Astronauts on deep-space missions may one day deploy protective magnetic fields similar to those that shelter us from deadly space radiation on Earth, just as they will carry the necessary food and atmosphere.
and its industrial and academic partners are studying ways to use superconducting magnets to generate magnetic fields around deep-space habitats. A promising approach would use coils that “inflate” with their own magnetism to deflect solar-flare protons and galactic cosmic rays that otherwise would restrict human travel time in space.
“The concept of shielding astronauts with magnetic fields has been studied for over 40 years, and it remains an intractable engineering problem,” says Shayne Westover of(JSC). “Superconducting magnet technology has made great strides in the past decade.”
Westover is principal investigator on aInnovative Advanced Concepts (NIAC) grant to study high-temperature superconductor technology as an approach to active radiation shielding for astronauts. Under the grant, JSC is working with a company that has expertise in superconducting magnets to gain some definition on just how effective they can be in protecting spaceflight crews.
“Radiation shielding, if it is not at the top of the list, is No. 2,” says Palm Bay, Fla.-based Advanced Magnet Lab President Mark Senti. “They have propulsion figured out, and I'm not trivializing anything. They have solar protection and energy, but if you don't solve radiation shielding, there's no sense in doing engineering everywhere else.”
That was essentially the conclusion of the panel headed by formerCEO Norman Augustine that studied the future of human spaceflight, at the beginning of President Barack Obama's first term. Since then, NASA has increased its focus on “enabling technology” for deep-space human exploration. The two-year, $500,000 NIAC grant headed by Westover is examining an AML concept that would launch superconducting-magnet coils and then expand them to provide the diameter necessary to produce enough magnetic shielding to protect a crew.
AML Chief Scientist Rainer Meinke conceived of attaching superconducting magnetic tape to a flexible material such as Kevlar. The perpendicular expansion provided by the Lorentz force when current is passed through the tape opens it from a collapsed configuration maintained during launch into large coils that can encircle a habitat. The current concept would launch six collapsed coils and the habitat separately, and then set up the active shielding in space (see illustration).
“In a superconducting magnet, because you're able to transmit electricity with zero resistance, [you can] pass very high currents, which means very strong magnetic fields,” Senti says.
AML plans to conduct a subscale demonstration of the coil expansion at the National High Magnetic Field Laboratory in Tallahassee, Fla. However, most of the work under the NIAC grant will be analytical. Westover and his colleagues at JSC, AML, NASA'sand Italy's University of Perugia plan to move beyond the Phase 1 concept definition already funded into more detailed engineering.
Among the issues to be considered, says Westover, is gaining a “total spacecraft” understanding of the radiation dose a crew would receive inside the magnetic shield surrounding a 6-meter-dia. X 10-meter-long (19.6 X 32.8-ft.) cylindrical habitat. Because the shielding does not cover the cylinder's end caps, Westover and his team will calculate the passive shielding that would be provided at one end by a propulsion module and at the other, by a docking mechanism for the planned Orion multipurpose crew vehicle. Scientists in Perugia will conduct Monte Carlo simulations of radiation traces through the notional hab, which will include a compensation coil to protect crew and electronics from prolonged exposure to the strong magnetic “fringe fields” that would otherwise enter the living space.
Also on the agenda is a search for ways to expand manufacture of superconducting magnetic tape from hundreds of meters to the “kilometers” that would be needed in the concept. While the tape exerts almost zero resistance on an electrical current—allowing it to maintain its magnetic field with only a “trickle current” from the habitat's solar arrays—splices in the tape add resistance and increase power requirements, says Westover.
For years, engineers also have studied toroidal coils as a way to shield space habitats. But the structure needed to hold the magnets in place—and the power necessary to produce a magnetic field strong enough to protect the crew—creates “very large forces on the hab.” In concept at least, that problem would be mitigated by the expandable-coil approach. The NIAC study should help refine the understanding of just how much better that setup will be at lowering the lifetime radiation doses for deep-space crews.
As a practical matter, the shielding can be expressed as the number of space launches needed to deliver enough of it to protect a crew for a mission lasting a year or more. Compared to passive shielding, the effectiveness of active shielding “might be as high as two to five launches,” Westover says.