“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's Ames Research Center and 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.