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Five years after its launching, the probe Magellan is now approaching its fiery end when it burns up in the atmosphere of planet Earth's nearest neighbor, Venus.

Named after 16th-century Portuguese navigator Ferdinand Magellan, the space vehicle has charted 98 percent of the surface of Venus and delivered new indications about the planet's internal structure thanks to measurements taken of its gravitational fields.The sheer amount of data the probe has sent back far outnumbers the information of all of NASA's other planetary probes combined.

In a few weeks, Magellan's voyage will come to an end when it plunges into Venus' atmosphere and disintegrates.

But before the remains of the probe crash onto the planet's surface, Magellan will carry out one more experiment in aerodynamics that can help in the design of future space probes.

Starting Oct. 10, the probe's orbit around Venus will be lowered in phases, and Magellan will keep sending back data to NASA until it burns up.

It will be the end of a mission that NASA scientists say has revolutionized man's knowledge about Venus. Last year, after having concluded its cartographic work to map the planet's surface, Magellan was brought into closer orbit to measure the planet's gravitational fields.

In the process, the probe was put into an elliptical orbit in which at its lowest point the Magellan actually scraped the upper surface of the planet's atmosphere several times.

According to the magazine Space News, in being subjected to the braking effect of the atmosphere, Magellan became the first space vehicle to accomplish the maneuver without firing its retrorockets. Such maneuvers could be used in future space missions.

The Magellan was launched in May 1989 and 16 months later began orbiting Venus. Equipped with a new radar scanning system that delivered sharply focused images, the probe carried out a detailed geological survey of Venus' surface.

As the gravitational measurement operations start to come to an end, NASA is sending signals to the probe, in 102-mile orbit above Venus, to extend its two solar panels. Acting like propellor blades, the panels will change the probe's aerodynamic qualities. As the probe begins to collide with the atoms and molecules in the atmosphere, NASA scientists believe the panels will tend to move like the blades of a windmill.

NASA scientists hope the data about the probe's re-entry will shed light on the forces unleashed. To do this, they must determine how much Magellan's stabilizing system must work in order to prevent the probe from rotating.

The knowledge gained from the experiment could help in the design of future space vehicles that are suited for braking maneuvers in the atmosphere without the use of retrorockets.

The gravitational measurements are to be completed on Oct. 9, after which the probe will be lowered to an orbit of 80 miles over Venus' surface. At that point, the planet's thick cloud cover will have the Magellan firmly in its grip. What happens after that will be a matter of conjecture.