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74-479: The Variable Specific Impulse Magnetoplasma Rocket ( VASIMR ) is an electrothermal thruster under development for possible use in spacecraft propulsion . It uses radio waves to ionize and heat an inert propellant , forming a plasma, then a magnetic field to confine and accelerate the expanding plasma , generating thrust . It is a plasma propulsion engine , one of several types of spacecraft electric propulsion systems. The VASIMR method for heating plasma

148-432: 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

222-551: 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

296-532: 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

370-427: A comparatively poor thrust-to-weight ratio, and requires an ambient vacuum. Proposed applications for VASIMR such as the rapid transportation of people to Mars would require a very high power, low mass energy source, ten times more efficient than a nuclear reactor (see nuclear electric rocket ). In 2010 NASA Administrator Charles Bolden said that VASIMR technology could be the breakthrough technology that would reduce

444-417: 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

518-438: 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

592-807: 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 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

666-473: 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

740-560: 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

814-438: 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

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888-457: 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

962-430: 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

1036-399: A neutral gas such as argon or xenon , is injected into a hollow cylinder surfaced with electromagnets. On entering the engine, the gas is first heated to a "cold plasma" by a helicon RF antenna/coupler that bombards the gas with electromagnetic energy, at a frequency of 10 to 50 MHz , stripping electrons off the propellant atoms and producing a plasma of ions and free electrons. By varying

1110-566: 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

1184-410: 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

1258-519: 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

1332-597: 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

1406-484: 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

1480-447: Is a type of electrothermal plasma thruster/electrothermal magnetoplasma thruster. In these engines, a neutral, inert propellant is ionized and heated using radio waves. The resulting plasma is then accelerated with magnetic fields to generate thrust. Other related electrically powered spacecraft propulsion concepts are the electrodeless plasma thruster , the microwave arcjet rocket , and the pulsed inductive thruster . The propellant,

1554-462: Is being run at 100 kW for reasons that are not mentioned in the press release. In August 2019, Ad Astra announced the successful completion of tests of a new generation radio-frequency ( RF ) Power Processing Unit (PPU) for the VASIMR engine, built by Aethera Technologies Ltd. of Canada. Ad Astra declared a power of 120 kW and >97% electrical-to-RF power efficiency, and that, at 52 kg,

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1628-425: 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

1702-635: 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

1776-500: 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

1850-411: 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,

1924-424: 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

1998-462: 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

2072-561: 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

2146-463: 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

2220-518: 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

2294-727: 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

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2368-545: 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

2442-399: The magnetosphere . To counter this latter effect, two thruster units can be packaged with magnetic fields oriented in opposite directions, making a net zero-torque magnetic quadrupole . The first VASIMR experiment was conducted at Massachusetts Institute of Technology in 1983. Important refinements were introduced in the 1990s, including the use of the helicon plasma source, which replaced

2516-545: 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

2590-473: 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

2664-423: The 200 kW VX-200 engine had reached operational status. The key enabling technology, solid-state DC-RF power-processing, reached 98% efficiency. The helicon discharge used 30 kW of radio waves to turn argon gas into plasma. The remaining 170 kW of power was allocated for acceleration of plasma in the second part of the engine, via ion cyclotron resonance heating. Based on data from VX-100 testing, it

2738-502: The Ion Cyclotron Heating (ICH) section, emits electromagnetic waves in resonance with the orbits of ions and electrons as they travel through the engine. Resonance is achieved through a reduction of the magnetic field in this portion of the engine that slows the orbital motion of the plasma particles. This section further heats the plasma to greater than 1,000,000 K (1,000,000 °C; 1,800,000 °F)—about 173 times

2812-667: The VASIMR would require an electrical power level far beyond anything currently possible. On top of that, any power generation technology will produce waste heat. The necessary 200 megawatt reactor "with a power-to-mass density of 1,000 watts per kilogram " would require extremely efficient radiators to avoid the need for "football-field sized radiators". 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

2886-935: The VX-200 engine requires 200 kW electrical power to produce 5 N of thrust, or 40 kW/N. In contrast, the conventional NEXT ion thruster produces 0.327 N with only 7.7 kW, or 24 kW/N. Electrically speaking, NEXT is almost twice as efficient, and successfully completed a 48,000 hours (5.5 years) test in December 2009. New problems also emerge with VASIMR, such as interaction with strong magnetic fields and thermal management. The inefficiency with which VASIMR operates generates substantial waste heat that needs to be channeled away without creating thermal overload and thermal stress. The superconducting electromagnets necessary to contain hot plasma generate tesla -range magnetic fields that can cause problems with other onboard devices and produce unwanted torque by interaction with

2960-435: The amount of RF heating energy and plasma, VASIMR is claimed to be capable of generating either low-thrust, high–specific impulse exhaust or relatively high-thrust, low–specific impulse exhaust. The second phase of the engine is a strong solenoid-configuration electromagnet that channels the ionized plasma, acting as a convergent-divergent nozzle like the physical nozzle in conventional rocket engines. A second coupler, known as

3034-514: 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

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3108-528: 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

3182-411: The conversion of DC electric current to radio frequency power and the auxiliary equipment for the superconducting magnet. In contrast, 2009 state-of-the-art, proven ion engine designs such as NASA's High Power Electric Propulsion (HiPEP) operated at 80% total thruster/ PPU energy efficiency . On 24 October 2008, the company announced in a press release that the helicon plasma generation component of

3256-422: The design point for optimal efficiency on the VX-200 is 50 km/s exhaust velocity, or an I sp of 5000   s. The 200 kW VX-200 had executed more than 10,000 engine firings with argon propellant at full power by 2013, demonstrating greater than 70% thruster efficiency relative to RF power input. In March 2015, Ad Astra announced a $ 10 million award from NASA to advance the technology readiness of

3330-549: 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

3404-515: The electrical efficiency to be 59% based on a 90% coupling efficiency and a 65% ion speed boosting efficiency. The 100 kilowatt VASIMR experiment was successfully running by 2007 and demonstrated efficient plasma production with an ionization cost below 100   eV. VX-100 plasma output tripled the prior record of the VX-50. The VX-100 was expected to have an ion speed boosting efficiency of 80%, but could not achieve this efficiency due to losses from

3478-434: 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

3552-459: The engines, with a stated goal to reach 100   hr and 100 kW by mid-2018. In August 2017, the company reported completing its Year 2 milestones for the VASIMR electric plasma rocket engine. NASA gave approval for Ad Astra to proceed with Year 3 after reviewing completion of a 10-hour cumulative test of the VX-200SS engine at 100   kW. It appears as though the planned 200 kW design

3626-464: The first helicon plasma experiment was performed at the ASPL . VASIMR experiment 10 (VX-10) in 1998 achieved a helicon RF plasma discharge of up to 10 kW and VX-25 in 2002 of up to 25 kW. By 2005 progress at ASPL included full and efficient plasma production and acceleration of the plasma ions with the 50 kW, 0.5 newtons (0.1 lbf) thrust VX-50. Published data on the 50 kW VX-50 showed

3700-439: 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

3774-415: 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

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3848-455: 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

3922-576: The magnetic nozzle with a very narrow energy distribution, and for significantly simplified and compact magnet arrangement in the engine. VASIMR does not use electrodes; instead, it magnetically shields plasma from most hardware parts, thus eliminating electrode erosion, a major source of wear in ion engines. Compared to traditional rocket engines with very complex plumbing, high performance valves, actuators and turbopumps, VASIMR has almost no moving parts (apart from minor ones, like gas valves), maximizing long term durability. According to Ad Astra as of 2015,

3996-654: 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

4070-533: The new RF PPU is about 10x lighter than the PPUs of competing electric thrusters ( power-to-weight ratio : 2.31 kW/kg) In July 2021, Ad Astra announced the completion of a record-breaking test for the engine, running it for 28 hours at a power level of 82.5   kW. A second test, conducted from July 12 to 16, successfully ran the engine for 88 hours at a power level of 80   kW. Ad Astra anticipates conducting 100   kW power level tests in 2023. VASIMR has

4144-467: The next version of the VASIMR engine, the VX-200SS to meet the needs of deep space missions. The SS in the name stands for "steady state", as a goal of the long duration test is to demonstrate continuous operation at thermal steady state. In August 2016, Ad Astra announced completion of the milestones for the first year of its 3-year contract with NASA. This allowed for first high-power plasma firings of

4218-503: 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

4292-806: 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

4366-546: The plasma gun originally envisioned and its electrodes, adding to durability and long life. As of 2010, Ad Astra Rocket Company (AARC) was responsible for VASIMR development, signing the first Space Act Agreement on 23 June 2005 to privatize VASIMR technology. Franklin Chang Díaz is Ad Astra's chairman and CEO, and the company had a testing facility in Liberia, Costa Rica on the campus of Earth University . In 1998,

4440-542: 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

4514-420: 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

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4588-738: The remaining 40% is secondary ionizations from plasma crossing magnetic field lines and exhaust divergence. A significant portion of that 40% was waste heat (see energy conversion efficiency ). Managing and rejecting that waste heat is critical. Between April and September 2009, 200 kW tests were performed on the VX-200 prototype with 2 tesla superconducting magnets that are powered separately and not accounted for in any "efficiency" calculations. During November 2010, long duration, full power firing tests were performed, reaching steady state operation for 25 seconds and validating basic design characteristics. Results presented in January 2011 confirmed that

4662-431: 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

4736-438: 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

4810-445: 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

4884-438: 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

4958-447: The temperature of the Sun 's surface. The path of ions and electrons through the engine approximates lines parallel to the engine walls; however, the particles actually orbit those lines while traveling linearly through the engine. The final, diverging, section of the engine contains an expanding magnetic field that ejects the ions and electrons from the engine at velocities as great as 50,000 m/s (180,000 km/h). In contrast to

5032-466: 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

5106-441: The travel time on a Mars mission from 2.5 years to 5 months. However this claim has not been repeated in the last decade. In August 2008, Tim Glover, Ad Astra director of development, publicly stated that the first expected application of VASIMR engine is "hauling things [non-human cargo] from low-Earth orbit to low-lunar orbit" supporting NASA's return to Moon efforts. In order to conduct an imagined crewed trip to Mars in 39 days,

5180-456: The typical cyclotron resonance heating processes, VASIMR ions are immediately ejected from the magnetic nozzle before they achieve thermalized distribution . Based on novel theoretical work in 2004 by Alexey V. Arefiev and Boris N. Breizman of University of Texas at Austin , virtually all of the energy in the ion cyclotron wave is uniformly transferred to ionized plasma in a single-pass cyclotron absorption process. This allows for ions to leave

5254-496: 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

5328-408: 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

5402-475: Was expected that, if room temperature superconductors are ever discovered, the VX-200 engine would have a system efficiency of 60–65% and a potential thrust level of 5 N. Optimal specific impulse appeared to be around 5,000 s using low cost argon propellant. One of the remaining untested issues was whether the hot plasma actually detached from the rocket. Another issue was waste heat management. About 60% of input energy became useful kinetic energy. Much of

5476-407: Was originally developed during nuclear fusion research. VASIMR is intended to bridge the gap between high thrust, low specific impulse chemical rockets and low thrust, high specific impulse electric propulsion, but has not yet demonstrated high thrust. The VASIMR concept originated in 1977 with former NASA astronaut Franklin Chang Díaz , who has been developing the technology ever since. VASIMR

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