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The famed EM Drive is a bust - that's the
take-home message from a team of physicists who have tested the controversial
fuel-less propulsion system that appears to produce thrust while violating
Newton's third law. Which means physics as we know it might be safe for a
little bit longer.
Researchers from TU Dresden in Germany created
their own replica of the EM Drive and analysed the amount of force it produced
under various conditions - and found it was producing something even when
theoretically it should not. Presenting their results at this year's
Aeronautics and Astronautics Association of France's Space Propulsion
conference, the physicists admitted something was affecting the system, but it
wasn't thrust.
By hanging their replica propulsion system in
a vacuum and measuring the movement with a laser, they found they could reverse
the field, and even reduce its power - but the drive continued to behave as if
it was producing roughly the same amount of force.
This is the story of the little engine that
shouldn't – a propulsion system based on a push of electromagnetic radiation
that seems to drive forward while contradicting the very physics that explain
it.
The EM Drive is also known as a 'radio
frequency resonant cavity thruster'. Imagine a metal cone containing an
electromagnetic field that produces thrust without ejecting any material. If
you remember your high school physics, this makes no sense. At least, not
without invoking some fringe interpretations of the laws of physics.
Newton figured out that a force is a
combination of mass and acceleration. He also worked out they always come in
pairs – an action force going one way, and a reaction force going the other.
Unless some kind of mass was being pushed out
the back of this thing, an EM Drive based on a kind of propulsion simply
shouldn't move itself through empty space. But as far back as 2001, devices
based around this concept have seemed to be doing the impossible by producing a
force in a complete vacuum.
Mind you, we're not talking any serious
shoving here, with tests conducted by NASA in 2016 indicating it could barely
manage a millinewton of force. Cut an apple into a thousand blocks and then
hold one of them in your hand, and you'd get some idea of what that amount of
push would feel like.
Such a tiny effect was always in the realm of
experimental error or outside interference. Still, the distant promise of an
engine that could slowly accelerate an object towards lightspeed without
weighing it down with propellants has been too compelling to ignore.
If its effects could be scaled up, such a
system could allow us to reach nearby planets in weeks, and even distant stars
within single generations. As recently as last year there have been rumours of
research bodies carrying out tests on the device in the hope that there's been
a loophole in the laws of physics that could permit such a revolution in space
travel.
So, what's happening? There is still a mystery
to be solved, but for now it's looking as if that strange pushing motion isn't
going to prove useful for space travel.
The researchers from TU Dresden are confident
the tiny amount of force is coming from outside of the device, most likely
generated by Earth's magnetic field acting on the microwave amplifier. Any
future testing would need to shield the cabling in the device from magnetic
fields. No doubt there will be more studies in the future that will work to
resolve the question of why the EM Drive behaves as strangely as it does.
History is full of these kinds of
disappointments, where small hints of big payoffs are chased in spite of
seeming impossibility. Remember cold fusion in the 1980s?
If you're feeling disappointed, don't forget,
engineers still have a few tricks up their sleeve to achieve
fractional-lightspeed travel.
Those ideas are going to need a lot of work if
they're to be realised, but they have a lot more going for them right now than
the EM Drive; it might be time we back a different horse and let go of our
hopes for possibilities of an impossible propulsion system.
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