Spacecraft -Scale Magnetospheric Protection from Galactic Cosmic Radiation: NIAC Phase II Final Report

An optimal magnetic shielding configuration for significantly reducing astronaut exposure to Galactic Cosmic Radiation (GCR) on long interplanetary missions has been realized, and is referred to as the Magnetospheric Dipolar Torus (DTM). This configuration was shown to have the singular ability to deflect the vast majority of the GCR including High Z Energetic (HZE) ions. This external (to the spacecraft) dipolar field is created by an array of unidirectional toroidal High Temperature Superconductor (HTSC) windings mounted externally on the surface of the toroidally-shaped spacecraft habitat. In this way the spacecraft directly supports the magnetic hoop forces generated by the toroidal currents and thereby significantly reduces the structural mass requirements for the shield. The magnitude of the toroidal currents are arranged poloidally to flow so as to maintain the spacecraft shell as a constant flux boundary such that the magnetic flux ϕ = 0 inside the spacecraft keeping the habitat field-free with no need for providing additional coils to cancel the internal fields. As the dipole magnetic field is everywhere perpendicular to the spacecraft habitat, the DTM provides a deflecting shield to all the incoming GCR which is nearly isotropic. In addition, the DTM shields the HTSC coils as well thereby eliminating the secondary particle irradiation hazard, which can dominate over the primary GCR for shields with closed magnetic topologies. With DTM shielding it was found that both the structural and magnet mass as well as the total current requirements were significantly reduced. The DTM shielding effectiveness was calibrated in a large laboratory vacuum chamber experiment using a high energy beam as a surrogate for the GCR encountered in space. MSNW developed 3-D relativistic particle code to evaluate magnetic shielding of GCR and also employed a very accurate commercially available particle trajectory and magnetic field solver, Lorentz-3M, from Integrated Engineering to evaluate shielding effectiveness for the GCR spectrum encountered in space. The codes were employed to evaluate a wide range of magnetic topologies and shielding approaches including prior proposed magnetic shielding concepts. Four criteria for evaluation of the efficacy of magnetic shielding are discussed for three of the most developed concepts including the DTM. They are: (1) Effectiveness of the magnetic shielding using the level of protection achieved for a given magnetic geometry as a function of the magnet mass required. The DTM proved to be an order of magnitude better. (2) Issues with secondaries: The interaction of the GCR with large, exposed magnetic systems has a profound effect on the total radiation exposure inside the habitat independent of the shield effectiveness. (3) Launch and space assembly: The amount of mass, scale of structures, and complexity of assembly. (4) Advantages and other uses for the concept beyond GCR protection such as magneto-aerobraking and capture.