A JUDDERING magnet has inspired a scientist at the US Department of Energy to
investigate a bizarre new way of propelling a spacecraft.
The idea for a 鈥渏udder-drive鈥� struck David Goodwin when he noticed that
powerful cryogenically cooled superconducting magnets often jolt in one
direction for a centimetre or two when you first turn them on.
鈥淚f you have something metal in the magnetic field as it is forming, you see
the magnet physically shift,鈥� Goodwin, who works at the Office of High Energy
and Nuclear Physics in Germantown, Maryland, told 快猫短视频.
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Superconducting magnets are cooled to such a low temperature that they have
no electrical resistance. Goodwin鈥檚 magnets were made by taking superconducting
wires of niobium-tin alloy and twisting the strands into a cable. The cables
were then coated with an insulator and wound into a coil. 鈥淭he coil鈥檚 then put
into a cylindrical casing called a cryostat that鈥檚 filled with liquid helium,鈥�
says Goodwin. The liquid helium cools the wire coil to 鈭�269 掳C, when they
become superconducting.
Goodwin says the metal objects create the judder effect by inducing a 鈥渂rief
asymmetry in the magnetic field鈥� as it is set up when the magnet is turned on.
This initial disturbance of the magnetic field, he says, creates a repulsive
force on the magnet and pushes it away.
But the force produced in one jolt is very low, Goodwin says, so you would
need to turn the magnet on and off with ultrafast switches, making a fast stream
of jolts. 鈥淲e鈥檝e got switches now that can work at high voltages at 400,000
times a second,鈥� he says. 鈥淚f you could use one of these switches to rapidly
switch the magnet on and off, you might get some propulsion out of it.鈥�
A colleague of Goodwin鈥檚 at Brookhaven National Laboratory in New York is now
modelling the magnetic field of superconducting magnets to work out how best to
arrange a metallic disc in the magnetic field to produce the biggest jolt. But
Goodwin admits the judder drive might be going nowhere fast. 鈥淚t鈥檚 very
speculative. We don鈥檛 know if it鈥檒l work,鈥� he says.
Marc Millis, who heads NASA鈥檚 breakthrough propulsion physics project at the
NASA Glenn Research Center at Lewis Field in Cleveland, Ohio, has invited
Goodwin to present his idea at a propulsion conference in July next year.
The crucial thing, says Millis, is whether Goodwin鈥檚 magnet would produce any
net motion at all鈥攊t might just sit there and vibrate. 鈥淚t鈥檚 a definite
possibility that any forces arising from Goodwin鈥檚 concept will only act within
the components of the device itself, resulting in no net force,鈥� he says. 鈥淭here
are a lot of unresolved physics issues to address.鈥�