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October 28, 2008

EmDrive Research

The EmDrive is highly controversial research in propulsion, which is being performed by a british inventor. It is now being funded by China, who have performed computer simulations which verify the experimental and theoretical work of the british inventor. Experiments and demonstration systems will be built over the next year which may provide more solid proof that the concept and systems will work. Critics claim that the work violates physical laws and is impossible.

An EmDrive research paper was presented at the 59th International Astronautical Congress which was held in Glasgow, Scotland, between 29 September and 3 October 2008.


A dynamic demonstrator EM drive engine was built to operate at 2.45 GHz, with a design factor of 0.844 and has a measured Q of 45,000 for an overall diameter of 280 mm. The microwave source is a water cooled magnetron with a variable output power up to a maximum of 1.2 kW. A maximum velocity of 2cm/s was achieved and a total distance of 185cm was “flown”. The direction of acceleration was opposite to the direction of thrust, thus conclusively proving that the engine obeys Newton’s laws, and that although no reaction mass is ejected, the engine is not a reactionless machine. An electrical reaction occurs between the EM wave and the reflector surfaces of the resonator, resulting in an input impedance change with acceleration. This is seen in the power curve in the figure above.



The Dynamic test rig.

China is now funding the development of the EMdrive.


The Demonstrator Engine produced a thrust of 10.4 gm against a calibrated friction torque of 7.1 gm. Input power was 421W, giving a specific thrust of 243 mN/kW.

Current Work

Current programmes include an experimental superconducting thruster. This low power, HTS (High Temperature Superconductor) device operates at liquid nitrogen temperature, and is designed for very high Q [Q is the number of reflections of the microwave bea and consequently high specific thrust. The thruster operates at 3.8 GHz, and was designed using an update of the software used for the previous S band designs. Superconducting surfaces are formed from YBCO thin films on sapphire substrates.

Small signal testing at –195 deg C has confirmed the design, with a Q of 6.8x10**6 being measured. A second programme covers the design and development of a 300 Watt C Band flight thruster. This has a specified thrust of 85 mN, and a mass of 2.92Kg. Overall dimensions are 265mm diameter at the baseplate and a height of 164mm.
The initial design of the flight thruster is complete, and a specification has been issued. Phase 1 of the thruster development has started.

Proposed EMDrive Demonstrator Satellite
A Demonstrator Satellite proposal has also been prepared, based on an existing 100 kg microsatellite design, propelled by the flight thruster. Following launch to LEO, the continuous maneuverability important for military and formation flying missions would be demonstrated. This would be followed by a spiral transfer from LEO to GEO to illustrate the large financial savings possible in communication or solar power satellite launches. Finally the spacecraft would escape Earth’s gravity and, after a total of 7 years continuous operation, reach 16.5 km/sec.

Depending on the flight path chosen, a modest science mission could be incorporated in this cruise phase.

The spacecraft would be based on a standard DMC series microsatellite. The imaging payload and propulsion system would be replaced by a C Band EmDrive engine as described in Section 8. A small science payload (<5 kg) could be carried. The total spacecraft mass would be less than 90 kg.

Assuming 100W of DC power is available to the EmDrive engine, a static thrust of 19mN would be achieved. The thrust would be continuously variable from zero to maximum by control of the input power. At the terminal velocity of 16.5 km/sec maximum thrust would be reduced to 3.5mN.

The EmDrive engine would be mounted in the payload section with the thrust vector aligned with the central axis of the spacecraft. The engine would consist of a single thruster, a fully redundant Frequency Generating Unit and two Travelling Wave Tube Amplifiers.

These units, together with isolators, combiner and cables would be mounted on a thermally radiating baseplate designed for simple integration with the spacecraft bus. All power, telemetry and command interfaces would be designed for direct compatibility with the standard spacecraft subsystems.


FURTHER READING
Superconducting radiofrequency cavities and the EMdrive

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