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In deep space, there are very few second chances. But one year later and one year wiser, a team of Cornell University astronomers and researchers is preparing for the first spacecraft to orbit an asteroid, named 433 Eros, on Valentine's Day.

In December 1998 the NEAR (for Near Earth Asteroid Rendezvous) spacecraft almost had been given up for dead after a problem with an attempted rocket firing left the $224.1 million mission unable to complete its goal of going into orbit around asteroid Eros. But thanks to fast thinking at Cornell, NASA's Jet Propulsion Laboratory (JPL) and Johns Hopkins University's Applied Physics Laboratory (APL), which is managing the mission, signals were sent enabling the spacecraft instead to fly by 21-mile-long Eros, capturing images as it went.

Since then the spacecraft has been crawling back toward Eros (last Thursday, Feb. 3, its speed was slowed to 18 mph from 45 mph), once again preparing to enter into orbit and make the first detailed exploration of an asteroid with a full complement of instruments. By Saturday, Feb. 12 the spacecraft finally will be closer to Eros -- about 1,310 kilometers (814 miles) away -- than it was on Dec. 20, 1998, when the rocket problem occurred. At that time, the Cornell team expects to receive the highest resolution pictures of Eros yet. Cornell senior researcher Peter Thomas likens this slow yet finely detailed approach to "having to sneeze to get into orbit -- but sneezing in the right direction."

The year spent in preparing for this historical event has been well used by the mission team. Indeed, some researchers look on the unexpected months of preparation as serendipity.

"The unplanned extra year provided time to gain a lot more experience so that everyone is much more ready now than before," says Joseph Veverka, the Cornell astronomy professor who is leading the mission's science team in charge of the visible light camera and near-infrared spectrometer, two of the five science instruments carried by NEAR. His operations team also designed the spacecraft command sequences that point and operate the instruments.

For example, the unexpected images obtained in the December 1998 flyby greatly assisted in the design of commands sent to the spacecraft in recent weeks because, says Cornell researcher Colin Peterson, "we know more about the asteroid and what it looks like." Also, the flyby images helped Thomas make computer models of the asteroid's peanut shape, which the latest approach images show to be highly accurate and have helped confirm the location of Eros in the sky as seen from the spacecraft. "One of the first tests was not how good the shape model was but which way is the asteroid pointing and is it in the rotational phase we thought many months before," says Thomas. "The answer is yes, and we are much relieved to see that."

The mission team is being very cautious the second time around. In recent weeks there have been two "rehearsals" in which instructions have been sent to the spacecraft, tested and verified. On Feb. 13, 30 hours before entering orbit 200 kilometers (124 miles) above Eros, the spacecraft will perform a low-phase flyby of the asteroid. Partly this is to make sure the commands to the spacecraft are keeping it "healthy and safe," in Peterson's words, before the engine burn that will insert the spacecraft into orbit.

About 11 hours before the orbit maneuver, the spacecraft will pass directly between the asteroid and the sun at an angle that will erase shadows from Eros' surface -- as seen from NEAR. This will permit the NEAR infrared spectrometer aboard the spacecraft to measure the brightness of the surface in infrared wavelengths of light. Cornell researcher Beth Clark explains that the infrared spectroscopic observations of the asteroid's surface will tell researchers much about the minerology of Eros, helping to answer such questions as: Is Eros a rubble pile or a shard of strong material? What kinds of rock is the asteroid made of and have the rocks been changed by long exposure to space? In particular, the spectrometer will focus on the asteroid's northern hemisphere, which is currently in continual summer sunlight. This will be the only time during the mission that the spacecraft will be focused on Eros' north pole.

The spectrometer will be observing Eros at different wavelengths than can be perceived by a camera lens (or a human eye). Indeed, the imaging camera will not be able to see the surface of the asteroid during this period because the solar panels must remain in sunlight to receive power, and turning the spacecraft so that the camera could image the asteroid would result in turning the solar panels away from the sun.

At approximately 11:33 a.m. Eastern time Feb. 14, NEAR's main engine will burn to slow down the spacecraft, thrusting it into orbit around the asteroid, which is some 240 million miles from Earth. Veverka says that for the first three weeks NEAR will stay in a "loose, adjustable orbit" -- the modest mass of the asteroid means that the spacecraft will be barely bound by gravity. Eventually, he says, the orbit will settle at 200 kilometers. By April the orbit will be lowered to 100 kilometers, and by the end of May it will go into a very low 50-kilometer orbit, where it will remain for the rest of the year.

"What most of us hope," says Thomas, "is that after most of the mission's goals have been accomplished the spacecraft will go even closer, perhaps 5 kilometers (3 miles) above the surface, to obtain much higher resolution pictures." There is even a possibility, says Veverka, that next January the decision will be made to land the spacecraft on the surface of Eros.

With the orbit of Eros just a week away, the Cornell operations team remains entirely confident. "Our real apprehension came last January when the spacecraft was moving so fast, about a kilometer a second, that we had to make a big engine burn to slow it down," says Veverka. "What we have to do now is relatively easy, but we still have to make some very fine adjustments, which is a big challenge."