The quantum vacuum plasma thruster (or Q-thruster) is a theoretical thruster that would harness quantum vacuum fluctuations to propel a spacecraft. Proponents contend that interaction with 'quantum vacuum plasma' is the cause for thrust produced by an experimental engine (abbreviated to "Q-thruster") proposed for use in deep-space propulsion. Theoretical physicists Sean M. Carroll and John Baez (see below) have dismissed this because the quantum vacuum as it is currently understood is not a plasma and does not possess any plasma-like characteristics. A research team called Eagleworks Laboratories led by Harold G. White at the NASA Johnson Space Center claims that novel physics may be responsible for the thrust observed from prototypes. No such physics has ever been claimed to have been observed by any other collaboration of physicists or engineers. If it is correct that quantum vacuum fluctuations can support thrust sufficient to propel a spacecraft, a spacecraft fitted with such a thruster would not need to carry any propellant for its operation.
Using a torsion pendulum, White's team claims to have measured approximately 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 Brady and colleagues 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. However, in early 2015, Paul March from Eagleworks 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 Brady and colleagues have never been published in a peer reviewed journal, only as a conference paper. A team of Chinese scientists have also claimed to have measured anomalous thrust arising from a similar device but have calculated anomalous thrust values on the order of 1000 times higher than those claimed by Brady and colleagues at power levels on the order of 100 times greater than that employed by Brady and colleagues.
In 2013, the Eagleworks team also tested a device called the SFE Thruster or 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. A patent for this device was awarded on December 10, 2002 to the inventor, Mr. Hector Serrano. The patent states the device produces thrust through a preselected shaping of an electric field. The device consists of a set of circular dielectrics sandwiched between electrodes. 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). To date, Eagleworks has not published a peer reviewed paper detailing the results of this experiment.
Theory of operation
The research team claims the "Q-thruster" utilizes the quantum vacuum fluctuations of empty space as a "propellant". The existence of quantum vacuum fluctuations is not disputed, because experiments with the quantum mechanical Casimir effect have unambiguously demonstrated that quantum vacuum fluctuations do exist. What remains to be proven is that these fluctuations can be utilized for this practical purpose.
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.
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.
The Q-thruster operates on the principles of magnetohydrodynamics (MHD), the same principles and equations of motion used by a conventional plasma thruster. The difference is that the Q-thruster uses the subatomic particles spontaneously produced by quantum vacuum fluctuations as its propellant. The subatomic particles are charged and are therefore effectively a plasma. This plasma is exposed to a crossed electric and magnetic field, inducing a force on the particles of the plasma in the E×B direction, which is orthogonal to the applied fields.
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.
The Q-thruster would 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 a Q-thruster need not carry any propellant. This theory suggests much higher specific impulses are available for Q-thrusters, because they only consume electrical power and thus are limited only by their power supply's energy storage densities. 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.
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.
- Dean drive
- Casimir effect
- Unruh effect
- Reactionless drive
- White–Juday warp-field interferometer—Another proposed device from the same NASA laboratory.
- Photon rocket
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