jet propulsion

jet propulsion

jet propulsion, propulsion of a body by a force developed in reaction to the ejection of a high-speed jet of gas.

Jet Propulsion Engines

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.

Development of the Reaction Engine

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.

JPL's Space Flight Operations Facility and Twenty-five-foot Space Simulator are designated National Historic Landmarks.


JPL dates back to the 1930s, when Caltech professor Theodore von Kármán began running rocket propulsion experiments at the Guggenheim Aeronautical Laboratory on the site. JPL was co-founded in 1944 with rocket scientists Tsien Hsue-shen and Jack Parsons, which has led some to affectionately refer to it as the Jack Parsons Lab. Despite its name, JPL has always been focused on developing and building rocket engines, not turbojets or other air-breathing jet engines; rockets were often called "jets" or "ramjets" before the mid-1940s. During World War II, the United States Army Air Forces asked JPL to analyze the V2 rockets that were developed by Nazi Germany, as well as work on other projects for the war effort.

From this study, JPL developed the Corporal missile. This project later evolved into the Sergeant Rocket until it was discontinued in 1977.

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.


There are approximately 5,000 full-time Caltech employees, and typically a few thousand additional contractors working on any given day. NASA also has a resident office at the facility staffed by federal managers who oversee JPL's activities and work for NASA. There are also some Caltech graduate students, college student interns and co-op students. Caltech and JPL jointly offer research opportunities for students, such as the SURF program (Summer Undergraduate Research Fellowship).

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 .

Open House days

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 2007 Open House took place on May 19-20, 2007 and featured new missions like Dawn Mission and Juno.

The 2008 Open House took place on May 3rd and 4th. To learn more, go to

Planetary Science Summer School

The Planetary Science Summer School (PSSS) is an annual workshop sponsored by the Jet Propulsion Laboratory. The program involves an one-week team design exercise developing an early mission concept study, working with JPL's Advanced Projects Design Team ("Team X") and other concurrent engineering teams.

Other works

In addition to its government work, JPL has also assisted the nearby motion picture and television industries, by advising them about scientific accuracy in their productions. Science fiction shows advised by JPL include Babylon 5 and its sequel series Crusade.


JPL is a federally funded research and development center (FFRDC) managed and operated by Caltech under a contract from NASA. JPL-run projects include the Galileo mission to Jupiter and its moons, the Mars rovers (including the 1997 Mars Pathfinder and the twin 2003 Mars Exploration Rovers). JPL has sent unmanned missions to every planet in our Solar System. JPL has also conducted extensive mapping missions of Earth. JPL manages the world-wide Deep Space Network, with facilities in California's Mojave Desert, in Spain near Madrid, and in Australia near Canberra.

Peanuts Tradition

There is a tradition at JPL to eat "good luck peanuts" before critical mission events, such as orbital insertions or landings. As the story goes, after the Ranger program had experienced failure after failure during the 1960s, the first successful mission of the Ranger program landed on the Moon while a JPL staffer was munching on peanuts. The staff jokingly decided that the peanuts must have been a good luck charm and the tradition persists today.


These are some of the missions partially sponsored by JPL

List of directors


The JPL Advanced Projects Design Team, also known as "Team X", is an interdisciplinary team of engineers that "utilizes concurrent engineering methodologies to complete rapid design, analysis and evaluation of mission concept designs". Current members include:

  • ACS - Peter Meakin and Sohrab Mobasser
  • CDS - James Naegle and Yutao He
  • Cost - Charles Baker
  • Deputy Systems - Sarah Hornbeck
  • EDL - William Strauss
  • Ground Systems - Susan Barry and Gregory Welz
  • Instruments - Marc Walch
  • Logistics - Melissa Vick
  • Mechanical - Steve Kondos
  • Mission Design - Try Lam

  • Planetary Protection - Laura Newlin
  • Power - Ronald Hall and Paul Stella
  • Risk - Julie Wertz and Samantha Infeld
  • Propulsion - Dick Cowley
  • Science - Bill Smythe and Kenneth Lawrence
  • Software - Cin-Young Lee
  • Systems - Stacey Boland
  • Telecom - David Hansen and Michael Pugh
  • Thermal - Donald Strayer
  • Comet Science - Paul Weissman


Further reading

  • MG Lord (2005). Astro Turf: The Private Life Of Rocket Science. New York: Walker & Company.

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