October 29, 2009

EMDrive Progress

The Emdrive Programme – Implications for the Future of the Aerospace Industry - R Shawyer, Satellite Propulsion Research Ltd was presented in the Space Technologies track of the CEAS 2009 European Air & Space Conference.

UPDATE: A link to the 14 page word document on the 2009 EMDrive research

Wired has details on the EMDrive presentation.

The heart of the Emdrive is a resonant, tapered cavity filled with microwaves. According to Shawyer, a relativistic effect generates a net thrust, an effect confirmed by various Emdrives he has built as demonstrations. Critics say that any thrust from the drive must come from another source. Shawyer is adamant that the measured thrust is not caused by other factors.

Last year, professor Yang Juan of the College of Astronautics at Northwestern Polytechnical University (NPU) in Xi’an was happy to confirm that they were building an Emdrive which would be tested by the end of the year. But following the publication of this news in Danger Room, the situation changed. I was informed that the publicity was very unwelcome, especially any suggestion that there might be a military application. (Yang had previous published a study on the use of plasma as a weapon against low-orbiting satellites. [.pdf]) No further information has been forthcoming, and no Chinese papers have been published on the Emdrive, though Yang has recently published work on (unrelated) microwave plasma thrusters (.pdf).

Shawyer asserts that work is also being carried out in France, Russia and in the United States by a major aerospace company. But he cannot provide details beyond vague promises of “significant progress [that] has been made in both theoretical and experimental work, within these groups.” He also asserts that the British National Space Centre is said to be reviewing the Emdrive.

Previous thrusters generated relatively modest forces; the latest version now being built is based on a cooled superconductor and should generate more than 300 pounds of thrust for a 6-kilowatt input, Shawyer promises. (But does not yet appear to have done so.) The plan is to mount four of these thrusters on an unmanned demonstration vehicle that will weigh about 1,000 pounds. The craft will have no wings: It will be supported by the Emdrives and propelled by jet engines to about 230 knots. It will be capable of vertical takeoff and hovering silently in place. If successful, it will be adapted as a personal transport -– your very own flying car.

In the longer run, perhaps 10 years, Shawyer envisages a hybrid spaceplane using Emdrive technology — see the photo above of a 2-meter scale model. The idea is a craft capable of making the 10,000-mile run from London to Sydney, Australia in under three hours … or taking a 40-ton payload on the moon in about four days.

The EMdrive enables superconducting cavities to very efficiently create static thrust. Thrust is measured in "pounds of thrust" in the U.S. and in Newtons under the metric system (4.45 Newtons of thrust equals 1 pound of thrust). 300 pounds of thrust is 1335 Newtons of thrust. 6 kilowatts of input means that 222.5 N/kW.

Apparently the 6.8 million Q device has 143 kg opf thrust from 6 kW input.

Effect of increased Q for the Emdrive

Q=50,000 (1st gen.) Static thrust=315 mN/kW Specific thrust at 3km/s=200mN/kW

Q=6,800,000 (supercond) Static thrust=222 N/kW Specific thrust at ??km/s=??N/kW

Q=5* 10**9 (supercond) Static thrust=31.5 kN/kW Specific thrust at 0.1km/s=8.8N/kW

Q=10**11 (supercond) Static thrust=630 kN/kW Specific thrust at 0.1km/s=??N/kW

Very high Q superconducting cavities would allow more static lift. Making multi-billion Q factor cavities and working EMdrive would enable cloud cities and long duration/near permanent flying platforms for antennas, weapons and other purposes.

High Power Density Power Sources

Very high power to weight ratio could be used to power station keeping in space or even provide the equivalent of antigravity. There are ultrathin solar arrays.

Current results of 5,880 Watts per kilogram at 7-9 micron polymer.

16,800 Watts kilogram for 2 micron thickness polymer at 168 Watt/m2
AMO Standard 1357 W/m2 @ +90°C, 12.4% efficient, a-Si:H cells.
Power density over 10,000 Watts per kg for European Sail Tower SPS Concept.
a-Si:H cells on 2 micron NASA CP1 or M-SRS CORIN Polyimide

A proposed and in development Hyperion Power Generation uranium hydride reactor should weight 15-20 tons to generate 27-30 MWe. 0.5 - 0.75 tons per MWe. (1.5 to 2 KWe per Kg). There needs to be a light weight converter of heat to electricity. Supercritical CO2 turbines could be very small and relatively light.

Superconducting Cavities if EMDrive Works

Operating at temperatures just above absolute zero, superconducting cavities accelerate bunches of electrons and positrons toward the detectors in a proposed international linear collider. Nine smooth cells, polished in all possible ways. Made of the purest niobium. Not a speck of dust or the slightest difference in shape. Superconducting when supercold Photo: Fermilab

Superconducting cavities are a key component of an enhanced version of the controversial Emdrive [electromagnetic drive].

Prototype C-band emdrive (The emdrive has been funded by China and could be a breakthrough in space and terrestrial propulsion or it is a one to two million dollar scientific mistake.) [by the cinderblock in the background it appears to be less one foot tall]

Effect of increased Q for the Emdrive

Q=50,000 (1st gen.) Static thrust=315 mN/kW Specific thrust at 3km/s=200mN/kW

Q=6,800,000 (supercond) Static thrust=42.8 N/kW Specific thrust at ??km/s=??N/kW

Q=5* 10**9 (supercond) Static thrust=31.5 kN/kW Specific thrust at 0.1km/s=8.8N/kW

Q=10**11 (supercond) Static thrust=630 kN/kW Specific thrust at 0.1km/s=??N/kW

SPR ltd is working on a superconducting demo which should be 100 times more powerful than the first version and provide 30 newtons of force instead of 315 milli-newtons. China is also building a large S-band thruster.

Superconducting radiofrequency (SCRF) cavities are also the main technology for a new international linear collider.

The main vehicle for SCRF technology is the cavity, a hollow structure that drives particles to higher energies. For the ILC, we will use roughly 16,000 metre-long nine-cell 1.3 GHz (gigahertz) niobium cavities. So far ILC scientists have achieved the target gradient goal in roughly a dozen cavities. “We have proven that the technology works,” says Cornell University’s Hasan Padamsee. “Now we need to improve the yield.” In some cases, ILC cavities have actually exceeded the
target goal and reached a gradient of 40 MV/m. Consistently reaching a gradient of 35 MV/m, however, in a large number of cavities remains a problem.

The European Commission has accepted to fund the ILC-HiGrade, or “International Linear Collider and High Gradient Superconducting RF-Cavities,” proposal within its Seventh Framework Programme (FP7) with five million Euros over the next four years. Under this contract, at least 24 superconducting cavities will be created to demonstrate the gradient feasibility for the ILC.

This kind of superconductivity cavity would be one thousand to twenty thousand times better than the crude superconducting demo that SPR ltd currently has. A very good nobium cavity could probably be created for $400,000 to 800,000 [converting the Euro price to dollars and increasing the cost for one instead of 24].

A 2002 study of superconducting cavity costs worked out to $100,000 per meter.

In the same 2002 presentation by Pierre Bauer, it appears that the maximum Q value is at least higher than 100 billion for certain kinds of nobium cooled to about 1 degree kelvin.

Possible research for higher Q cavities [2002 list]:
1) cavity manufacturing (“seam-less” techniques such as hydro-forming,…)
2) materials – e.g. replacing bulk Nb with Nb on Cu
3) surface resistance – e.g. understanding the surface chemistry that leads to low surface resistance, exploring materials which produce lower surface resistance,..etc
4) Higher gradients in view of a second stage in the same tunnel – e.g. pushing Nb to the absolute limit, exploring other materials such as Nb3Sn and NbN;

This dynamic test rig moved at 2 cm per second using the first generation emdrive. If the crude superconducting test system can be made to work then it should move the a heavier (ten tons instead of 100kg) dynamic test rig at 2 cm per second [the system loses energy with more speed].

A couple million dollars of equipment and labor at risk over two years to verify what could be a huge multi-trillion dollar breakthrough or a fairly cheap mistake (or something inbetween).

Superconducting Radio Frequency at wikipedia

It is commonplace for a 1.3 GHz niobium SRF resonant cavity at 1.8 Kelvin to obtain Q=5×10**10 [50 billion]. Such a very high Q resonator and its narrow bandwidth can then be exploited for a variety of applications. At present, none of the "high Tc" superconducting materials are suited for RF applications. Shortcomings of these materials arise due to their underlying physics as well as their bulk mechanical properties not being amenable to fabricating accelerator cavities.

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