Misplaced Pages

#374625

96-491: The EmDrive is a concept for a thruster for spacecraft , first written about in 2001. It is purported to generate thrust by reflecting microwaves inside the device, in a way that would violate the law of conservation of momentum and other laws of physics . The concept has at times been referred to as a resonant cavity thruster . There is no official design for this device. Neither person who claims to have invented it has committed to an explanation for how it could operate as

192-432: A SpaceX Falcon 9 rocket. Rather than relying on high temperature and fluid dynamics to accelerate the reaction mass to high speeds, there are a variety of methods that use electrostatic or electromagnetic forces to accelerate the reaction mass directly, where the reaction mass is usually a stream of ions . Ion propulsion rockets typically heat a plasma or charged gas inside a magnetic bottle and release it via

288-460: A joint venture with Gilo Industries Group , a small UK aerospace company. The Cannae Drive (formerly Q-drive), is another implementation of this idea, with a relatively flat cavity rather than a truncated cone. It was designed by Guido Fetta in 2006 and promoted within the US through his company, Cannae LLC, since 2011. In 2016, Fetta announced plans to eventually launch a CubeSat satellite containing

384-551: A magnetic nozzle so that no solid matter needs to come in contact with the plasma. Such an engine uses electric power, first to ionize atoms, and then to create a voltage gradient to accelerate the ions to high exhaust velocities. For these drives, at the highest exhaust speeds, energetic efficiency and thrust are all inversely proportional to exhaust velocity. Their very high exhaust velocity means they require huge amounts of energy and thus with practical power sources provide low thrust, but use hardly any fuel. Electric propulsion

480-449: A reaction mass and which produces thrust per Newton's third law of motion . All designs for electromagnetic propulsion operate on the principle of reaction mass. A hypothetical drive which did not expel propellant in order to produce a reaction force , providing thrust while being a closed system with no external interaction, would be a reactionless drive , violating the conservation of momentum and Newton's third law . Claims that

576-463: A 2014 follow-up experiment (published in 2016), Yang could not reproduce the 2010 observation and suggested it was due to experimental error. They had refined their experimental setup, using a three-wire torsion pendulum to measure thrust, and tested two different power setups. They concluded that they were unable to measure significant thrust; that "thrust" measured when using external power sources (as in their 2010 experiment) could be noise; and that it

672-532: A charged propellant. The benefit of this method is that it can achieve exhaust velocities, and therefore I sp {\displaystyle I_{\text{sp}}} , more than 10 times greater than those of a chemical engine, producing steady thrust with far less fuel. With a conventional chemical propulsion system, 2% of a rocket's total mass might make it to the destination, with the other 98% having been consumed as fuel. With an electric propulsion system, 70% of what's aboard in low Earth orbit can make it to

768-417: A deep-space destination. However, there is a trade-off. Chemical rockets transform propellants into most of the energy needed to propel them, but their electromagnetic equivalents must carry or produce the power required to create and accelerate propellants. Because there are currently practical limits on the amount of power available on a spacecraft, these engines are not suitable for launch vehicles or when

864-438: A diverse set of missions and destinations. Space exploration is about reaching the destination safely (mission enabling), quickly (reduced transit times), with a large quantity of payload mass, and relatively inexpensively (lower cost). The act of reaching the destination requires an in-space propulsion system, and the other metrics are modifiers to this fundamental action. Propulsion technologies can significantly improve

960-405: A drive is reactionless are generally considered by physicists to be pseudoscience . The first design of a resonant cavity thruster claiming to be a reactionless drive was by Roger Shawyer in 2001. He called his conical design an "EmDrive", and claimed that it produced thrust in the direction of the base of the cone. Guido Fetta later built a "Cannae Drive", based in part on Shawyer's concept, using

1056-473: A few have used electric propulsion such as ion thrusters and Hall-effect thrusters . Various technologies need to support everything from small satellites and robotic deep space exploration to space stations and human missions to Mars . Hypothetical in-space propulsion technologies describe propulsion technologies that could meet future space science and exploration needs. These propulsion technologies are intended to provide effective exploration of

SECTION 10

#1732780390375

1152-473: A fixed amount of reaction mass. The higher the specific impulse, the better the efficiency. Ion propulsion engines have high specific impulse (~3000 s) and low thrust whereas chemical rockets like monopropellant or bipropellant rocket engines have a low specific impulse (~300 s) but high thrust. The impulse per unit weight-on-Earth (typically designated by I sp {\displaystyle I_{\text{sp}}} ) has units of seconds. Because

1248-560: A given impulse with a large force over a short time or a small force over a long time. This means that for maneuvering in space, a propulsion method that produces tiny accelerations for a long time can often produce the same impulse as another which produces large accelerations for a short time. However, when launching from a planet, tiny accelerations cannot overcome the planet's gravitational pull and so cannot be used. Some designs however, operate without internal reaction mass by taking advantage of magnetic fields or light pressure to change

1344-438: A human spaceflight propulsion system to provide that acceleration continuously, (though human bodies can tolerate much larger accelerations over short periods). The occupants of a rocket or spaceship having such a propulsion system would be free from the ill effects of free fall , such as nausea, muscular weakness, reduced sense of taste, or leaching of calcium from their bones. The Tsiolkovsky rocket equation shows, using

1440-457: A large collection surface to function effectively. E-sails propose to use very thin and lightweight wires holding an electric charge to deflect particles, which may have more controllable directionality. Magnetic sails deflect charged particles from the solar wind with a magnetic field, thereby imparting momentum to the spacecraft. For instance, the so-called Magsail is a large superconducting loop proposed for acceleration/deceleration in

1536-430: A long period of time some form of propulsion is occasionally necessary to make small corrections ( orbital station-keeping ). Many satellites need to be moved from one orbit to another from time to time, and this also requires propulsion. A satellite's useful life is usually over once it has exhausted its ability to adjust its orbit. For interplanetary travel , a spacecraft can use its engines to leave Earth's orbit. It

1632-468: A major factor that needs to be taken into account for proper μN thrust measurements for these type of devices," and they planned on conducting future tests at higher power and at different frequencies, and with improved shielding and cavity geometry. In 2021, they revisited these experiments again and ran more precise tests. They reported with high confidence that the forces previously measured could be completely explained by experimental error, and that there

1728-457: A more precise suspension. They went on to publish two further papers, showing similar negative results for the laser-based LemDrive variant and Woodward's Mach-Effect thruster . In August 2016, Cannae announced plans to launch its thruster on a 6U cubesat which they would run for 6 months to observe how it functions in space. Cannae formed a company called Theseus for the venture and partnered with LAI International and SpaceQuest Ltd. to launch

1824-469: A new water-cooled prototype with increased thrust. He reported plans to have the device ready to use in space by May 2009 and to make the resonant cavity a superconductor, neither of which materialized. New Scientist magazine featured the EmDrive on the cover of 8 September 2006 issue. The article portrayed the device as plausible and emphasized the arguments of those who held that point of view. Egan ,

1920-566: A number of critical aspects of the mission. When launching a spacecraft from Earth, a propulsion method must overcome a higher gravitational pull to provide a positive net acceleration. When in space, the purpose of a propulsion system is to change the velocity, or v , of a spacecraft. In-space propulsion begins where the upper stage of the launch vehicle leaves off, performing the functions of primary propulsion , reaction control , station keeping , precision pointing , and orbital maneuvering . The main engines used in space provide

2016-410: A particle of reaction mass with mass m at velocity v is mv . But this particle has kinetic energy mv ²/2, which must come from somewhere. In a conventional solid , liquid , or hybrid rocket , fuel is burned, providing the energy, and the reaction products are allowed to flow out of the engine nozzle , providing the reaction mass. In an ion thruster , electricity is used to accelerate ions behind

SECTION 20

#1732780390375

2112-401: A pillbox-shaped cavity. Since 2008, a few physicists have tested their own models, trying to reproduce the results claimed by Shawyer and Fetta. Juan Yang at Xi'an 's Northwestern Polytechnical University (NWPU) was unable to reproducibly measure thrust from their models, over the course of 4 years. In 2016, Harold White 's group at NASA's Advanced Propulsion Physics Laboratory reported in

2208-436: A popular science fiction author, distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" made the magazine's coverage unreliable, sufficient "to constitute a real threat to the public understanding of science". Especially, Egan said he was "gobsmacked by the level of scientific illiteracy" in the magazine's coverage, alleging that it used "meaningless double-talk" to obfuscate

2304-672: A positive review publicly. In 2011, Fetta tested a superconducting version of the Cannae drive, suspended inside a liquid-helium-filled dewar , with inconclusive results. None of these results were published in the scientific literature, replicated by independent researchers, or replicated consistently by the inventors. In a few cases details were posted for a time on the inventors' websites, but no such documents remain online as of 2019. In 2015, Shawyer published an article in Acta Astronautica , summarising seven existing tests on

2400-438: A problem and this claim clearly flouted one of them   ... The Shawyer drive is as impossible as perpetual motion. Relativistic conservation of momentum has been understood for a century and dictates that if nothing emerges from Shawyer's device then its centre of mass will not accelerate. It is likely that Shawyer has used an approximation somewhere in his calculations that would have been reasonable if he hadn't then multiplied

2496-519: A rather different trajectory, either constantly thrusting against its direction of motion in order to decrease its distance from the Sun, or constantly thrusting along its direction of motion to increase its distance from the Sun. The concept has been successfully tested by the Japanese IKAROS solar sail spacecraft. Because interstellar distances are great, a tremendous velocity is needed to get

2592-597: A spacecraft needs a quick, large impulse, such as when it brakes to enter a capture orbit. Even so, because electrodynamic rockets offer very high I sp {\displaystyle I_{\text{sp}}} , mission planners are increasingly willing to sacrifice power and thrust (and the extra time it will take to get a spacecraft where it needs to go) in order to save large amounts of propellant mass. Spacecraft operate in many areas of space. These include orbital maneuvering, interplanetary travel, and interstellar travel. Artificial satellites are first launched into

2688-484: A spacecraft to its destination in a reasonable amount of time. Acquiring such a velocity on launch and getting rid of it on arrival remains a formidable challenge for spacecraft designers. No spacecraft capable of short duration (compared to human lifetime) interstellar travel has yet been built, but many hypothetical designs have been discussed. Spacecraft propulsion technology can be of several types, such as chemical, electric or nuclear. They are distinguished based on

2784-511: A thruster or what elements define it, making it hard to say definitively whether a given object is an example of an EmDrive. However, over the years, prototypes based on its public descriptions have been constructed and tested. In 2016, Harold White 's group at NASA observed a small apparent thrust from one such test, however subsequent studies suggested this was a measurement error caused by thermal gradients. In 2021, Martin Tajmar 's group at

2880-507: A thruster which produced 18 grams of thrust, and sent it to Boeing. Boeing did not license the technology and communication stopped. In 2012, a Boeing representative confirmed that Boeing Phantom Works used to explore exotic forms of space propulsion, including Shawyer's drive, but such work later ceased. They confirmed that "Phantom Works is not working with Mr. Shawyer," nor pursuing those explorations. In 2014, Shawyer presented ideas for 'second-generation' EmDrive designs and applications at

2976-520: A valid electro-magnetic theory behind a microwave resonant cavity thruster. A demonstration version of the drive was built and tested with different cavity shapes and at higher power levels in 2010. Using an aerospace engine test stand usually used to precisely test spacecraft engines like ion drives , they reported a maximum thrust of 720 mN at 2,500 W of input power. Yang noted that her results were tentative, and said she "[was] not able to discuss her work until more results are published". In

EmDrive - Misplaced Pages Continue

3072-497: A version of the Cannae Drive, which would run for 6 months to observe how it functions in space. No followup was published. In China, researchers working under Yang at NWPU built a resonant cavity thruster in 2008, and tested it for a number of years. A 2012 report claimed they had observed thrust, but in 2014 they found it to have been an experimental error. A second, improved prototype did not produce any measured thrust. At

3168-507: Is an equal and opposite reaction. Also, because force·velocity = power, any such device would violate conservation of energy when moving at a high enough velocity. The conservation of momentum is a symmetry of nature . An often-cited example of apparent nonconservation of momentum is the Casimir effect ; in the standard case where two parallel plates are attracted to each other. However the plates move in opposite directions, so no net momentum

3264-425: Is commonly used for station keeping on commercial communications satellites and for prime propulsion on some scientific space missions because of their high specific impulse. However, they generally have very small values of thrust and therefore must be operated for long durations to provide the total impulse required by a mission. The idea of electric propulsion dates to 1906, when Robert Goddard considered

3360-635: Is complex, but research has developed methods for their use in propulsion systems, and some have been tested in a laboratory. Here, nuclear propulsion moreso refers to the source of propulsion being nuclear, instead of a nuclear electric rocket where a nuclear reactor would provide power (instead of solar panels) for other types of electrical propulsion. Nuclear propulsion methods include: There are several different space drives that need little or no reaction mass to function. Many spacecraft use reaction wheels or control moment gyroscopes to control orientation in space. A satellite or other space vehicle

3456-528: Is extracted from the vacuum and, moreover, energy must be put into the system to take the plates apart again. Assuming homogeneous electric and magnetic fields, it is impossible for the EmDrive, or any other device, to extract a net momentum transfer from either a classical or quantum vacuum . Extraction of a net momentum "from nothing" has been postulated in an inhomogeneous vacuum, but this remains highly controversial as it will violate Lorentz invariance . Both Harold White's and Mike McCulloch's theories of how

3552-500: Is highly toxic and at risk of being banned across Europe. Non-toxic 'green' alternatives are now being developed to replace hydrazine. Nitrous oxide -based alternatives are garnering traction and government support, with development being led by commercial companies Dawn Aerospace, Impulse Space, and Launcher. The first nitrous oxide-based system flown in space was by D-Orbit onboard their ION Satellite Carrier ( space tug ) in 2021, using six Dawn Aerospace B20 thrusters, launched upon

3648-411: Is not explicitly necessary as the initial boost given by the rocket, gravity slingshot, monopropellant/bipropellent attitude control propulsion system are enough for the exploration of the solar system (see New Horizons ). Once it has done so, it must make its way to its destination. Current interplanetary spacecraft do this with a series of short-term trajectory adjustments. In between these adjustments,

3744-424: Is situated fairly deep in a gravity well ; the escape velocity required to leave its orbit is 11.2 kilometers/second. Thus for destinations beyond, propulsion systems need enough propellant and to be of high enough efficiency. The same is true for other planets and moons, albeit some have lower gravity wells. As human beings evolved in a gravitational field of "one g " (9.81m/s²), it would be most comfortable for

3840-462: Is still active as of this date). As further proof of the solar sail concept, NanoSail-D became the first such powered satellite to orbit Earth . As of August 2017, NASA confirmed the Sunjammer solar sail project was concluded in 2014 with lessons learned for future space sail projects. The U.K. Cubesail programme will be the first mission to demonstrate solar sailing in low Earth orbit, and

3936-561: Is subject to the law of conservation of angular momentum , which constrains a body from a net change in angular velocity . Thus, for a vehicle to change its relative orientation without expending reaction mass, another part of the vehicle may rotate in the opposite direction. Non-conservative external forces, primarily gravitational and atmospheric, can contribute up to several degrees per day to angular momentum, so such systems are designed to "bleed off" undesired rotational energies built up over time. The law of conservation of momentum

EmDrive - Misplaced Pages Continue

4032-463: Is then allowed to escape through a high-expansion ratio bell-shaped nozzle , a feature that gives a rocket engine its characteristic shape. The effect of the nozzle is to accelerate the mass, converting most of the thermal energy into kinetic energy, where exhaust speeds reaching as high as 10 times the speed of sound at sea level are common. The dominant form of chemical propulsion for satellites has historically been hydrazine , however, this fuel

4128-518: Is usually taken to imply that any engine which uses no reaction mass cannot accelerate the center of mass of a spaceship (changing orientation, on the other hand, is possible). But space is not empty, especially space inside the Solar System; there are gravitation fields, magnetic fields , electromagnetic waves , solar wind and solar radiation. Electromagnetic waves in particular are known to contain momentum, despite being massless; specifically

4224-696: The Journal of Propulsion and Power that a test of their own model had observed a small thrust. In late 2016, Yue Chen of the communication satellite division of the China Academy of Space Technology (CAST), said his team had tested prototypes, and would conduct in-orbit tests to determine if they could observe thrust. Martin Tajmar 's group at the Dresden University of Technology started testing prototypes in 2015, and by 2021 concluded that observations of thrust were false positives, reporting in

4320-457: The China Academy of Space Technology , Yue Chen filed several patent applications in 2016 describing various radio frequency (RF) resonant cavity thruster designs. These included a method for stacking several short resonant cavities to improve thrust, and a design with a cavity that was a semicylinder instead of a frustum. That December, Chen announced that CAST would conduct tests on a resonant cavity thruster in orbit, without specifying what design

4416-689: The Dresden University of Technology replicated White's test, observing apparent thrusts similar to those measured by the NASA team, and then made them disappear again when measured using point suspension. No other published experiment has measured apparent thrust greater than the experiment's margin of error. Tajmar's group published three papers in 2021 claiming that all published results showing thrust had been false positives, explaining each by outside forces. They concluded, "Our measurements refute all EmDrive claims by at least 3 orders of magnitude." Rocket engines operate by expelling propellant , which acts as

4512-486: The IEE . The technical director of EADS Astrium (Shawyer's former employer) denied this in the strongest terms, stating: I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way. None of the other alleged independent experts published

4608-727: The Oberth effect . A tether propulsion system employs a long cable with a high tensile strength to change a spacecraft's orbit, such as by interaction with a planet's magnetic field or through momentum exchange with another object. Beam-powered propulsion is another method of propulsion without reaction mass, and includes sails pushed by laser , microwave, or particle beams. Advanced, and in some cases theoretical, propulsion technologies may use chemical or nonchemical physics to produce thrust but are generally considered to be of lower technical maturity with challenges that have not been overcome. For both human and robotic exploration, traversing

4704-545: The Solar System and may permit mission designers to plan missions to "fly anytime, anywhere, and complete a host of science objectives at the destinations" and with greater reliability and safety. With a wide range of possible missions and candidate propulsion technologies, the question of which technologies are "best" for future missions is a difficult one; expert opinion now holds that a portfolio of propulsion technologies should be developed to provide optimum solutions for

4800-532: The quantum vacuum , and RF resonant cavity thrusters. In 2014, the group began testing resonant cavity thrusters, and in November 2016 they published a peer-reviewed paper on this work, in the Journal of Propulsion and Power . In July 2014, White reported tentative positive results for evaluating a tapered RF resonant cavity. Their first tests of this tapered cavity were conducted at very low power (2% of Shawyer's 2002 experiment). A net mean thrust over five runs

4896-545: The solar wind and deceleration in the Interstellar medium . A variant is the mini-magnetospheric plasma propulsion system and its successor, the magnetoplasma sail , which inject plasma at a low rate to enhance the magnetic field to more effectively deflect charged particles in a plasma wind. Japan launched a solar sail-powered spacecraft, IKAROS in May 2010, which successfully demonstrated propulsion and guidance (and

SECTION 50

#1732780390375

4992-473: The vacuum state . Such methods are highly speculative and include: A NASA assessment of its Breakthrough Propulsion Physics Program divides such proposals into those that are non-viable for propulsion purposes, those that are of uncertain potential, and those that are not impossible according to current theories. Below is a summary of some of the more popular, proven technologies, followed by increasingly speculative methods. Four numbers are shown. The first

5088-490: The "quantum vacuum virtual plasma", a new term he coined. Baez and Carroll criticized this explanation, because in the standard description of vacuum fluctuations, virtual particles do not behave as a plasma; Carroll also noted that the quantum vacuum has no "rest frame", providing nothing to push against, so it cannot be used for propulsion. In the same way, physicists James F. Woodward and Heidi Fearn published two papers showing that electron − positron virtual pairs of

5184-583: The CEAS Space Journal they had refuted all EmDrive claims by "at least 3 orders of magnitude." Media coverage of experiments using these designs has been polarized. The EmDrive first drew attention, both credulous and dismissive, when New Scientist wrote about it as an "impossible" drive in 2006. Media outlets were later criticized for misleading claims that a resonant cavity thruster had been "validated by NASA" following White's first tentative test reports in 2014. Scientists have continued to note

5280-508: The EmDrive could work rely on these asymmetric or dynamical Casimir effects . However, if these vacuum forces are present, they are expected to be exceptionally tiny based on our current understanding, too small to explain the level of observed thrust. In the event that observed thrust is not due to experimental error, a positive result could indicate new physics. In 2004, Shawyer claimed to have received seven independent positive reviews from experts at BAE Systems , EADS Astrium , Siemens and

5376-449: The EmDrive, the engine warms up. This also causes the fastening elements on the scale to warp, causing the scale to move to a new zero point. We were able to prevent that in an improved structure. Our measurements refute all EmDrive claims by at least 3 orders of magnitude. In 2001, Shawyer founded Satellite Propulsion Research Ltd , to work on the EmDrive, which he said used a resonant cavity to produce thrust without propellant. The company

5472-542: The EmDrive. Of these, four produced a measured force in the intended direction, three produced thrust in the opposite direction, and in one test thrust could be produced in either direction by varying the spring constants in the measuring apparatus. In 2008, a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at Northwestern Polytechnical University (NWPU) in Xi'an , China , said that they had developed

5568-613: The Institute of Aerospace Engineering at Technische Universität Dresden , Germany , concluded that the dominant effect underlying the apparent thrust could be clearly identified as an artifact caused by Earth's magnetic field interacting with power cables in the chamber, a result that other experts agree with. In March 2021, Tajmar's group published a definitive analysis of their own past experiments and those of others, showing that all could be explained by and reproduced via outside forces, refuting all EmDrive claims. When power flows into

5664-514: The amount of thrust that can be produced to a small value. Power generation adds significant mass to the spacecraft, and ultimately the weight of the power source limits the performance of the vehicle. Nuclear fuels typically have very high specific energy , much higher than chemical fuels, which means that they can generate large amounts of energy per unit mass. This makes them valuable in spaceflight, as it can enable high specific impulses , sometimes even at high thrusts. The machinery to do this

5760-430: The annual International Astronautical Congress . A paper based on his presentation was published in Acta Astronautica in 2015. While no functional prototype of the first-generation drive had yet been produced, it described a model for a superconducting resonant cavity and three models for thrusters with multiple cavities. In 2016, Shawyer filed further patents and launched a new company, Universal Propulsion Ltd. , as

5856-528: The change in momentum per unit of propellant used by a spacecraft, or the velocity of the propellant exiting the spacecraft, can be used to measure its "specific impulse." The two values differ by a factor of the standard acceleration due to gravity, g n , 9.80665 m/s² ( I sp g n = v e {\displaystyle I_{\text{sp}}g_{\mathrm {n} }=v_{e}} ). In contrast to chemical rockets, electrodynamic rockets use electric or magnetic fields to accelerate

SECTION 60

#1732780390375

5952-549: The desired altitude by conventional liquid/solid propelled rockets, after which the satellite may use onboard propulsion systems for orbital stationkeeping. Once in the desired orbit, they often need some form of attitude control so that they are correctly pointed with respect to the Earth , the Sun , and possibly some astronomical object of interest. They are also subject to drag from the thin atmosphere , so that to stay in orbit for

6048-451: The device because they thought it too contentious   ... The great thing is that Shawyer's ideas are testable. If he succeeds in getting his machine flown in space, we will know soon enough if it is ground-breaking device or a mere flight of fancy. New Scientist also published a letter from the former technical director of EADS Astrium : I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger

6144-458: The device. In 2018, they published results from an improved test rig, which showed that their measured thrust had been a result of experimental error from insufficiently shielded components interacting with the Earth's magnetic field. In new experiments, they measured thrust values consistent with previous experiments and again measured thrust perpendicular to the expected direction when the thruster

6240-434: The energy needed to generate thrust by chemical reactions to create a hot gas that is expanded to produce thrust . Many different propellant combinations are used to obtain these chemical reactions, including, for example, hydrazine , liquid oxygen , liquid hydrogen , nitrous oxide , and hydrogen peroxide . They can be used as a monopropellant or in bi-propellant configurations. Rocket engines provide essentially

6336-439: The first mission to demonstrate full three-axis attitude control of a solar sail. The concept of a gravitational slingshot is a form of propulsion to carry a space probe onward to other destinations without the expense of reaction mass; harnessing the gravitational energy of other celestial objects allows the spacecraft to gain kinetic energy. However, more energy can be obtained from the gravity assist if rockets are used via

6432-415: The highest specific powers and high specific thrusts of any engine used for spacecraft propulsion. Most rocket engines are internal combustion heat engines (although non-combusting forms exist). Rocket engines generally produce a high-temperature reaction mass, as a hot gas, which is achieved by combusting a solid, liquid or gaseous fuel with an oxidiser within a combustion chamber. The extremely hot gas

6528-560: The lack of unbiased coverage. In 2006, responding to the New Scientist piece, mathematical physicist John C. Baez at the University of California, Riverside , and Australian science-fiction writer Greg Egan , said the positive results reported by Shawyer were likely misinterpretations of experimental errors. In 2014, White's first conference paper suggested that resonant cavity thrusters could work by transferring momentum to

6624-455: The law of conservation of momentum , that for a rocket engine propulsion method to change the momentum of a spacecraft, it must change the momentum of something else in the opposite direction. In other words, the rocket must exhaust mass opposite the spacecraft's acceleration direction, with such exhausted mass called propellant or reaction mass . For this to happen, both reaction mass and energy are needed. The impulse provided by launching

6720-431: The micronewton level, atop an antivibration granite table at ambient air pressure; then on a torsion pendulum with a force resolution of 0.1 mN, inside a vacuum chamber at ambient air pressure and in a hard vacuum at 400 μPa (4 × 10 mbar). They used a conventional ISM band 2.45 GHz 700 W oven magnetron, and a small cavity with a low Q factor (20 in vacuum tests). They observed small positive thrusts in

6816-654: The momentum flux density P of an EM wave is quantitatively 1/c times the Poynting vector S , i.e. P = S /c , where c is the velocity of light. Field propulsion methods which do not rely on reaction mass thus must try to take advantage of this fact by coupling to a momentum-bearing field such as an EM wave that exists in the vicinity of the craft; however, because many of these phenomena are diffuse in nature, corresponding propulsion structures must be proportionately large. The concept of solar sails rely on radiation pressure from electromagnetic energy, but they require

6912-503: The orbit of its destination. The spacecraft falls freely along this elliptical orbit until it reaches its destination, where another short period of thrust accelerates or decelerates it to match the orbit of its destination. Special methods such as aerobraking or aerocapture are sometimes used for this final orbital adjustment. Some spacecraft propulsion methods such as solar sails provide very low but inexhaustible thrust; an interplanetary vehicle using one of these methods would follow

7008-806: The physics of the propulsion system and how thrust is generated. Other experimental and more theoretical types are also included, depending on their technical maturity. Additionally, there may be credible meritorious in-space propulsion concepts not foreseen or reviewed at the time of publication, and which may be shown to be beneficial to future mission applications. Almost all types are reaction engines , which produce thrust by expelling reaction mass , in accordance with Newton's third law of motion . Examples include jet engines , rocket engines , pump-jet , and more uncommon variations such as Hall–effect thrusters , ion drives , mass drivers , and nuclear pulse propulsion . A large fraction of rocket engines in use today are chemical rockets ; that is, they obtain

7104-447: The positive direction and negative thrusts in the negative direction, of about 20 μN in a hard vacuum. However, when they rotated the cavity upwards as a "null" configuration, they observed an anomalous thrust of hundreds of micronewtons, much larger than the expected result of zero thrust. This indicated a strong source of noise which they could not identify. This led them to conclude that they could not confirm or refute claims about

7200-542: The possibility in his personal notebook. Konstantin Tsiolkovsky published the idea in 1911. Electric propulsion methods include: For some missions, particularly reasonably close to the Sun, solar energy may be sufficient, and has often been used, but for others further out or at higher power, nuclear energy is necessary; engines drawing their power from a nuclear source are called nuclear electric rockets . Current nuclear power generators are approximately half

7296-420: The primary propulsive force for orbit transfer , planetary trajectories , and extra planetary landing and ascent . The reaction control and orbital maneuvering systems provide the propulsive force for orbit maintenance, position control, station keeping, and spacecraft attitude control. In orbit, any additional impulse , even tiny, will result in a change in the orbit path, in two ways: Earth's surface

7392-415: The problem of conservation of momentum. The letter was endorsed by Baez and posted on his blog. New Scientist editor Jeremy Webb responded to critics: It is a fair criticism that New Scientist did not make clear enough how controversial Roger Shawyer's engine is. We should have made more explicit where it apparently contravenes the laws of nature and reported that several physicists declined to comment on

7488-626: The quantum vacuum, discussed by White as a potential virtual plasma propellant, could not account for thrust in any isolated, closed electromagnetic system such as a quantum vacuum thruster . In 2015, physicists Eric W. Davis at the Institute for Advanced Studies in Austin and Sean M. Carroll at the California Institute of Technology concluded that the thrust measurements reported in papers by both Tajmar and White were indicative of thermal effect errors. In May 2018, researchers from

7584-550: The result by 50,000. The reason physicists value principles such as conservation of momentum is that they act as a reality check against errors of this kind. In 2007, the UK Department of Trade and Industry granted SPR an export license to Boeing in the US. According to Shawyer, in December 2008 he was invited to present on the EmDrive, and in 2009 Boeing expressed interest in it, at which point he stated that SPR built

7680-463: The results in 2016 in the Journal of Propulsion and Power , under the title "Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum". The study said their system was "consistently performing with a thrust-to-power ratio of 1.2±0.1mN/kW", but also enumerated many potential sources of error. This was the first such paper published in a peer-reviewed journal, however the experiment

7776-701: The satellite. As of 2022, no launch date has yet been announced. Spacecraft propulsion Several methods of pragmatic spacecraft propulsion have been developed, each having its own drawbacks and advantages. Most satellites have simple reliable chemical thrusters (often monopropellant rockets ) or resistojet rockets for orbital station-keeping , while a few use momentum wheels for attitude control . Russian and antecedent Soviet bloc satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north–south station-keeping and orbit raising. Interplanetary vehicles mostly use chemical rockets as well, although

7872-431: The solar system is a struggle against time and distance. The most distant planets are 4.5–6 billion kilometers from the Sun and to reach them in any reasonable time requires much more capable propulsion systems than conventional chemical rockets. Rapid inner solar system missions with flexible launch dates are difficult, requiring propulsion systems that are beyond today's current state of the art. The logistics, and therefore

7968-438: The spacecraft typically moves along its trajectory without accelerating. The most fuel-efficient means to move from one circular orbit to another is with a Hohmann transfer orbit : the spacecraft begins in a roughly circular orbit around the Sun. A short period of thrust in the direction of motion accelerates or decelerates the spacecraft into an elliptical orbit around the Sun which is tangential to its previous orbit and also to

8064-445: The spacecraft's momentum. When discussing the efficiency of a propulsion system, designers often focus on the effective use of the reaction mass, which must be carried along with the rocket and is irretrievably consumed when used. Spacecraft performance can be quantified in amount of change in momentum per unit of propellant consumed, also called specific impulse . This is a measure of the amount of impulse that can be obtained from

8160-438: The spacecraft. Here other sources must provide the electrical energy (e.g. a solar panel or a nuclear reactor ), whereas the ions provide the reaction mass. The rate of change of velocity is called acceleration and the rate of change of momentum is called force . To reach a given velocity, one can apply a small acceleration over a long period of time, or a large acceleration over a short time; similarly, one can achieve

8256-466: The total system mass required to support sustained human exploration beyond Earth to destinations such as the Moon, Mars, or near-Earth objects , are daunting unless more efficient in-space propulsion technologies are developed and fielded. A variety of hypothetical propulsion techniques have been considered that require a deeper understanding of the properties of space, particularly inertial frames and

8352-438: The weight of solar panels per watt of energy supplied, at terrestrial distances from the Sun. Chemical power generators are not used due to the far lower total available energy. Beamed power to the spacecraft is considered to have potential, according to NASA and the University of Colorado Boulder . With any current source of electrical power, chemical, nuclear or solar, the maximum amount of power that can be generated limits

8448-408: The weight on Earth of the reaction mass is often unimportant when discussing vehicles in space, specific impulse can also be discussed in terms of impulse per unit mass, with the same units as velocity (e.g., meters per second). This measure is equivalent to the effective exhaust velocity of the engine, and is typically designated v e {\displaystyle v_{e}} . Either

8544-418: Was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way. A letter from physicist Paul Friedlander: As I read it, I, like the thousands of other physicists who will have read it, immediately realised that this was impossible as described. Physicists are trained to use certain fundamental principles to analyse

8640-426: Was again criticized for its small dataset and missing details about the experimental setup, which was again not independently validated. In July 2015, an aerospace research group at the Dresden University of Technology (TUD) under Martin Tajmar reported results for an evaluation of an RF resonant tapered cavity similar to the EmDrive. Testing was performed first on a knife-edge beam balance able to detect force at

8736-519: Was backed by a SMART award grant from the UK Department of Trade and Industry . In December 2002, he loosely described a prototype which he alleged had produced a thrust of 0.02 newtons (0.072  ozf ) powered by an 850 W cavity magnetron . The device could operate for only a few dozen seconds before the magnetron failed from overheating. Details were never published or replicated. In October 2006, Shawyer claimed to have conducted tests on

8832-541: Was important to use self-contained power systems for these experiments, and more sensitive pendulums with lower torsional stiffness . Since 2011, White had a team at NASA known as the Advanced Propulsion Physics Laboratory , or Eagleworks Laboratories, devoted to studying exotic propulsion concepts. The group investigated ideas for a wide range of untested and fringe proposals , including Alcubierre drives , drives that interact with

8928-505: Was measured at 91.2 μN at 17 W of input power. The experiment was criticized for its low power, small data set, and for not having been conducted in vacuum, to eliminate thermal air currents. The group announced a plan to upgrade their equipment to higher power levels, and to use a test framework subject to independent verification and validation at one or more major research centers. This did not happen. They later conducted experiments in vacuum at 40-80W of input power, publishing

9024-429: Was no evidence for any measurable thrust once these errors were taken into account. They were able to run the experiment and show no thrust in any direction, and to reintroduce the previous sources of experimental error to replicate the earlier results. They also replicated White's setup, showing that thermal effects could replicate the apparent thrust his team had observed, and that this thrust went away when measured with

9120-467: Was rotated by 90°. Moreover, they did not measure a reduction in thrust when an attenuator was used to reduce the power that actually entered the resonant cavity by a factor of 10,000, which they said "clearly indicates that the "thrust" is not coming from the EMDrive but from some electromagnetic interaction." They concluded that "magnetic interaction from not sufficiently shielded cables or thrusters are

9216-494: Was used. In an interview on CCTV in September 2017, Chen showed some testing of a flat cylindrical device, corresponding to the patent describing stacked short cavities with internal diaphragms. All proposed theories for how the EmDrive works violate the conservation of momentum , which states any interaction cannot have a net force; a consequence of the conservation of momentum is Newton's third law, where for every action there

#374625