Comet Chaser to Swing By Earth

There's a spacecraft hot on the trail of a comet, and it's swinging by Earth for a big speed boost on Tuesday.

Rosetta will make a close approach to Earth on Nov. 13 to reach its final destination—comet 67/P Churyumov-Gerasimenko—about seven years from now.

The 3.3-ton comet chaser, launched on an Ariane 5 rocket by the European Space Agency (ESA) in 2004, will make the close encounter with the planet to pick up almost 9 percent more speed, saving it fuel and hastening its journey.

Rosetta's pass occurs around 3:57 p.m. EST (2057 GMT) and will track above the Pacific Ocean, southwest of Chile before the spacecraft flings back on course. In 2009, Rosetta is slated for another swing-by that will speed it to 86,570 mph (139,300 kph) relative to the Sun.

Swingin' by

Swing-bys take advantage of gravity to change a spacecraft?s trajectory and assist it in reaching its target. But the close encounters also soak up orbital energy: the process is like free falling toward Earth but never hitting the ground, so the gained speed isn't lost.

Rosetta's first Earth swing-by took place March 4, 2005. Tuesday's encounter will slingshot the spacecraft through the asteroid belt and enable observations of asteroid Steins, one of the mission's scientific targets.

The mission's final Earth approach, set for Nov. 13, 2009, will speed Rosetta across the asteroid belt for a second time, allow the craft's instruments to scope out asteroid Lutetia and finally push it ahead to meet up with comet 67/P Churyumov-Gerasimenko.

Once Rosetta encounters the wily comet in 2014, about 372,800,000 miles (600 million km) from the Sun, the spacecraft will eject a lander to park on the comet's surface for scientific study.

Delicate operation

Rosetta's visit to Earth this week will be poorly lit by the Sun, exposing the mission to even more blistering cold space temperatures—increasing the risk of damage to the spacecraft's sensitive electronics.

In spite of this, a few experiments both on the orbiter and its lander will be activated for calibration, scientific measurements and imaging.

Taking advantage of its 3,293-mile (5,301-kilometer) vantage point above Earth during the swing-by, Rosetta will look for shooting stars and observe the planet's atmosphere and magnetosphere.

It will also peek at urban regions in Asia, Africa and Europe, study the Moon and take a family photo of Earth and its lunar companion from a distance.

The entire operation will be controlled from ESA?s Spacecraft Operations Centre (ESOC) in Darmstadt, Germany.

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• Comets Through Time: Myth and Mystery