NASA prepares to feel the heat with mission to Mercury

NASA is about to embark on its hottest mission ever - to launch the first spacecraft ever to orbit Mercury, the nearest rock to the Sun.

The Messenger spacecraft, due to lift off atop a Boeing Delta 2 booster on Monday, will be baked by pizza-oven temperatures of up to 370 degrees C as it orbits the tiny planet to map its surface and look for frozen water in shady polar craters.

Remarkably, the only thing between the probe's delicate science instruments and the blistering sun is a handmade ceramic-cloth quilt just over half a centimetre (one-quarter inch) thick.

"Messenger will help us understand the forces that have shaped the least explored and innermost of the terrestrial planets," said Orlando Figueroa, director of the solar system exploration division at NASA.

"Understanding Mercury, how it formed and how it evolved is essential to the understanding of the terrestrial planets: Venus, Earth and Mars."

Mercury is an average 58 million kilometres from the sun, making for a fast elliptical loop and thus a short Mercury year of only 88 days.

Earth, by comparison, is 150 million km from the sun and takes four times as long to circle it.

In this land of extremes, the surface temperature changes a radical 550 degrees C from day to night, plummeting to minus-185 degrees C.

Taking a roundabout economy route to save the cost and weight of the extra fuel required for a quicker trip, Messenger will spend six-and-a-half years just getting to its target for one year of scientific observations.

Messenger will make its first flyby of Mercury in 2008 but will not begin its main mission until 2011.