Quantum vacuum thruster
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A quantum vacuum plasma thruster (or Q-thruster) is a proposed type of spacecraft thruster that would work in part by acting on the virtual particles produced by quantum vacuum fluctuations. This was proposed as a possible model for an engine that could produce thrust without carrying its own propellant. Some physicists, such as Harold G. White working with microwave resonant cavity thrusters think that they might be the first examples of such an engine.
History and controversy
The name and concept is controversial. In 2008, Yu Zhu and others at China's Northwestern Polytechnical University claimed to measure thrust from such a thruster, but called it a "microwave thruster without propellant" working on quantum principles. In 2011 it was mentioned as something to be studied by Harold G. White and his team at NASA's Eagleworks Laboratories, who were working with a prototype of such a thruster. Other physicists, such as Sean M. Carroll and John Baez, dismissed it because the quantum vacuum as currently understood is not a plasma and does not possess plasma-like characteristics.
Theory of operation
A Q-thruster would use the virtual particles from quantum fluctuations of vacuum as "propellant". The existence of quantum vacuum fluctuations is not disputed, because experiments with the quantum mechanical Casimir effect have demonstrated that they exist. What remains to be proven is that these fluctuations can be stimulated and used for this purpose, or that they have properties that would allow them to be modeled by magnetohydrodynamics.
The Q-thruster might not technically be a reactionless drive, because it expels the plasma and thus produces force on the spacecraft in the opposite direction, like a conventional rocket engine. However, a spacecraft using one need not carry any propellant. As with other plasma engines, high specific impulses would be available for Q-thrusters. Preliminary analyses suggest thrust levels of between 1000–4000 μN, a specific force performance of 0.1 N/kW, and an equivalent specific impulse of ~1x1012 s.
Controversy and criticism
A number of notable physicists have found the Q-thruster concept to be implausible. For example, mathematical physicist John Baez has criticized the reference to "quantum vacuum virtual plasma" noting that: "There's no such thing as 'virtual plasma' ". Noted Caltech theoretical physicist Sean M. Carroll has also affirmed this statement, writing "[t]here is no such thing as a ‘quantum vacuum virtual plasma,’...". In addition, Lafleur found that quantum field theory predicts no net force, implying that the measured thrusts are unlikely to be due to quantum effects. However, Lafleur noted that this conclusion was based on the assumption that the electric and magnetic fields were homogeneous, whereas certain theories posit a small net force in inhomogeneous vacuums.
Especially, the violation of energy and momentum conservation laws have been heavily criticized. In a presentation at Nasa Ames Research Centre in November, 2014, Harold White addressed the issue of conservation of momentum by stating that the Q-thruster conserves momentum by creating a wake or anisotropic state in the quantum vacuum. White indicated that once false positives were ruled out, Eagleworks would explore the momentum distribution and divergence angle of the quantum vacuum wake using a second Q-thruster to measure the quantum vacuum wake. In a paper published in January, 2014, White proposed to address the conservation of momentum issue by stating that the Q-thruster pushes quantum particles (electrons/positrons) in one direction, whereas the Q-thruster recoils to conserve momentum in the other direction. White stated that this principle was similar to how a submarine uses its propeller to push water in one direction, while the submarine recoils to conserve momentum. Hence, the violations of fundamental laws of physics can be avoided.
Other hypothesized quantum vacuum thrusters
A number of physicists have suggested that a spacecraft or object may generate thrust through its interaction with the quantum vacuum. For example, Fabrizio Pinto in a 2006 paper published in the Journal of the British Interplanetary Society noted it may be possible to bring a cluster of polarisable vacuum particles to a hover in the laboratory and then to transfer thrust to a macroscopic accelerating vehicle. Similarly, Jordan Maclay in a 2004 paper titled "A Gedanken Spacecraft that Operates Using the Quantum Vacuum (Dynamic Casimir Effect)" published in the scientific journal Foundations of Physics noted that it is possible to accelerate a spacecraft based on the dynamic Casimir effect, in which electromagnetic radiation is emitted when an uncharged mirror is properly accelerated in vacuum. Similarly, Puthoff noted in a 2010 paper titled "Engineering the Zero-Point Field and Polarizable Vacuum For Interstellar Flight" published in the Journal of the British Interplanetary Society noted that it may be possible that the quantum vacuum might be manipulated so as to provide energy/thrust for future space vehicles. Likewise, researcher Yoshinari Minami in a 2008 paper titled "Preliminary Theoretical Considerations for Getting Thrust via Squeezed Vacuum" published in the Journal of the British Interplanetary Society noted the theoretical possibility of extracting thrust from the excited vacuum induced by controlling squeezed light. In addition, Alexander Feigel in a 2009 paper noted that propulsion in quantum vacuum may be achieved by rotating or aggregating magneto-electric nano-particles in strong perpendicular electrical and magnetic fields. Likewise, Luigi Maxmilian Caligiuri in a 2014 paper published in the journal Astrophysics and Space Science noted the possibility of a space propulsion system using the interaction between the zero-point field of the quantum vacuum and the high-potential electric field generated in an asymmetrical capacitor, showing the resulting force would be driven by quantum vacuum energy density.
However, according to Puthoff, although this method can produce angular momentum causing a static disk (known as a Feynman disk) to begin to rotate, it cannot induce linear momentum due to a phenomenon known as "hidden momentum" that cancels the ability of the proposed E×B propulsion method to generate linear momentum. However, some recent experimental and theoretical work by van Tiggelen and colleagues suggests that linear momentum may be transferred from the quantum vacuum in the presence of an external magnetic field.
In 2013, the Eagleworks team tested a device called the Serrano Field Effect Thruster, built by Gravitec Inc. at the request of Boeing and DARPA. The Eagleworks team has theorized that this device is a Q-thruster. The thruster consists of a set of circular dielectrics sandwiched between electrodes; its inventor describes it device as producing thrust through a preselected shaping of an electric field. Gravitec Inc. alleges that in 2011 they tested the "asymmetrical capacitor" device in a high vacuum several times and have ruled out ion wind or electrostatic forces as an explanation for the thrust produced. In February through June 2013, the Eagleworks team evaluated the SFE test article in and out of a Faraday Shield and at various vacuum conditions. Thrust was observed in the ~1–20 N/kW range. The magnitude of the thrust scaled approximately with the cube of the input voltage (20–110 μN). As of 2015, the researchers have not published a peer reviewed paper detailing the results of this experiment.
Using a torsion pendulum, White's team claimed to have measured 30–50 μN of thrust from a microwave cavity resonator designed by Guido Fetta in an attempt at propellant-less propulsion. Using the same measurement equipment, a non-zero force was also measured on a "null" resonator that was not designed to experience any such force, which they suggest hints at "interaction with the quantum vacuum virtual plasma". All measurements were performed at atmospheric pressure, presumably in contact with air, and with no analysis of systematic errors, except for the use of an RF load without the resonant cavity interior as a control device. In early 2015, Paul March from that team made new results public, claiming positive experimental force measurements with a torsional pendulum in a hard vacuum: about 50 µN with 50 W of input power at 5.0×10−6 torr, and new null-thrust tests. The claims of the team have not yet been published in a peer reviewed journal, only as a conference paper in 2013.
Yu Zhu previously claimed to have measured anomalous thrust arising from a similar device, using power levels roughly 100 times greater, and measuring thrust roughly 1000 times greater.
As of 2015, Eagleworks is attempting to gather performance data to support development of a Q-thruster engineering prototype for reaction-control-system applications in the force range of 0.1–1 N with a corresponding input electrical power range of 0.3–3 kW. The group plans to begin by testing a refurbished test article to improve the historical performance of a 2006 experiment that attempted to demonstrate the Woodward effect. The photograph shows the test article and the plot diagram shows the thrust trace from a 500g load cell in experiments performed in 2006.
The group hopes that testing the device on a high-fidelity torsion pendulum (1–4 μN at 10–40 W) will unambiguously demonstrate the feasibility of this concept. The team is maintaining a dialogue with the ISS national labs office for an on-orbit detailed test objective (DTO) to test the Q-thruster's operation in the vacuum and weightlessness of outer space.
- Reactionless drive
- RF resonant cavity thruster (EmDrive, Cannae drive)
- White–Juday warp-field interferometer — A device used to test such drives
- Dean drive
- Casimir effect
- Unruh effect
- Photon rocket
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