Subject: Re: Richard Feynman explains why Mars a one way trip
You can get protection from cosmic rays by being deep underground, but we don't know how to generate gravity under those conditions. These are not "we don't know how" like we didn't know how to develop velcro before we did it - these are "we don't know how" in the sense that nothing we know about the physics of the material world suggests a possible solution at current levels of knowledge about the universe.

Passive (dead mass weight) is not the only method that can block cosmic rays. They can be deflected with magnetic fields in the same manner that the Earth does it. We just need a large source of power. Advances in fusion that will hopefully occur over the next decade or two could provide the needed power generation, and until then, the risk can be mitigated by shorter trips and stays as long as there are humans willing to put themselves at risk. At least, this is my optimistic - perhaps rose-colored glasses level - outlook.

There are many methods of blocking space radiation. They include active and passive methods of radiation shielding. Active methods of space radiation shielding employ electric and magnetic fields to deflect the charged particles away from the crew volume before interacting with the spacecraft material. The result is very similar to the protection we enjoy due to Earth’s magnetic bubble.

Theoretically, active shielding is the best possible solution since it reduces the likelihood of secondary particle generation. However, the application of active shielding in space-like conditions is challenging from an engineering point of view: the amount of electric and magnetic fields required to deflect highly energetic charged particles is in the range of hundreds of megavolts.

Although some advanced research is ongoing to reduce the requirements for such fields to be effective, active shielding is not yet a reality, leaving us with passive shielding for now.

See https://stemrad.com/blocking-s...

There's also talk of "radiation vests" - AstroRad - there that use special materials. See https://stemrad.com/astrorad-4...

The shielding itself in the AstroRad is comprised of a polymer with a high abundance of hydrogen which is advantageous for shielding against space radiation because it minimizes the generation of secondary radiation. Individual solid shielding elements are organized into a scale-like architecture to allow for uninhibited, comfortable movement of the astronauts while wearing the AstroRad. StemRad is currently exploring the use of recycled plastics materials generated onboard future spacecraft for use in the shielding elements which would dramatically decrease the payload mass associated with the equipment.