Plastic Spaceships

A "designer material" derived from plastic could help protect astronauts on their way to Mars.

After reading this article, you might never look at trash bags the same way again.

We all use plastic trash bags; they're so common that we hardly give them a second thought. So who would have guessed that a lowly trash bag might hold the key to sending humans to Mars?

Most household trash bags are made of a polymer called polyethylene. Variants of that molecule turn out to be excellent at shielding the most dangerous forms of space radiation. Scientists have long known this. The trouble has been trying to build a spaceship out of the flimsy stuff.

But now NASA scientists have invented a groundbreaking, polyethylene-based material called RXF1 that's even stronger and lighter than aluminium."This new material is a first in the sense that it 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.

Humans set off on a journey to Mars, an artist's concept.

To Mars in a plastic spaceship? As daft as it may sound, it could be the safest way to go.

Less is more

Protecting astronauts from deep-space radiation is a major unsolved problem. Consider a manned mission to Mars: The round-trip could last as long as 30 months, and would require leaving the protective bubble of Earth's magnetic field. 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. Secondary radiation comes from the shielding material itself. When particles of space radiation smash into atoms within the shield, they trigger tiny nuclear reactions. Those reactions produce a shower of nuclear byproducts - neutrons and other particles - that enter the spacecraft. It's a bit like trying to protect yourself from a flying bowling ball by erecting a wall of pins. You avoid the ball but get pelted by pins. "Secondaries" can be worse for astronauts' health than the original space radiation!