How Electromagnetic Propulsion Will Work

The U.S. Department of Energy (DOE) is typically not in the business of developing propulsion systems for NASA, but it is continually working on better superconducting magnets and very rapid, high-powersolid-state switches. In the mid-1990s, Goodwin chaired a session for NASA's Breakthrough Propulsion Physics Project, which is working to design propulsion systems that have no propellant, use a very high energy system and can eventually overcome inertia.

"It seemed that there should be some way to use this technology that [DOE scientists] were developing to help NASA meet their goals, and it basically sprang from that," Goodwin said. What sprang from the DOE research was Goodwin's idea for a space propulsion system that uses super-cooled, superconducting magnets vibrating 400,000 times per second. If this rapid pulse can be directed in one direction, it could create a very efficient space propulsion system with the ability to achieve speeds on the order of a fraction of 1 percent of thespeed of light.

During the first 100 nanoseconds (billionths of a second) of an electromagnet ramping up, the electromagnet is in anon-steady statethat allows it to pulse very rapidly. After it ramps up, the magnetic field reaches a steady state and no pulsing occurs. Goodwin describes the electromagnet he is using as asolenoid, which is basically a superconducting magnetic wire wrapped around a metal cylinder. The entire structure will have a diameter of 1 foot (30.5 cm), a height of 3 feet (91.4 cm) and a weight of 55.12 pounds (25 kg). The wire used for this propulsion system is aniobium-tin alloy. Several of these wire strands will be wrapped into a cable. This electromagnet is then super-cooled with liquid helium to 4 degrees Kelvin (-452.47 F / -269.15 C).

For the magnet to vibrate, you need to cause an asymmetry in the magnetic field. Goodwin plans to deliberately introduce ametal plateinto the magnetic field to enhance the vibrating movement. This plate would be made of either copper, aluminum oriron. The aluminum and copper plates are better conductors and have a greater effect on the magnetic field. The plate would be charged up and isolated from the system to create theasymmetry. Then the plate would be drained of electricity in the few microseconds (millionths of a second) before the magnet were allowed to oscillate in the opposite direction.

"Now, the catch here is, can we use this non-steady state condition in such a way that it only moves in one direction?" Goodwin said. "And that's where it's very uncertain that that can be done. That's why we would like to do an experiment to find out." Together with the cooperation ofBoeing, Goodwin is seeking funding from NASA to perform such an experiment.

The key to the system is thesolid-state switchthat would mediate the electricity being sent from the power supply to the electromagnet. This switch basically turns the electromagnet on and off 400,000 times per second. A solid-state switch looks something like an oversized computer chip -- imagine a微处理器about the size of a hockey puck. Its job is to take the steady-state power and convert it to a very rapid, high-power pulse 400,000 times per second at 30 amps and 9,000 volts.

In the next section, you'll learn where the system draws its power from and how it may send future spacecraft beyond our solar system.

The U.S. Department of Energy also is working on plans for anuclearspace reactor for NASA. Goodwin believes that this reactor could be used to power the electromagnetic-propulsion system. The DOE is working to secure funding from NASA, and a 300-kilowatt reactor could be ready by 2006. The propulsion system would be configured to convert the thermal power generated by the reactor into electric power.

"For deep space,Marsand beyond, you pretty much need to go nuclear if you are going to move any mass," Goodwin said.

The reactor will generate power through the process of inducednuclear fission, which generates energy by splittingatoms(such as uranium-235 atoms). When a single atom splits, it releases large amounts of heat andgamma radiation. One pound (0.45 kg) of highly enriched uranium, like that used to power a nuclearsubmarineor nuclear aircraft carrier, is equal to about 1 million gallons (3.8 million liters) of gasoline. One pound of uranium is only about the size of a baseball, so it could power a spacecraft for long periods of time without taking up much room on it. This kind of nuclear-powered, electromagnetically propelled spacecraft would be able to traverse incredibly large distances.

Thermal energy from a nuclear reactor could be converted into electricity to power the spacecraft.

"You couldn't make it to the nearest star, but you could look at missions to the heliopause," Goodwin said. "If it worked extremely well, it could hit speeds of a fraction of 1 percent of the speed of light. Even at that, it would take hundreds of years to reach the nearest star, which is still impractical."

Theheliopauseis the point at which the solar wind from thesunmeets the interstellar solar wind created by the otherstars. It is located about 200astronomical units(AU) from the sun (the exact location of the heliopause is unknown). One AU is equal to the average distance from the sun to the Earth, or about 93 million miles (150 million km). For comparison, Pluto is 39.53 AU from the sun.

In order to move people, a much larger device would have to be built, but the 1-foot diameter, 3-foot-tall electromagnetic could push small, unmanned spacecraft like an interstellar probe to very far distances. The system is very efficient, according to Goodwin, and it puts a lot of power through asuperconductor. The question is whether scientists can convert that power to propulsion without destroying the magnet. The rapid vibration would likely bring the magnet to the edge of its strength.

Skeptics of such a system say that all Goodwin will accomplish is to vibrate the magnet very rapidly, but it won't go anywhere. Goodwin admits that there's no evidence yet that his propulsion system will work. "It is highly speculative, and on my most wildly optimistic days, I think there's one chance in 10 that it might work," said Goodwin. Of course, 100 years ago, people believed we had even less of a chance of ever getting to space at all.