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SPR Ltd Experimental Thruster
SPR Ltd Experimental Thruster

Satellite Propulsion Research Ltd (SPR Ltd) a small UK based company, has demonstrated a remarkable new space propulsion technology. The company has sucessfully tested both an experimental thruster and a demonstrator engine which use patented microwave technology to convert electrical energy directly into thrust. No propellant is used in the conversion process. Thrust is produced by the amplification of the radiation pressure of an electromagnetic wave propagated through a resonant waveguide assembly.

Now Chinese researchers from Northwestern Polytechnical University (NPU) in Xi'an claim they've confirmed the theory behind this "impossible" space drive, and are proceeding to build a demonstration version. This could transform the economics of satellites, open up new possibilities for space exploration, and give the Chinese a decisive military advantage in space. [1]


Official website

How it Works

"The engineering of the Electrogravitational Drive will no doubt be the challenge of the 21st century. Progress is being made to understand the exotic physics behind the drive with all the disciplines necessary to design and engineer such a device." (EGRD)
"Take a standard copper waveguide and close off both ends. Now create microwaves using a magnetron, a device found in every microwave oven. If you inject these microwaves into the cavity, the microwaves will bounce from one end of the cavity to the other. According to the principles outlined by Maxwell, this will produce a tiny force on the end walls. Now carefully match the size of the cavity to the wavelength of the microwaves and you create a chamber in which the microwaves resonate, allowing it to store large amounts of energy.
Roger Shawyer calculates the microwaves striking the end wall at the narrow end of his cavity will transfer less momentum to the cavity than those striking the wider end." (Justin Mullins.New Science Tech)


SPR Prototype
SPR Prototype


A microwave engine, which produces high thrust, may be used to propel spacecraft where the thrust vector is at ninety degrees to the main velocity vector. It may also be used in an airborne vehicle to counteract gravitational force. The engine comprises a gimbal mounted matrix of a number of superconducting microwave thrusters 11 which are supplied with pulses of microwave energy via an array of switches 15 and enclosed in a Dewar 19 which is maintained at low temperature by liquefied gas. The engine may include an automatic control system to maintain the correct frequency of the microwave generator 7, a means 17 of dissipating the stored microwave energy, and a gyroscopic instrument 21 and motors 22,23 for maintaining the axis of thrust parallel to the direction of gravitational acceleration for an airborne vehicle.

The thruster comprises a tapered waveguide comprising a section 1, that is evacuated or filled with air, and a section 6 containing a dielectric resonator or ferrite material whose relative permeability or relative permittivity (or both) have values greater than unity. Microwaves may be introduced into the guide via a slot 2, or a probe. It is stated that the force 9, on the end wall 5, due to reflection of the microwaves, is less than the force 4, exerted on the end wall 3, thereby generating a resultant propulsive thrust. The thruster may be used to enable the orbit of a spacecraft to be maintained or changed over a period of time.

A unit which will generate thrust when provided with electrical energy at the appropriate frequency. This will enable the orbit of a spacecraft to be maintained or changed when applied over a period of time. The thrust is generated as a result of the difference in the forces obtained when electromagnetic waves are reflected at the end walls 3 and 5 of a resonant waveguide assembly. This assembly comprises an air or vacuum filled end section 1 together with a transition section 6 and an end section 8 containing an electrical material 7.

A digitally controlled beam former for a spacecraft which includes means for periodically calibrating the feed paths of the spacecraft's antenna array by measuring the apparent movement of the center of a reference signal and a nominal signal and utilising the measured data to compensate for at least the phase drift in the antenna feed paths. The measured data may also be used to compensate for amplitude and phase drift in the antenna feed paths. Drawing

Competing Technology Patents

An electromagnetic energy propulsion engine system including a hollow housing having a front part (50) and a rear end part (4) of material transparent to the passage of electromagnetic fields, electromagnetic field generating solenoidal windings (23), (25), having central axes parallel with the central axis of the engine and axially spaced from each other to provide a forward field generating winding (25) and a rear field generating winding (23), a power source (44), a control computer (42), and a power pulse generator (40) connected between the electromagnetic field generating windings and the power source and control computer. The forward field generating winding generates a rearwardly directed magnetic field toward the rear wall parallel to the central axis, and the rear field generating winding produces a forwardly directed magnetic field opposing the rearwardly directed magnetic field of the forward field generating winding so that the rearwardly directed magnetic field... Drawing

A dipolar force field propulsion system having a alternating electric field source for producing electromotive lines of force which extend in a first direction and which vary at a selected frequency and having an electric field strength of a predetermined magnitude, a source of an alternating magnetic field having magnetic lines of force which extend in a second direction which is at a predetermined angle to the first direction of the electromotive lines of force and which cross and intercept the electromotive line of force at a predetermined location defining a force field region and wherein the frequency of the alternating magnetic field substantially equal to the frequency of the alternating electric field and at a selected in phase angle therewith and wherein the magnetic field has a flux density which when multiplied times the selected frequency is less than a known characteristic field ionization potential limit; a source of neutral particles of matter having a selected... Drawing

In drive circuitry for powering an arc jet or ion engine aboard a spacecraft carrying solar panels, a start-up circuit interconnects an array of series-parallel connected solar panels to establish and maintain an arc and plasma in the engine. In the start-up circuit, an electric switch is placed in parallel with an electrode assembly of the engine. One terminal of the engine connects directly with the solar panel array, and another terminal of the engine connects via an inductor to the solar panel array. A capacitor connects across terminals of the solar panel array. A series connection of solar panels increases the voltage from that which is available from a single panel. Conduction of current from the solar panel via the inductor is initiated by the switch to store magnetic energy within the conductor. Thereupon, upon an opening of the switch, the inductor produces a relatively high voltage which strikes an arc in the engine. The voltage outputted by the solar panel array... Drawing

Research and Development


In the News

  • China Building Cylon Basestar Space Engines - The Emdrive consists of a cavity that gets flooded with microwave radiation, which theoretically will result in linear motion as supported by Einstein's ... (Gizmodo Australia, Australia - Sep 26, 2008)
  • Chinese Say They're Building 'Impossible' Space Drive - Chinese researchers claim they've confirmed the theory behind an "impossible" space drive, and are proceeding to build a demonstration version. If they're right, this might transform the economics of satellites, open up new possibilities for space exploration –- and give the Chinese a decisive military advantage in space. (Wired; Sept. 24, 2008)
  • Relativity drive: The end of wings and wheels? - Shawyer's engine, by contrast, would be propelled by microwaves generated from solar energy. The photovoltaic cells would eliminate the fuel, and with the launch weight halved, satellite manufacturers could send up two craft for the price of one, so you would only need half as many launches. (New Science Tech; Sept. 08, 2006)


Company: SPR Ltd.

Satellite Propulsion Research Ltd (SPR Ltd) was formed in October 2000 as the corporate vehicle for progressing the development of a new form of electric propulsion. This electromagnetic “EmDrive” technology provides direct conversion of electrical energy to thrust, using radiation pressure at microwave frequencies in a tapered, high Q, resonant cavity.

The first UK government funded programme was a feasibility study completed in 2002. This work confirmed the theoretical predictions in a large series of tests using an experimental thruster. In addition, the huge potential savings for the space industry were identified during the preparation of a business model.

Following an independent review of the feasibility study report, a Demonstrator programme was authorised. This covered the design, manufacture and test of an S Band Demonstrator Engine. The Engine successfully demonstrated viable performance in both Static and Dynamic test programmes, and provided the basic knowledge to design the Flight Model Thruster. Once again a full technical report was prepared and reviewed before acceptance by the UK government.

A feasibility study is currently underway to investigate second generation superconducting technology. This includes the design, build and test of an experimental thruster operating at liquid nitrogen temperature.

A flight model development programme has started on a 300W, C band thruster, specified to produce 85mN thrust.



See Discussion page


  • Why Shawyer’s ‘electromagnetic relativity drive’ is a fraud - John P. Costella wrote; "It is well known that Roger Shawyer’s ‘electromagnetic relativity drive’ violates the law of con-servation of momentum, making it simply the latest in a long line of ‘perpetuum mobiles’ that have been proposed and disproved for centuries." (4-page PDf; Oct. 5, 2006)
Roger Shawyer's reply
The momentum exchange is between the electromagnetic wave and the engine, which is attached to the spacecraft. As the engine accelerates, momentum is lost by the electromagnetic wave and gained by the spacecraft, thus satisfying the conservation of momentum. In this process, energy is lost within the resonator, thus satisfying the conservation of energy.
The emdrive concept is clearly difficult to comprehend without a rigorous study of the theory paper, which is available via or the New Scientist website. This paper, which has been subjected to a long and detailed review process by industry and government experts, derives two equations: the static thrust equation and the dynamic thrust equation.
The law of the conservation of momentum is the basis of the static thrust equation, the law of the conservation of energy is the basis of the dynamic thrust equation. Provided these two fundamental laws of physics are satisfied, there is no reason why the forces inside the resonator should sum to zero.
The equations used to calculate the guide wavelengths in the static thrust equation are very non-linear. This is exploited in the design of the resonator to maximise the ratio of end plate forces, while minimising the axial component of the side wall force. This results in a net force that produces motion in accordance with Newton’s laws.

--Penny Gruber 20:23, 29 September 2008 (PDT) AFAIK COM has to apply in any inertial frame of reference. Assuming that the microwave cavity is well sealed as it must be for the high Q's Shawyer's system needs, then no microwaves escape. The magnetron, the waveguide to the cavity, the cavity and all the waves that bounce around inside of it are intrinsically in the same frame of reference, with no ejected mass or energy other than heating from the dielectric and conduction losses of the cavity materials. The thruster ejects nothing and so by COM cannot experience any accelerating force in an external FOR.

Related Technologies

  • - Electrogravitational Singularity - The primary goal of this project is to perfect an energy flywheel system. These designs, although applicable to use as transport devices, are for ground based terrestrial operations only. By Nikolai E. Romanski




See also




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