Ryan McGlothlin takes a sugar-like powder, stirs in a substance that resembles flour, pours the mix into a mold and bakes it. The end result is not a cake but a small, shiny, black bar designed to shield against radiation. The “sugar” really is polyethylene, and the “flour” is a gray topsoil. McGlothlin, a chemistry major at the College of William and Mary, and chemistry department chairman Richard Kiefer are using those ingredients to develop a material to make bricks that would protect astronauts against radiation on Mars. They are working with aerospace researcher Sheila Thibeault at NASA Langley Research Center in nearby Hampton.