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Gravity assist to Messenger

It's easy to fly by a planet. It can be done by pointimg a spacecraft in the right direction to pass by the planet as it orbits the Sun

But inserting a craft into a planet's orbit is a different story. Too slow, the probe will drop into the planet's atmosphere and burn up. Too fast, it will fly off into space, stuck helpless in a solar orbit for billions of years.

The spacecraft head into space with all the energy and speed it had when it left the Earth, and then have to slow down to meet up with a planet.

This means it has to burn off a lot of energy during its journey. One way is to carry a large amount of fuel and perform braking maneuvers during the trip. But fuel may accounts for more than half of the spacecraft's total launch weight; adding more would weigh down the spacecraft to the point where it wouldn't be practical to launch at all.

The other technique, which MESSENGER is going to undertake on its journey to Mercury, is called "gravity assist." Most people think of speeding up a spacecraft when they hear about this concept, but it can actually work to slow one down as well.

This is due to "angular momentum," the tremendous amount of energy a planet orbiting the Sun has because of its enormous size and speed. When a spacecraft flies past that giant body, it can tap into the planet's gravity to increase its speed. When a spacecraft flies along in front of it, the opposite happens: the vehicle gives up some of its energy to the planet.

Messenger will fly by Earth, Venus and Mercury several times to burn off energy before making its final approach to the inner planet on March 18, 2011.

posted by: kyawoo at 20:18 | link | comments |
unmanned missions, space science

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