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Theoretical spacecraft propulsion refers to a series of theoretical spacecraft propulsion systems mainly proposed for interstellar travel.
The fission sail is a type of spacecraft propulsion proposed by Robert Forward that uses fission fragments to propel a large solar sail-like craft. It is similar in concept to the fission-fragment rocket in that the fission by-products are directly harnessed as working mass, and differs primarily in the way that the fragments are used for thrust.
In the fission sail, the "rocket" is built in the form of a two-layer sheet, with some sort of absorber on one side, and nuclear fuel on the other. Atoms in the fuel that decay will release their fragments in random, but opposite, directions. In the simple case where the decay releases the fragments "front" and "rear", the rearward moving fragment generates thrust directly, while the frontward moving one is absorbed in the front half of the sail with no net contribution to thrust. The sail is not a nuclear reactor, and relies on natural decay rates for energy release. The thrust from such a system will always be very low, albeit extremely efficient.
Forward proposed the system as an "add on" to existing solar sails. Close to stars where the light density is high the sails work fine, but as they move past about 2 AU their thrust is too low to be useful. Forward suggested that coating the sail with fissionable material would provide thrust in this region, where maneuvering is no longer as important. Such a system would accelerate and maneuver based on solar energy for the start of its flight, and then continue to accelerate at a lower rate for long periods of time.
The term gravitational shielding refers to a hypothetical process of shielding an object from the influence of a gravitational field. Such processes, if they existed, would have the effect of reducing the weight of an object. The shape of the shielded region would be similar to a shadow from the gravitational shield. For example, the shape of the shielded region above a disk would be conical. The height of the cone's apex above the disk would vary directly with the height of the shielding disk above the earth. [1] Experimental evidence to date indicates that no such effect exists. Gravitational shielding is considered to be a violation of the equivalence principle and therefore inconsistent with both Newtonian theory and general relativity. [2]
The concept of gravity shielding is a common concept in science fiction literature, especially for space travel. One of the first and best known examples is the fictional gravity shielding substance "Cavorite" that appears in H. G. Wells's classic 1901 novel The First Men in the Moon . Wells was promptly criticized for using it by Jules Verne. [3]
The Nano electrokinetic thruster is a theoretical space propulsion system based on the principle of electro-osmosis (also electroosmotic flow). It allows for a high specific impulse and high thrust-to-power ratio as well as a high final velocity which makes it suitable for a wide variety of applications. Due to difficulties in the production of the needed carbon nanotubes experimental testing has not yet started. [4]
The principle of electro-osmosis or electroosmotic flow creates a flow of an electrolyte through a very small tube in the nano-meter range. To achieve this flow there is a cathode and an anode at the ends of the tube over which a voltage is applied. Due to this voltage the ions in the electrolyte stored in a reservoir directly connected to the tube can be accelerated and ejected. This way electrical energy is transformed into kinetic energy. The amount of thrust created by one nano thruster is in the micro newton range, however due to its size it makes sense to arrange a large number in an array to achieve sufficient thrust. The thrust, exit velocity of the ions and the mass flow rate of the electrolyte are influenced by the applied voltage which makes it easy to regulate those parameters. The applied voltage and the pH-value of the electrolyte (amount of ions it contains) also vary the balance between thrust, efficiency and maximal exhaust velocity (determines the maximal achievable flight velocity). It is also theoretically possible to achieve a very high efficiency of nearly 100% [5] as well as a high specific impulse and high thrust-to-power ratio. This system has not yet been built and experimentally tested because of difficulties with the production of the nano-tubes needed for it. [4]
Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 55 astronomical units (AU), stars are typically separated by hundreds of thousands of AU, causing these distances to typically be expressed instead in light-years. Because of the vastness of these distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer.
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.
An ion thruster, ion drive, or ion engine is a form of electric propulsion used for spacecraft propulsion. An ion thruster creates a cloud of positive ions from a neutral gas by ionizing it to extract some electrons from its atoms. The ions are then accelerated using electricity to create thrust. Ion thrusters are categorized as either electrostatic or electromagnetic.
A pulsed plasma thruster (PPT), also known as a plasma jet engine, is a form of electric spacecraft propulsion. PPTs are generally considered the simplest form of electric spacecraft propulsion and were the first form of electric propulsion to be flown in space, having flown on two Soviet probes starting in 1964. PPTs are generally flown on spacecraft with a surplus of electricity from abundantly available solar energy.
A nuclear electric rocket is a type of spacecraft propulsion system where thermal energy from a nuclear reactor is converted to electrical energy, which is used to drive an ion thruster or other electrical spacecraft propulsion technology. The nuclear electric rocket terminology is slightly inconsistent, as technically the "rocket" part of the propulsion system is non-nuclear and could also be driven by solar panels. This is in contrast with a nuclear thermal rocket, which directly uses reactor heat to add energy to a working fluid, which is then expelled out of a rocket nozzle.
In a traditional nuclear photonic rocket, an onboard nuclear reactor would generate such high temperatures that the blackbody radiation from the reactor would provide significant thrust. The disadvantage is that it takes much power to generate a small amount of thrust this way, so acceleration is very low. The photon radiators would most likely be constructed using graphite or tungsten. Photonic rockets are technologically feasible, but rather impractical with current technology based on an onboard nuclear power source.
Field-emission electric propulsion (FEEP) is an advanced electrostatic space propulsion concept, a form of ion thruster, that uses a liquid metal as a propellant – usually either caesium, indium, or mercury.
The Biefeld–Brown effect is an electrical phenomenon that produces an ionic wind that transfers its momentum to surrounding neutral particles. It describes a force observed on an asymmetric capacitor when high voltage is applied to the capacitor's electrodes. Once suitably charged up to high DC potentials, a thrust at the negative terminal, pushing it away from the positive terminal, is generated. The effect was named by inventor Thomas Townsend Brown who claimed that he did a series of experiments with professor of astronomy Paul Alfred Biefeld, a former teacher of Brown whom Brown claimed was his mentor and co-experimenter at Denison University in Ohio.
The Breakthrough Propulsion Physics Project (BPP) was a research project funded by NASA from 1996 to 2002 to study various proposals for revolutionary methods of spacecraft propulsion that would require breakthroughs in physics before they could be realized. The project ended in 2002, when the Advanced Space Transportation Program was reorganized and all speculative research was cancelled. During its six years of operational funding, this program received a total investment of $1.2 million.
Anti-gravity is a hypothetical phenomenon of creating a place or object that is free from the force of gravity. It does not refer to either the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism and aerodynamic lift. Anti-gravity is a recurring concept in science fiction. Examples are the gravity blocking substance "Cavorite" in H. G. Wells's The First Men in the Moon and the Spindizzy machines in James Blish's Cities in Flight.
BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. The mission comprises two satellites launched together: the Mercury Planetary Orbiter (MPO) and Mio. The mission will perform a comprehensive study of Mercury, including characterization of its magnetic field, magnetosphere, and both interior and surface structure. It was launched on an Ariane 5 rocket on 20 October 2018 at 01:45 UTC, with an arrival at Mercury planned for on 5 December 2025, after a flyby of Earth, two flybys of Venus, and six flybys of Mercury. The mission was approved in November 2009, after years in proposal and planning as part of the European Space Agency's Horizon 2000+ programme; it is the last mission of the programme to be launched.
In spaceflight, an orbital maneuver is the use of propulsion systems to change the orbit of a spacecraft. For spacecraft far from Earth an orbital maneuver is called a deep-space maneuver (DSM).
An ion-propelled aircraft or ionocraft is an aircraft that uses electrohydrodynamics (EHD) to provide lift or thrust in the air without requiring combustion or moving parts. Current designs do not produce sufficient thrust for manned flight or useful loads.
This is an alphabetical list of articles pertaining specifically to aerospace engineering. For a broad overview of engineering, see List of engineering topics. For biographies, see List of engineers.
The term gravitational shielding refers to a hypothetical process of shielding an object from the influence of a gravitational field. Such processes, if they existed, would have the effect of reducing the weight of an object. The shape of the shielded region would be similar to a shadow from the gravitational shield. For example, the shape of the shielded region above a disk would be conical. The height of the cone's apex above the disk would vary directly with the height of the shielding disk above the Earth. Experimental evidence to date indicates that no such effect exists. Gravitational shielding is considered to be a violation of the equivalence principle and therefore inconsistent with both Newtonian theory and general relativity.
A plasma propulsion engine is a type of electric propulsion that generates thrust from a quasi-neutral plasma. This is in contrast with ion thruster engines, which generate thrust through extracting an ion current from the plasma source, which is then accelerated to high velocities using grids/anodes. These exist in many forms. However, in the scientific literature, the term "plasma thruster" sometimes encompasses thrusters usually designated as "ion engines".
Spacecraft electric propulsion is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed and thus generating thrust to modify the velocity of a spacecraft in orbit. The propulsion system is controlled by power electronics.
The Nano electrokinetic thruster is a theoretical space propulsion system based on the principle of electro-osmosis. It allows for a high specific impulse and high thrust-to-power ratio as well as a high final velocity which makes it suitable for a wide variety of applications. Due to difficulties in the production of the needed carbon nanotubes experimental testing has not yet started.
The NASA Solar Technology Application Readiness (NSTAR) is a type of spacecraft ion thruster called electrostatic ion thruster. It is a highly efficient low-thrust spacecraft propulsion running on electrical power generated by solar arrays. It uses high-voltage electrodes to accelerate ions with electrostatic forces.
Microwave electrothermal thruster, also known as MET, is a propulsion device that converts microwave energy into thermal energy. These thrusters are predominantly used in spacecraft propulsion, more specifically to adjust the spacecraft’s position and orbit. A MET sustains and ignites a plasma in a propellant gas. This creates a heated propellant gas which in turn changes into thrust due to the expansion of the gas going through the nozzle. A MET’s heating feature is like one of an arc-jet ; however, due to the free-floating plasma, there are no problems with the erosion of metal electrodes, and therefore the MET is more efficient.