July 30 2004. Copyright, 2004, Graphic News. All rights reserved

Spacecraft to begin marathon trek to Mercury

LONDON, July 30, Graphic News: 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 (700 degrees F) 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 probeÕs delicate science instruments and the blistering sun is a handmade ceramic-cloth quilt just over half a centimetre (one-quarter inch) thick.

ÒMessenger will help us understand the forces that have shaped the least explored and innermost of the terrestrial planets,Ó said Orlando Figueroa, director of the solar system exploration division at NASA. ÒUnderstanding Mercury, how it formed and how it evolved is essential to the understanding of the terrestrial planets: Venus, Earth and Mars.Ó

Mercury is an average 58 million km (36 million miles) 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 (93 million miles) from the sun and takes four times as long to circle it.

Scientists want to know how the planet turned out the way it did. In this land of extremes, the surface temperature changes a radical 550 degrees C (1,000 degrees F) from day to night, plummeting to minus-185 degrees C (minus-300 degrees F). Additionally, Mercury -- which is just a little bigger than our moon -- is about as dense as the Earth, suggesting at least two-thirds of it must be made up of iron.

Unlike Earth, Mercury does not spin on a tilted axis, which means a crater at its north or south pole would be in permanent shadow. And MercuryÕs ultra-thin atmosphere does not transport heat from the equator to the poles, as EarthÕs does.

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. The 8-billion-km (5-billion-mile) marathon will require 15 trips around the sun, six trajectory-warping flybys of Earth, Venus and Mercury, and another half-dozen critical rocket firings.

Messenger will make its first flyby of Mercury in 2008 but will not begin its main mission until 2011. The last time NASA sent a spacecraft to this planet was in 1974 and 1975, when the Mariner 10 probe made three close passes, returning detailed data on less than half of MercuryÕs surface.

By contrast, Messenger will carry seven scientific instruments, including cameras; spectrometers to figure out what chemicals are present; a magnetometer to learn more about MercuryÕs magnetic field; and an altimeter to measure its topography.

Once the $427 million (£235 million, 354 million euro) mission is accomplished in 2012, the craft will keep orbiting the scorched world until it eventually crashes onto the surface. It will go down with a pair of U.S. flags on one of its most heat-resistant surfaces -- the spacecraft team wanted to leave a flag on Mercury to show, for all time, that Americans were there first.
/ENDS

Sources: NASA, Aviation Week and Space Technology