Sleeping on the trip
CONTOUR is a collaboration between NASA, Cornell University and Johns Hopkins' Applied Physics Laboratory. The relatively thrifty $150 million mission will pack a science wallop.
But first, mission planners have to get the craft headed toward an elusive target.
CONTOUR will be turned off for most of its trip out to comet Encke and spun like a discus. The dormant period is designed to save money by avoiding use of the international radio telescope network which tracks all space vehicles.
"Deep Space Network costs are not insignificant," said CONTOUR mission manager Bob Farquhar of Johns Hopkins. "They're charging for projects lately, so CONTOUR will be put in hibernation. There will be no operations, no tracking. This is a novel concept. Some people are nervous about this because we've never done this before."
While the spacecraft is napping, people will track comet Encke from the ground. About three months before the first encounter takes place, in August 2003, CONTOUR will be woken and its instruments calibrated.
Getting near the comet will not be a simple task, though. Why? Because the target is moving in more ways than one.
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| This fabric is woven from Kevlar, a synthetic fiber made of carbon. It is five times stronger than steel. Seven sheets of it, and 10 sheets of another synthetic material called Nextel will make up the spacecraft's dust shield. The shield will be all that protects CONTOUR from at least two comets' bullet-like dust. Click to enlarge.
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| This is an artist's representation of the CONTOUR spacecraft approaching a comet. The layered dust shield is facing the comet, while the instruments peek out from the sides, surrounded by solar panels. CONTOUR will hibernate for most of its 6 year mission, only to turn on for meetings with the comets, and for its Earth swing-bys. Click to enlarge.
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| The Italian spacecraft Giotto took the first picture of a nucleus of a comet on March 13, 1986. Halley's comet was found to be very porous, with most of its ice melted away. The Giotto spacecraft came within 500 miles of Halley, while CONTOUR will be getting almost 9 times closer to Encke and SW3. Click to enlarge.
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| This is the Oort Cloud, the outer limits of our solar system. Comets reside within it millions of miles apart, up to 50,000 times further away from the Sun than Earth. With a gravitational tug from the outer planets, comets can come toward the Sun, lighting up from its heat, and becoming visible on Earth. Click to enlarge.
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Schizophrenic rockets
Planets follow regular orbits around the Sun, but a comet's path is constantly rerouted by the gravitational pull of the planets and the Sun. Sometimes the pull is too much, as seen in July 1994 when comet Shoemaker-Levy 9 was swallowed by Jupiter.
And comets themselves are dynamic objects, Farquhar said.
Unlike asteroids, which are dead rocks and do not interact much with their surroundings, when comets get too close to the Sun they behave like schizophrenic rockets.
The sun's energy boils away ice and other substances from a comet, and the results are far less predictable than just a head and tail. Little-understood jets of steam and gas shoot out in all directions. The effects of these jets on a comet's path are so great that the encounters between CONTOUR and the comets could vary from initial calculations by an entire day.
To allow for the comet's unpredictability, CONTOUR has an indirect launch strategy.
Farquhar said the launch window will open in late July 2002 and will be optimal for 26 days. Once CONTOUR is launched, the craft will orbit Earth until Aug. 15 when it can be shot out into space.
Nine months later, CONTOUR will circle by Earth for a final push from our planet's gravity, and then the craft will take about three more months reach its rendezvous point.
To get as close as possible, one of the craft's cameras will begin to track the comet from a distance of 1,243 miles (2,000 kilometers), beginning about ten days before the closest encounter with the comet.
At this distance, the hurtling ice ball will look like a speck in the dark sky.
The camera acts like a homing device, steering CONTOUR on the right course even if the comet veers off its path.
Next Page: Details of the encounter and the science of CONTOUR
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