Plastic spaceships?

NASA scientists have invented a new polyethylene-based material called RXF1 that's even stronger and lighter than aluminium and could be used to shield spacecraft from deep-space radiation.

"This new material combines superior structural properties with superior shielding properties," says Nasser Barghouty, Project Scientist for NASA's Space Radiation Shielding Project at the Marshall Space Flight Center.

Protecting astronauts from deep-space radiation is a major problem. Some scientists believe that materials such as aluminium, which provide adequate shielding in Earth orbit or for short trips to the Moon, would be inadequate for the trip to Mars.

Barghouty is one of the skeptics: "Going to Mars now with an aluminium spaceship is undoable," he believes.

Plastic is an appealing alternative: Compared to aluminium, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.

The advantage of plastic-like materials is that they produce far less "secondary radiation" than heavier materials like aluminium or lead.

Ironically, heavier elements like lead, which people often assume to be the best radiation shielding, produce much more secondary radiation than lighter elements like carbon and hydrogen.

That's why polyethylene makes good shielding: it is composed entirely of lightweight carbon and hydrogen atoms, which minimizes secondaries.

The RXF1 polyethylene material the researchers have come up with is remarkably strong and light: it has 3 times the tensile strength of aluminium, yet is 2.6 times lighter --impressive even by aerospace standards.

Since it is a ballistic shield, it also deflects micrometeorites. And since it's a fabric, it can be draped around moulds and shaped into specific spacecraft components.

But it’s not all good news for the new material. Strength is only one of the traits that the walls of a spaceship must have. Flammability and temperature tolerance are also important. And pure polyethylene is very flammable and more work is needed to customize RXF1 even further to make it flame and temperature resistant as well.

At present, the specifics of how RXF1 is made are secret because a patent on the material is pending.