Researchers at NASA's Kennedy Space Center in Florida are evaluating small tiles made of space trash to find out whether they can be stored aboard spacecraft safely or even used for radiation shielding during a deep-space mission.

The circular tiles were produced at the agency's Ames Research Center in California, where engineers developed and built a compactor that melts trash but doesn't incinerate it. After compaction, a day's worth of garbage becomes an 8-inch diameter tile about half an inch thick. Plastic water bottles, clothing scraps, duct tape and foil drink pouches are left patched together in a single tile along with an amalgam of other materials left from a day of living in space.

"One of the ways these discs could be re-used is as a radiation shield because there's a lot of plastic packaging in the trash. The idea is to make these tiles, and, if the plastic components are high enough, they could actually shield radiation," said Mary Hummerick, a Qinetiq North America microbiologist at Kennedy working on the project.

Possible areas for increased radiation shielding include astronauts' sleeping quarters or perhaps a small area in the spacecraft that would be built up to serve as a storm shelter to protect crews from solar flare effects.

Hummerick and the team working in the Space Life Sciences Lab at Kennedy are trying to identify if the tiles - which are made according to recipes based on trash from shuttle missions - are free of microorganisms or at least safe enough for astronauts to come into contact with daily.

The compactor heats the trash for 3 1/2 hours to between 300 and 350 degrees F, which should be hot enough to kill any microorganisms. The mechanism also squeezes a pound of material into the compressed tile, a reduction of at least 10 times the original size.

"Hopefully we achieve sterilization within the tile," Hummerick said. "We're starting a series of tests with a certain process temperature and time. We just sent Ames six bundles of our special trash recipe. They'll compact it and send them back to us for analysis. If the time and temperature tests seem to be achieving what we want, we'll go to long-range storage testing."

The tiles are stored in an atmosphere identical to that of the International Space Station for the tests. The microbiologists take small samples from the tile and look for signs of microbial growth. They are also interested to see if the tiles will support the growth of fungi and other micro-organisms if left alone exposed in an environment like the one they would face inside a spacecraft.

"They are achieving sterilization for the most part," Hummerick said, explaining that test strips containing bacterial spores are embedded in the tiles to see if the heating and compaction process is effective in killing bacteria. "What we don't know is, can a few possible surviving bacteria go inert and then grow back."

Handling trash is an important consideration for NASA mission planners and astronauts for several reasons. First, no one wants a cramped spacecraft to become overrun with garbage. Second, resources will be extremely limited for a crew that will be expected to live in space for up to two years, the time it would take for a Mars mission.

Crews cannot simply jettison trash as they go through space because it could land on - and possible contaminate - a planet or moon. NASA policy dictates avoiding contaminating other worlds.

"We don't want to contaminate the surface of an asteroid or something just by throwing the trash out the door," said Richard Strayer, also a Kennedy-based microbiologist with Enterprise Advisory Services Inc. "If NASA doesn't do something about it, then the spacecraft will become like a landfill, with the astronauts adding trash to it every day."

Astronauts can pack their garbage from the International Space Station into Russian Progress supply ships, which burn up in Earth's atmosphere.

Another primary goal of the process is to remove water from the trash so it can be re-used by the crew. Water is one of the densest life support materials upon which astronauts depend. Because water is so dense, it is very heavy to take into space, so efficiently processing it for re-use is seen as essential to a successful mission beyond low-Earth orbit.

"The mindset is, with limited resources, whatever you can use, you want to be able to repurpose that," Hummerick said. "Water is a very valuable commodity, so you want to recover all of that you can." In addition, the very low water content after compaction makes the tiles less likely to support any microbial growth.