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Gravity Tractor
A gravity tractor is a theoretical spacecraft that would deflect another object in space, typically a potentially hazardous asteroid that might impact Earth, without physically contacting it, using only its gravitational field to transmit the required impulse. The gravitational force of a nearby space vehicle, though small, is able to alter the path of a much larger asteroid if the vehicle spends enough time close to it; all that is required is that the vehicle thrust in a consistent direction relative to the asteroid's path, and that neither the vehicle nor its expelled reaction mass come in direct contact with the asteroid. The tractor spacecraft could either hover near the object being deflected, or orbit it, directing its exhaust perpendicular to the plane of the orbit. The concept has two key advantages: namely that essentially nothing needs to be known about the mechanical composition and structure of the asteroid in advance; and that the relatively small amounts of force us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle (carrier rocket). On a sub-orbital spaceflight, a space vehicle enters space and then returns to the surface without having gained sufficient energy or velocity to make a full Earth orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies. Spacecraft used for human spaceflight carry people on board as crew or passengers from start or on orbit (space stations) only, whereas those used for robotic space missions operate either autonomously or telerobotically. Robotic spacecraft used to support scientific re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solar Sail
Solar sails (also known as light sails and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large mirrors. A number of spaceflight missions to test solar propulsion and navigation have been proposed since the 1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010. A useful analogy to solar sailing may be a sailing boat; the light exerting a force on the mirrors is akin to a sail being blown by the wind. High-energy laser beams could be used as an alternative light source to exert much greater force than would be possible using sunlight, a concept known as beam sailing. Solar sail craft offer the possibility of low-cost operations combined with long operating lifetimes. Since they have few moving parts and use no propellant, they can potentially be used numerous times for delivery of payloads. Solar sails use a phenomenon that has a proven, measured effect on astrodynamics. Solar pressure affec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asteroid Redirect Mission
The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013; the mission was later cancelled. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid. The spacecraft would characterize the asteroid and demonstrate at least one planetary defense technique before transporting the boulder to a stable lunar orbit, where it could be further analyzed both by robotic probes and by a future crewed mission, Asteroid Redirect Crewed Mission (ARCM). If funded, the mission would have launched in December 2021, with the additional objectives to test a number of new capabilities needed for future human expeditions to deep space, including advanced ion thrusters. The proposed 2018 NASA budget called for its cancellation, the missio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Normal (geometry)
In geometry, a normal is an object such as a line, ray, or vector that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the (infinite) line perpendicular to the tangent line to the curve at the point. A normal vector may have length one (a unit vector) or its length may represent the curvature of the object (a ''curvature vector''); its algebraic sign may indicate sides (interior or exterior). In three dimensions, a surface normal, or simply normal, to a surface at point P is a vector perpendicular to the tangent plane of the surface at P. The word "normal" is also used as an adjective: a line ''normal'' to a plane, the ''normal'' component of a force, the normal vector, etc. The concept of normality generalizes to orthogonality (right angles). The concept has been generalized to differentiable manifolds of arbitrary dimension embedded in a Euclidean space. The normal vector space or normal space of a manifold at point P ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravitational Force
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a result, it has no significant influence at the level of subatomic particles. However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. On Earth, gravity gives weight to physical objects, and the Moon's gravity is responsible for sublunar tides in the oceans (the corresponding antipodal tide is caused by the inertia of the Earth and Moon orbiting one another). Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized. Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe2) as the lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is also used to search for hypothetical weakly interacting massive particles and as a propellant for ion thrusters in spacecraft. Naturally occurring xenon consists of seven stable isotopes and two long-lived radioactive isotopes. More than 40 unstable xenon isotopes undergo radioactive decay, and the isotope ratios of xenon are an important tool for studying the early history of the Solar System. Radioactive xenon-135 is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Newton (unit)
The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion. Definition A newton is defined as 1 kg⋅m/s (it is a derived unit which is defined in terms of the SI base units). One newton is therefore the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in the direction of the applied force. The units "metre per second squared" can be understood as measuring a rate of change in velocity per unit of time, i.e. an increase in velocity by 1 metre per second every second. In 1946, Conférence Générale des Poids et Mesures (CGPM) Resolution 2 standardized the unit of force in the MKS system of units to be the amount needed to accelerate 1 kilogram of mass at the rate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near-Earth Object
A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). If a NEO's orbit crosses the Earth's orbit, and the object is larger than across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets. There are over 30,503 known near-Earth asteroids (NEAs) and over a hundred known short-period near-Earth comets (NECs). A number of solar-orbiting meteoroids were large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the Earth. Asteroids as small as in diameter can cause significant damage to the local environment and human populations. Larger asteroids penetrate the atmosphere to the surf ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
WIRED
''Wired'' (stylized as ''WIRED'') is a monthly American magazine, published in print and online editions, that focuses on how emerging technologies affect culture, the economy, and politics. Owned by Condé Nast, it is headquartered in San Francisco, California, and has been in publication since March/April 1993. Several spin-offs have been launched, including ''Wired UK'', ''Wired Italia'', ''Wired Japan'', and ''Wired Germany''. From its beginning, the strongest influence on the magazine's editorial outlook came from founding editor and publisher Louis Rossetto. With founding creative director John Plunkett, Rossetto in 1991 assembled a 12-page prototype, nearly all of whose ideas were realized in the magazine's first several issues. In its earliest colophons, ''Wired'' credited Canadian media theorist Marshall McLuhan as its "patron saint". ''Wired'' went on to chronicle the evolution of digital technology and its impact on society. ''Wired'' quickly became recognized as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rusty Schweickart
Russell Louis "Rusty" Schweickart (also Schweikart; born October 25, 1935) is an American aeronautical engineer, and a former NASA astronaut, research scientist, U.S. Air Force fighter pilot, as well as a former business executive and government executive. Schweickart was selected in 1963 for NASA's third astronaut group. He was the Lunar Module Pilot on the 1969 Apollo 9 mission, the first crewed flight test of the lunar module, on which he performed the first in-space test of the portable life support system used by the Apollo astronauts who walked on the Moon. As backup Commander of the first crewed Skylab mission in 1973, he was responsible for developing the hardware and procedures used by the first crew to perform critical in-flight repairs of the Skylab station. After Skylab, he served for a time as Director of User Affairs in NASA's Office of Applications. Schweickart left NASA in 1977 to serve for two years as California Governor Jerry Brown's assistant for scie ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Orbital Stationkeeping
In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted. The deviation of Earth's gravity field from that of a homogeneous sphere and gravitational forces from the Sun and Moon will in general perturb the orbital plane. For a sun-synchronous orbit, the precession of the orbital plane caused by the oblateness of the Earth is a desirable feature that is part of mission design but the inclination change caused by the gravitational forces of the Sun and Moon is undesirable. For geostationary spacecraft, the inclination chang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Potentially Hazardous Object
A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are defined as having a minimum orbit intersection distance with Earth of less than and an absolute magnitude of 22 or brighter. More than 99% of the known potentially hazardous objects are not an impact threat over the next 100 years. , only 17 potentially hazardous objects are listed on the Sentry Risk Table as objects that are known not to be a threat over the next hundred years are excluded. Over hundreds if not thousands of years, "potentially hazardous" asteroids have the potential for their orbits to evolve to live up to their namesake. Most of these objects are potentially hazardous asteroids (PHAs), and a few are comets. there are 2,304 known PHAs (about 8% of the total near-Earth population), of which 153 are estimated to be larg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
