As NASA's Stardust comet probe barrels towards Earth for a close encounter flyby on Monday, its navigation camera appears to be working again after an apparent post-launch contamination of the device.

NASA says the loss of the camera never did threaten the well-being of the Stardust spacecraft or the main scientific mission -- capture dust particles from a comet and returning them to Earth later this decade. However, the blurred vision would reduce the accuracy of its navigation systems and scientific images as it flies by Comet Wild 2 in January of 2004.

An artist's concept of Stardust during's flyby of Earth. Photo: NASA/JPL

Engineers believe the contamination of the optical navigation camera could have occurred shortly after Stardust's launch on February 7, 1999. Hot gases coming from various spacecraft components are believed to have come in contact with the lens of the camera. The tainted navigation camera's image was blurred and dimmed because of the problem.

Ground controllers devised a plan to "boiled away" the contamination by heating the camera's instruments. This was accomplished by employing electric heaters on Stardust, using heat produced from other systems aboard the probe and utilizing heat produced by the Sun. Also, during a recent engine firing, the Sun inadvertently lit up the camera's cooling radiator, which brought the temperature even higher.

In total, the temperature of the camera's optics was increased from -31 degrees Fahrenheit to +68 degrees Fahrenheit.

After the camera was sufficiently heated, the navigation camera captured a test image of a calibration lamp located on the space probe. The lamp, which features a distinct zig-zagged pattern, was previously imaged during pre-launch activities, as well as when the camera was contaminated.

Officials say they believe that the improved images now available will insure that navigation fixes leading up to the craft's 2004 encounter with Comet Wild 2 will be accurate. Scientific images collected by Stardust's camera are also now expected to be of better quality.

NASA estimates the camera can now photograph stars two magnitudes (celestial degrees of brightness) better. The navigation camera has detected stars as faint as 9th magnitude, which should allow the spacecraft to perform its final navigation maneuvers during approach to the comet nearly at the time originally planned.

Stardust is currently due for a "sling-shot" flyby maneuver on January 15, courtesy of the natural forces of Earth's gravitational pull. Earth will give Stardust a boost into a wider orbit for its cometary voyage as the probe passes 3,700 miles above a point off the southern tip of Africa.

At 1015 GMT (5:15 a.m. EST) on Monday, the time of closest approach, Stardust will be travelling at approximately 22,400 miles per hour, or 10 kilometers per second.

Telescope owners in the western United States and the Pacific Ocean using so-called charge-coupled device detectors may be able to observe Stardust just after it passes above Earth.

About 15 hours after its closest approach to Earth, the spacecraft will pass about 61,000 miles (98,000 kilometers) from the Moon.