martes, 14 de septiembre de 2010
Space Makes Polymers Hard
Space radiation might finally be good for something. The high-energy particles that degrade spacecraft and threaten astronauts’ health could actually help make a new material useful for inflatable space habitats.
“Under space conditions, radiation is usually considered a damaging factor,” said materials physicist Alexey Kondyurin of the University of Sydney in Australia. “But in our case, space radiation plays a positive role.”
Kondyurin and colleagues developed a glue-like material that’s goopy on the ground but hardens in space, and sent it 25 miles into the stratosphere tethered to a NASA balloon. Their results are published in a report online.
Ultimately, materials like Kondyurin’s may be used to build inflatable structures in space. Lifting bulky buildings into orbit or transporting them whole to the moon or Mars is difficult and expensive. But materials that can blow up and self-harden (or “cure” in the language of materials scientists) could let future astronauts pack their houses on their backs.
“You don’t have to take it up there in the shape that you eventually want,” said University of Sydney physicist Marcela Bilek, a co-author of the new study. “You can take something in a packaged form, all folded up, and then inflate it in space and have it cure into a mechanically solid structure.”
Other groups have tested this idea with materials that harden in response to ultraviolet light. ILC Dover, a company that has built inflatable space habitat prototypes for NASA, has developed similar materials and promoted their use in solar sails, satellite antennae and sun shields for space telescopes. In a project called BIG BLUE (Baseline Inflatable-wing Glider, Balloon-Launched Unmanned Experiment), University of Kentucky undergraduates built inflatable wings for a potential Mars plane and showed that they could harden at elevations of 89,000 feet.
But the University of Sydney group was the first to investigate the effects of the electrons, ions, X-rays and gamma-rays that constantly bombard — and usually damage — structures in space.
Kondyurin and his colleagues developed several prototype materials similar to epoxy and irradiated them in ion chambers and space plasma chambers in the lab. The materials were mostly made of carbon chains that slide across each other easily, producing a soft, gel-like material. But when smacked with highly energetic particles, the chains linked up to form a more rigid structure.
To see if the same thing happened in space, the team sent 20 samples to hitch a ride on a NASA-operated balloon that carried a gamma-ray telescope called TIGRE into the stratosphere over Australia. The launch was delayed for a month due to floods, but when the skies finally cleared on April 16, 2010, the balloon took off from Alice Springs, Australia.
The team was lucky to get flight time at all, Kondyurin said. A second balloon crashed and took out a car before smacking into the ground. The third flight was canceled.
The strips of material spent three days in the stratosphere, experiencing temperature swings between -105 and 90.5 degrees Fahrenheit and pressures barely above a vacuum level.
The researchers let the material remain in its goopy phase until after it landed, and hardened it in the lab to compare it to a control material. They found that the goop that had flown in the stratosphere had more connections between its carbon chains than the Earth-bound goop.
“You get higher levels of cross-linking than what you’d get by curing on Earth,” Bilek said. “Once it comes in contact with irradiation from ions, electrons, light in space, it cures much faster.”
Different destinations, like Mars, the moon or the space station, would call for different materials, Kondyurin added. The next steps for this research “depends on space policy,” he said.
“This technology is cool and it’s interesting,” said David Cadogan, the director of research and technology at ILC Dover. But because materials that harden only in space are impossible to test on the ground, he doesn’t think the commercial spaceflight community will go for it.
“The community is very risk averse,” he said. “If they can’t put their hands on exactly what’s going to be deployed in space here on the ground, they get really nervous about using it.”
A more realistic solution for inflatable habitats, he says, are buildings that don’t need to harden at all. “Habitats just want to be a balloon,” he said. “Once you inflate it, there’s no need to have any resin on those systems to hold it together. They’re just locked in place by good design techniques.”