Nasa is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion.
British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.
According to good scientific practice, an independent third party needed to replicate Shawyer's results. As Wired.co.uk reported, this happened last year when a Chinese team built its own EmDrive and confirmed that it produced 720 mN (about 72 grams) of thrust, enough for a practical satellite thruster. Such a thruster could be powered by solar electricity, eliminating the need for the supply of propellant that occupies up to half the launch mass of many satellites. The Chinese work attracted little attention; it seems that nobody in the West believed in it.
However, a US scientist, Guido Fetta, has built his own propellant-less microwave thruster, and managed to persuade Nasa to test it out. The test results were presentedon July 30 at the 50th Joint Propulsion Conference in Cleveland, Ohio. Astonishingly enough, they are positive.
The Nasa team based at the Johnson Space Centre gave its paper the title "Anomalous Thrust Production from an RF [radio frequency] Test Device Measured on a Low-Thrust Torsion Pendulum". The five researchers spent six days setting up test equipment followed by two days of experiments with various configurations. These tests included using a "null drive" similar to the live version but modified so it would not work, and using a device which would produce the same load on the apparatus to establish whether the effect might be produced by some effect unrelated to the actual drive. They also turned the drive around the other way to check whether that had any effect.
Back in the 90s, Nasa tested what was claimed to be an antigravity device based on spinning superconducting discs. That was reported to give good test results, until researchers realised that interference from the device was affecting their measuring instruments. They have probably learned a lot since then.
The torsion balance they used to test the thrust was sensitive enough to detect a thrust of less than ten micronewtons, but the drive actually produced 30 to 50 micronewtons -- less than a thousandth of the Chinese results, but emphatically a positive result, in spite of the law of conservation of momentum:
"Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma."
This last line implies that the drive may work by pushing against the ghostly cloud of particles and anti-particles that are constantly popping into being and disappearing again in empty space. But the Nasa team has avoided trying to explain its results in favour of simply reporting what it found: "This paper will not address the physics of the quantum vacuum plasma thruster, but instead will describe the test integration, test operations, and the results obtained from the test campaign."
The drive's inventor, Guido Fetta calls it the "Cannae Drive", which he explains as a reference to the Battle of Cannae in which Hannibal decisively defeated a much stronger Roman army: you're at your best when you are in a tight corner. However, it's hard not to suspect that Star Trek's Engineer Scott -- "I cannae change the laws of physics" -- might also be an influence. (It was formerly known as the Q-Drive.)
Fetta also presented a paper at AIAA on his drive, "Numerical and Experimental Results for a Novel Propulsion Technology Requiring no On-Board Propellant". His underlying theory is very different to that of the EmDrive, but like Shawyer he has spent years trying to persuade sceptics simply to look at it. He seems to have succeeded at last.
Shawyer himself, who sent test examples of the EmDrive to the US in 2009, sees the similarity between the two.
"From what I understand of the Nasa and Cannae work -- their RF thruster actually operates along similar lines to EmDrive, except that the asymmetric force derives from a reduced reflection coefficient at one end plate," he says. He believes the design accounts for the Cannae Drive's comparatively low thrust: "Of course this degrades the Q and hence the specific thrust that can be obtained."
Fetta is working on a number of projects which he is not able to discuss at present, and Nasa's PR team was not able to get any comments from the research team. However, it's fair to assume that the results will be picked over very closely indeed, like CERN'sanomalous faster-than-light neutrinos. The neutrino issue was cleared up fairly quickly, but given that this appears to be at least the third independent propellant-less thruster to work in tests, the anomalous thrust may prove much harder to explain away.
A working microwave thruster would radically cut the cost of satellites and space stations and extend their working life, drive deep-space missions, and take astronauts to Mars in weeks rather than months. In hindsight, it may turn out to be another great British invention that someone else turned into a success.
기존의 물리학 법칙 conservation of momentum (mass가 아님.)을 깨버린
cannae drive
Physics-Defying Space Drive Confirmed by NASA, May Revolutionize Spaceflight
NASA has conducted experiments on a revolutionary space drive that seems to defy the laws of conservation of momentum and confirmed that it works.
Developed by scientist Roger Shawyer, EmDrive is a spacecraft propulsion system that allegedly creates thrust without a propellant by using electricity to direct microwaves inside a specially-designed container. If proven to be possible, such an engine would revolutionize the way we design spacecraft by eliminating the need for the huge fuel supplies that currently consist of half the launch mass of most satellites.
But here's the problem: the EmDrive seems to violate the law of conservation of momentum. A rocket accelerates forward when the fuel inside of it is shot out backwards. Momentum, a measure of mass and velocity, is exchanged between the rocket and the fuel. But where does the EmDrive's momentum come from? There are three possibilities: either the EmDrive doesn't do what its creator claims, it somehow doesn't break the law of conservation of momentum, or our fundamental understanding of classical physics is completely wrong.
Shawyer came under a lot of criticism in 2006 for his seemingly wild claims about the results of his demonstration systems. So an independent, peer-reviewed Chinese team built its own EmDrive and confirmed that it worked in papers published in 2008, 2010, and 2012. But that wasn't enough to convince skeptics, so the cavalry was brought in: NASA.
US scientist Guido Fetta built his own version of the EmDrive, called the Cannae Drive, and convinced NASA to put it to the test. On July 30, 2014, the results of the test were presented at the 50th Joint Propulsion Conference.
NASA confirmed that the drive works.
Five NASA researchers spent six days meticulously preparing the equipment and two days conducting experiments in an attempt to debunk the drive - it has happened in the past that apparent violations of the laws of physics were simply a result of interference between instruments and equipment.
But NASA confirmed that the drive generates thrust - a tiny amount, and much less than the Chinese team reported, but it nonetheless works. How? The NASA team doesn't offer an explanation in its paper.
As for why the Cannae Drive generates less thrust than the EmDrive, Shawyer believes it is a result of the design of the container in which the microwaves are directed.
Of course, the results of this experiment will come under intense scrutiny. We will have to wait a while longer before we learn whether this truly is a revolutionary drive, or simply a huge gaffe. I have my fingers crossed.
Source: Wired
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