|
Laser Propulsion
Laser propulsion is a form of beam-powered propulsion where the energy source is a remote (usually ground-based) laser system and separate from the reaction mass. This form of propulsion differs from a conventional chemical rocket where both energy and reaction mass come from the solid or liquid propellants carried on board the vehicle. History The basic concepts underlying a photon-propelled "sail" propulsion system were developed by Eugene Sanger and the Hungarian physicist György Marx. Propulsion concepts using laser-energized rockets were developed in the 1970s by Arthur Kantrowitz and Wolfgang Moekel, with a variant using laser ablation pioneered by Leik Myrabo.Myrabo, L.N. 1976MHD propulsion by absorption of laser radiation" ''Journal of Spacecraft and Rockets", Vol. 13, 8, pp. 466–472. doi 10.2514/3.27919 An exposition of Kantrowitz's laser propulsion ideas was published in 1988. Laser propulsion systems may transfer momentum to a spacecraft in two different ways. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beam-powered Propulsion
Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a laser beam and it is either pulsed or continuous. A continuous beam lends itself to thermal rockets, photonic thrusters and light sails, whereas a pulsed beam lends itself to ablative thrusters and pulse detonation engines. The rule of thumb that is usually quoted is that it takes a megawatt of power beamed to a vehicle per kg of payload while it is being accelerated to permit it to reach low earth orbit. Other than launching to orbit, applications for moving around the world quickly have also been proposed. Background Rockets are momentum machines; they use mass ejected from the rocket to provide momentum to the rocket. Momentum is the product of mass and velocity, so rockets generally attempt to put as much velocity into their worki ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geoffrey A
Geoffrey, Geoffroy, Geoff, etc., may refer to: People * Geoffrey (name), including a list of people with the name * Geoffroy (surname), including a list of people with the name * Geoffrey of Monmouth (c. 1095–c. 1155), clergyman and one of the major figures in the development of British history * Geoffrey I of Anjou (died 987) * Geoffrey II of Anjou (died 1060) * Geoffrey III of Anjou (died 1096) * Geoffrey IV of Anjou (died 1106) * Geoffrey V, Count of Anjou (1113–1151), father of King Henry II of England * Geoffrey II, Duke of Brittany (1158–1186), one of Henry II's sons * Geoffrey, Archbishop of York (c. 1152–1212) * Geoffroy du Breuil of Vigeois, 12th century French chronicler * Geoffroy de Charney (died 1314), Preceptor of the Knights Templar * Geoffroy IV de la Tour Landry (c. 1320–1391), French nobleman and writer * Geoffrey the Baker (died c. 1360), English historian and chronicler * Geoffroy (musician) (born 1987), Canadian singer, songwriter and multi-instrum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nuclear Thermal Rocket
A nuclear thermal rocket (NTR) is a type of thermal rocket where the heat from a nuclear reaction, often nuclear fission, replaces the chemical energy of the propellants in a chemical rocket. In an NTR, a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor and then expands through a rocket nozzle to create thrust. The external nuclear heat source theoretically allows a higher effective exhaust velocity and is expected to double or triple payload capacity compared to chemical propellants that store energy internally. NTRs have been proposed as a spacecraft propulsion technology, with the earliest ground tests occurring in 1955. The United States maintained an NTR development program through 1973 when it was shut down for various reasons, for example to focus on Space Shuttle development. Although more than ten reactors of varying power output have been built and tested, , no nuclear thermal rocket has flown. Whereas all early applicat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Rocket
A thermal rocket is a rocket engine that uses a propellant that is externally heated before being passed through a nozzle to produce thrust, as opposed to being internally heated by a redox (combustion) reaction as in a chemical rocket. Thermal rockets can theoretically give high performance, depending on the fuel used and design specifications, and a great deal of research has gone into a variety of types. However, aside from the simple cold gas thruster and steam rocket, none have proceeded past the testing stage. Theory For a rocket engine, the efficiency of propellant use (the amount of impulse produced per mass of propellant) is measured by the specific impulse (I_), which is proportional to the effective exhaust velocity. For thermal rocket systems, the specific impulse increases as the square root of the temperature, and inversely as the square root of the molecular mass of the exhaust. In the simple case where a thermal source heats an ideal Monatomic gas reaction mass, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large observatories were built in the United States with the aim of detecting gravitational waves by laser interferometry. These observatories use mirrors spaced four kilometers apart which are capable of detecting a change of less than one ten-thousandth the charge diameter of a proton. (that is, to Proxima Centauri at ). The initial LIGO observatories were funded by the United States National Science Foundation (NSF) and were conceived, built and are operated by Caltech and MIT. They collected data from 2002 to 2010 but no gravitational waves were detected. The Advanced LIGO Project to enhance the original LIGO detectors began in 2008 and continues to be supported by the NSF, with important contributions from the United Kingdom's Science ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fabry–Pérot Interferometer
In optics, a Fabry–Pérot interferometer (FPI) or etalon is an optical cavity made from two parallel reflecting surfaces (i.e.: thin mirrors). Optical waves can pass through the optical cavity only when they are in resonance with it. It is named after Charles Fabry and Alfred Perot, who developed the instrument in 1899. ''Etalon'' is from the French ''étalon'', meaning "measuring gauge" or "standard". Etalons are widely used in telecommunications, lasers and spectroscopy to control and measure the wavelengths of light. Recent advances in fabrication technique allow the creation of very precise tunable Fabry–Pérot interferometers. The device is technically an interferometer when the distance between the two surfaces (and with it the resonance length) can be changed, and an etalon when the distance is fixed (however, the two terms are often used interchangeably). Basic description The heart of the Fabry–Pérot interferometer is a pair of partially reflective glass ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Breakthrough Starshot
Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a Proof of concept, proof-of-concept fleet of light sail interstellar probes named ''Starchip'', to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg. A flyby mission has been proposed to Proxima Centauri b, an Terrestrial planet, Earth-sized exoplanet in the habitable zone of its host star, Proxima Centauri, in the Alpha Centauri system. At a speed between 15% and 20% of the speed of light, it would take between twenty and thirty years to complete the journey, and approximately four years for a return message from the starship to Earth. The conceptual principles to enable this interstellar travel project were described in "A Roadmap to Interstellar Flight", by Philip Lubin of University of California, Santa Barbara, UC Santa Barbara.(file available at University ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phased Array
In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving the antennas. In a simple array antenna, the radio frequency current from the transmitter is fed to multiple individual antenna elements with the proper phase relationship so that the radio waves from the separate elements combine ( superpose) to form beams, to increase power radiated in desired directions and suppress radiation in undesired directions. In a phased array, the power from the transmitter is fed to the radiating elements through devices called ''phase shifters'', controlled by a computer system, which can alter the phase or signal delay electronically, thus steering the beam of radio waves to a different direction. Since the size of an antenna array must extend many wavelengths to achieve the high gain needed for narrow bea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sample-return Mission
A sample-return mission is a spacecraft mission to collect and return samples from an extraterrestrial location to Earth for analysis. Sample-return missions may bring back merely atoms and molecules or a deposit of complex compounds such as loose material and rocks. These samples may be obtained in a number of ways, such as soil and rock excavation or a collector array used for capturing particles of solar wind or cometary debris. Nonetheless, concerns have been raised that the return of such samples to planet Earth may endanger Earth itself. To date, samples of Moon rock from Earth's Moon have been collected by robotic and crewed missions, the comet Wild 2 and the asteroids 25143 Itokawa and 162173 Ryugu have been visited by robotic spacecraft which returned samples to Earth, and samples of the solar wind have been returned by the robotic ''Genesis'' mission. Samples from the asteroid 101955 Bennu are en route back to Earth and are expected to arrive in September 2023. I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flyby (spaceflight)
A flyby () is a spaceflight operation in which a spacecraft passes in proximity to another body, usually a target of its space exploration mission and/or a source of a gravity assist to impel it towards another target. Spacecraft which are specifically designed for this purpose are known as flyby spacecraft, although the term has also been used in regard to asteroid flybys of Earth for example. Important parameters are the time and distance of closest approach. Spacecraft flyby Flyby maneuvers can be conducted with a planet, a natural satellite or a non-planetary object such as a small Solar System body. Planetary flybys have occurred with Mars or Earth for example: *List of Earth flybys * Mars flyby An example of a comet flyby is when International Cometary Explorer (formerly ISEE-3) passed about from the nucleus of Comet Giacobini-Zinner in September 1985. Another application of the flyby is of Earth's Moon, usually called a lunar flyby. The Apollo 13 spacecraft had an exp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interplanetary Travel
Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars, Venus and Mercury. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe. A number of techniques have been developed to make interplanetary flights more economical. Advanc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a secondary source of the propagating wave. Italian scientist Francesco Maria Grimaldi coined the word ''diffraction'' and was the first to record accurate observations of the phenomenon in 1660. In classical physics, the diffraction phenomenon is described by the Huygens–Fresnel principle that treats each point in a propagating wavefront as a collection of individual spherical wavelets. The characteristic bending pattern is most pronounced when a wave from a coherent source (such as a laser) encounters a slit/aperture that is comparable in size to its wavelength, as shown in the inserted image. This is due to the addition, or interference, of different points on the wavefront (or, equivalently, each wavelet) that travel by paths of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
.png "Click for more on -> Flyby (spaceflight)")
