Space Radiation Shielding

Space radiation is comprised of atoms in which electrons have been stripped away. Ionizing radiation has so much energy it can literally knock the electrons out of any atom it strikes ionizing the atom. This can damage the atoms in human cells, leading to future health problems such as cataracts, cancer and damage to the central nervous system.

Space radiation is made up of three kinds of radiation, all representing ionizing radiation. -1- particles trapped in the Earth's magnetic field -2- particles shot into space during solar flares (solar particle events). When a solar flare or a coronal mass ejection occurs (the two often occur at the same time, but not always), large amounts of high-energy protons are released, often in the direction of the Earth. These high-energy protons can easily reach Earth in less than 30 minutes. Because such events are difficult to predict, there is often little time to prepare for their arrival. -3- galactic cosmic rays, which are high-energy protons and heavy ions from outside our solar system. Galactic cosmic rays include heavy, high-energy ions of elements that have had all their electrons stripped away as they journeyed through the galaxy at nearly the speed of light. Cosmic rays, which can cause the ionization of atoms as they pass through matter, can pass practically unimpeded through a typical spacecraft or the skin of an astronaut. Galactic cosmic rays are the dominant source of radiation that must be dealt with aboard the International Space Station, as well as on future space missions within our solar system. Because these particles are affected by the Sun's magnetic field, their average intensity is highest during the period of minimum sunspots when the Sun's magnetic field is weakest and less able to deflect them. Also, because cosmic rays are difficult to shield against and occur on each space mission, they are often more hazardous than occasional solar particle events. They are, however, easier to predict than solar particle events.

Space radiation also can produce more particles, including neutrons, when it strikes a spacecraft or an astronaut inside a spacecraft - this is called a secondary effect. Although the type of radiation is different, one mSv of space radiation is approximately equivalent to receiving three chest x rays. On Earth, we receive an average of two mSv every year from background radiation alone. Crew members could receive higher doses of space radiation during space walks. Aboard the space station, improving the amounts and types of shielding in the most frequently occupied locations, such as the sleeping quarters and the galley, has reduced the crew's exposure to space radiation.

Materials that have high hydrogen contents, such as polyethylene, can reduce primary and secondary radiation to a greater extent than metals, such as aluminum. The Radiation Shielding Program is examining new shielding materials that not only block and/or fragment more radiation than aluminum -- the material currently used to build most spacecraft structures -- but also are lighter than aluminum. Spacecraft designers have to be able to shape shielding materials to make various parts of the spacecraft. The material must protect the crew from radiation, and it must also deflect dangerous micrometeoroids. The shielding must be durable and long lasting -- able to stand up to the harsh space environment. Polyethylene is a good shielding material because it has high hydrogen content, and hydrogen atoms are good at absorbing and dispersing radiation. One development that the team is testing is reinforced polyethylene. "Since it is a ballistic shield, it also deflects micrometeorites," Kaul says. "Since it's a fabric, it can be draped around molds and shaped into specific spacecraft components." Kaul makes bricks of the material by cutting the fabric and layering 200 to 300 pieces in a brick-shaped mold in his laboratory at the Marshall center. He then uses a vacuum pump to remove air and prevent bubbles in the material, which would reduce its strength. The material is "cooked" in a special oven called an autoclave, which heats the material slowly to 200 degrees Fahrenheit while putting it under pressure of 100 pounds per square inch using nitrogen gas. The combination of heat and pressure causes the chemical reaction that bonds the layers together to form a brick weighing about half as much as a similar piece of aluminum. "Fiber is the secret of the material's strength, " explains Kaul.

If too much shielding material is used, the spacecraft becomes way too heavy to get off the ground.

Urine and Feces Bags of urine or feces is what NASA has in mind as protection for future space stations against dangerous radiation or meteorites. Space pioneers will need to recycle their urine, wastewater and feces. Lightweight filtration bags embedded in the walls of inflatable space habitats could save on launch weight costs compared to the usual life support hardware, and create a more self-sustaining existence for humans in space. http://www.technewsdaily.com/4870-space-habitats-membrane-walls-110120html.html
Polyethylene http://www.nasa.gov/about/research/radiation_shielding.html
Demron A material said to have radiation protection similar to lead shielding, while being lightweight and flexible. Three to four times more expensive than a lead apron. Proven by the United States Department of Energy to reduce high energy alpha and beta radiation, and reduce low energy gamma radiation. http://en.wikipedia.org/wiki/Demron
Gold foil The lunar modules of the Apollo program that put men on the moon were shrouded with 24 K Gold Kapton Foil. http://www.stargate-chronicles.com/web/artifacts/ , http://info.goldavenue.com/Info_site/in_glos/in_glos_foil.html