@Tfmonkey The Van Allen Belts were shielded by gold foil. Its not a lost technology. What NASA was referring to are the heavy lift F1 rocket engines. We've since effectively solved this with Space X's Raptor Engine. The and methods of manufacture have been lost due to outsourcing and obsolescence. The US almost lost its thermonuclear arsenal because we forgot how to produce Fogbank, and only by fluke were we able to accidentally re-discover how to make it again. The government is incompetent.
@Engineer @Tfmonkey I agree with Engineer. It also depends on the type of radiation and time of exposure (total dose). The Van Allen belts are composed of charged particles (electrons and protons with few alpha particles) so even a thin foil of a highly conductive metal would have a high cross section to these types of radiation. The types of radiations that are most lethal (slow neutrons and gamma rays) would not be contained by the Earth's magnetic field.
@IcarusWax @Tfmonkey Its a really complicated subject because the government did fake many aspects of the moon landings, but they did actually go there and we know thats true because of the mirror placed on the moon. Laser measurements before the mirror was placed were all scattered and the spectrum refracted. After the laser was placed, a portion of light is reflected rather than refracted, which can only happen if there is a mirror on the moon. So then why fake it? My bets on plasma cosmology.