Artist's concept of the NEAR spacecraft orbiting Eros. Photo: JHU/APL

A NASA probe orbiting an asteroid is on track for a series of close approaches to the space rock, bringing the craft closer to asteroid Eros than ever before. NEAR Shoemaker entered orbit around Eros in February of 2000, after a four-year cruise through space.

These low passes are the last "hoorah" for the intrepid NASA probe. After the coming fly-bys are concluded, NEAR Shoemaker will be prepped for a crash-landing on Eros in mid-February, two days shy of the one year anniversary of the spacecraft entering orbit around the asteroid.

The probe fired its small thrusters on Wednesday at 1605 GMT (11:05 a.m. EST) to begin a sequence of five or six fly-bys over the next few days. The craft had been in a circular orbit 22 miles above Eros for the last six weeks as the craft conducted scientific observations.

The first low-altitude pass occurred on Wednesday shortly after the orbit-lowering maneuver. During that approach, NEAR Shoemaker came within four miles of the solar orbiting chunk of rock.

This is not a first for NEAR Shoemaker, however. The spacecraft passed only three miles from Eros in October.

"The flyovers will give us a detailed look at the surface, much like we saw when the spacecraft came within three miles of Eros during the first low flyover in October," said Dr. Andrew F. Cheng, NEAR Project Scientist at the Johns Hopkins University Applied Physics Laboratory. "This time we're going over different areas, so we can find out if the small-scale geological features we saw in the earlier images are typical of the surface."

Through Sunday morning, the craft will complete up to four more fly-bys at an altitude three to four miles each. The last fly-by in the series will come during the early hours of Sunday when the four-year old probe will fly less than two miles from the asteroid, making the event the closest view yet of an asteroid -- at least until the spacecraft deliberately flies into the asteroid on February 12.

"NEAR Shoemaker is nearly out of fuel, and by the end of January it will have completed its scientific objectives at Eros," said Dr. Robert W. Farquhar, NEAR Shoemaker Mission Director at the Applied Physics Laboratory. "The maneuvers are kind of risky, but we want to end the mission getting a lot of bonus science -- with images better than we've ever taken," he went on to describe.

After swooping down for the final pass on January 28, NEAR will swing back out to a 22-mile high circular orbit to prepare for the final "controlled descent," as NASA officials refer to it.

The landing will begin with a series of thruster firings to slowly lower the probe's orbit, before finally pushing NEAR out of orbit and toward the surface. The craft's camera will capture images of Eros at least until the spacecraft passes an altitude of 1,650 feet. The resolution of the final images could be as high as 4 inches.

In fact, the main goal of the crash-landing to capture those images.

"NEAR Shoemaker was never designed to land, so that's not the main goal of the controlled descent," explains Farquhar. "The definition of success here is getting the close-up images. We're not optimizing this maneuver to ensure the spacecraft survives this event."