Clearly, advances in the critical current and the transition temperature also allow significant gains to be made as well. A second required technology which must be domonstrated is the cooling of wires to the superconducting transition temperature using passive cooling, essentially shielding the wire from the sun and allowing it to radiate to deep space. An as-yet unresolved question on the use of magnetic shields involves the question of whether the field region can be allowed to penetrate into the crew area. However, considerably simpler engineering designs can be made if some magnetic field is allowed to penetrate into the shielded region. While magnetic fields in general are not hazardous to humans, it is not known what effect high steady-state magnetic fields have.
Magnetic shielding is an idea whose time has returned.
P. Birch, Radiation Shields for Ships and Settlements, J. Brit. E.C. Hannah, Radiation Protection for Space Colonies, J. British Interplanetary Soc. Space Travel for the Next Millennium, NASA CP-10059, April 1990.