 Oak Grove Drive, Pasadena, CA 91109). The city of La Cañada Flintridge, California was incorporated in 1976, well after JPL attained international recognition with a Pasadena address. Reasons for retaining the Pasadena address may include consistency over time, consistency with Caltech (most employees are Caltech employees and JPL is managed for NASA by Caltech), greater national and international recognition of the place name (relating in part to the Rose Bowl and the Rose Parade), and the simplicity of the address given that La Cañada Flintridge is one of the longest city names in the United States. There has been periodic conflict between the two cities over the issue of which should be mentioned in the media as the home of the laboratory.
On August 30, 2007, a group of JPL employees filed suit in federal court against NASA, Caltech, and the Department of Commerce, claiming their Constitutional rights were being violated by new background investigations. Employees were told that if they did not sign an unlimited waiver of privacy , they would be deemed to have "voluntarily resigned. Ostensibly, the rebadging rules were designed to make JPL compliant with FIPS 201. The United States Court of Appeals for the Ninth Circuit found the process violated the employees' privacy rights and has issued a preliminary injunction .
The lab has an open house once a year on a Saturday and Sunday in May, when the public is invited to tour the facilities and see live demonstrations of JPL science and technology. More limited private tours are also available throughout the year if scheduled well in advance. Thousands of schoolchildren from Southern California and elsewhere visit the lab every year.
The 2008 Open House took place on May 3rd and 4th. To learn more, go to jpl.nasa.gov
Interview: Randi Wessen discusses the tradition of Jet Propulsion Laboratory employees using peanuts as good luck charms
Jul 01, 2004; MICHELE NORRIS All Things Considered (NPR) 07-01-2004 Interview: Randi Wessen discusses the tradition of Jet Propulsion...