For decades, the only means of space travel have been rocket engines that run off of chemical propulsion. Now, at the beginning of the 21st century, aerospace engineers are devising innovative ways to take us to the stars, including light propulsion, nuclear-fusion propulsion and antimatter propulsion. A new type of spacecraft that lacks any propellant is also being proposed. This type of spacecraft, which would be jolted through space by electromagnets, could take us farther than any of these other methods.
When cooled to extremely low temperatures, electromagnets demonstrate an unusual behavior: For the first few nanoseconds after electricity is applied to them, they vibrate. David Goodwin, a program manager at the U.S. Department of Energy's Office of High Energy and Nuclear Physics, proposes that if this vibration can be contained in one direction, it could provide enough of a jolt to send spacecraft farther and faster into space than any other propulsion method in development.
Goodwin was invited to present his idea at a Joint Propulsion Conference on July 8, 2001, in Salt Lake City, Utah. In this edition of How Stuff Will Work, you will get to see just how Goodwin's electromagnetic propulsion system works and how it could send spacecraft deep into space.
Jolting Into Space
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-power solid-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 the speed of light.
During the first 100 nanoseconds (billionths of a second) of an electromagnet ramping up, the electromagnet is in a non-steady state that 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 a solenoid, 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 a niobium-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 a metal plate into the magnetic field to enhance the vibrating movement. This plate would be made of either copper, aluminum or iron. 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 the asymmetry. 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 of Boeing, Goodwin is seeking funding from NASA to perform such an experiment.
The key to the system is the solid-state switch that 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 microprocessor 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.
Beyond Our Solar System
The U.S. Department of Energy also is working on plans for a nuclear space 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, Mars and 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 induced nuclear fission, which generates energy by splitting atoms (such as uranium-235 atoms). When a single atom splits, it releases large amounts of heat and gamma radiation. One pound (0.45 kg) of highly enriched uranium, like that used to power a nuclear submarine or 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.
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Thermal energy from a nuclear reactor could be converted into electricity to power the spacecraft. Here we see a uranium-235 nucleus splitting through induced fission.
"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."
The heliopause is the point at which the solar wind from the sun meets the interstellar solar wind created by the other stars. It is located about 200 astronomical 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 a superconductor. 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.