Nasa is testing heat shields made from the soil of the Moon, Mars and rocks from asteroids.

The space agency wants to know whether the shields could withstand the intense heat and pressure placed on spacecraft when re-entering Earth's atmosphere.

The idea is that a ship could leave the Earth without a heat shield - potentially massively reducing its weight and saving it millions in fuel, or allowing it to carry more supplies.

Ahead of its return to Earth, the spacecraft would be outfitted with a shield made from resources gathered in space, or on nearby planets, and fabricated by a robot.

The idea was hit upon last year in a brainstorming session by Michael Hogue, a researcher at Nasa's Kennedy Space Center in Florida.

"Others were talking about how regolith can be used to make bricks or landing pads and I said, 'Well, if it's good for that, why can't it be used to make atmospheric entry heat shields?' " Hogue said.

A team has since been attempting to find the right mix of materials to create a shield that can withstand the heat and pressure of a journey back to Earth.

Nasa said the tests have been "very successful" so far, with small bricks of various mixtures standing up to temperatures of about 4000F.

"I expected some to fail," Hogue said. "There is an optimum range of density you need to hit for each material where it's light enough to have low enough thermal conductivity, but also structurally strong enough to survive the forces of atmospheric entry. All of our formulations that we tested with a cutting torch at least passed that."

The bricks will now be placed in front of a plasma stream in California, which will simulate the massive heat created by re-entry.