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Spacecraft to Touch Down on Asteroid


NASA is in the midst of creating a smashing finale to its wildly successful Near-Earth Asteroid Rendezvous mission (NEAR).

On Monday, spacecraft controllers at the Johns Hopkins Applied Physics Laboratory (APL), near Baltimore, Maryland, attempted to land a craft on Eros, a 21-mile-long (34 kilometer) asteroid shaped like a Dutch clog.


Scientists hope that Eros, the near-Earth asteroid that resembles a giant potato or a Dutch clog, will provide a soft landing site for the spacecraft NEAR, scheduled to land on the asteroid on February 12.
Image courtesy NASA/NEAR


The NEAR-Shoemaker probe has been orbiting Eros since Valentine's Day 2000. Though it was not designed to land on the asteroid, scientists believe there is an 85 percent chance that the craft will touchdown successfully on a six-mile wide (10 kilometer) "saddle" near the center of the asteroid.

Asteroid Observer

Over the past year, NEAR has snapped more than 160,000 photos of Eros, named after the Greek god of sexual love.

Along with the extensive photo shoot, NASA scientists have used the 1,100-pound (500 kilogram) spacecraft to measure every aspect of Eros.

NEAR has measured the asteroid's chemical composition, which is unchanged since the beginning of the universe; its gravity, which fluctuates but averages out to be about one-thousandth of Earth's gravity; and its rotation, which occurs once every five hours and 17 minutes.

Now the NEAR spacecraft is winding down its mission.

At 10:30 a.m. ET on Monday, February 12, the APL scientists sent commands to NEAR, firing its thrusters enough to slow it and lower its orbit closer to Eros.

As the craft lines up with the landing site scientists monitor its altitude and position, making corrections along the way.

The trick was that messages between Earth and NEAR take about 17 minutes to travel the 196 million miles (315 million kilometers) one way.

If one of the thruster firings fails or doesn't hit at the right time, NEAR will crash into Eros at about 20 miles (32 kilometers) an hour.

If NASA's calculations are correct, NEAR will land on the southern sunlit side at 3:00 p.m. ET, allowing the craft to continue using its solar panels for power.

While it descends, NEAR will snap photos and sent them back to Earth. These pictures are expected to be ten times more detailed than any ever taken of an asteroid.

Waiting for Signs of Life

Scientists at APL will anxiously await a signal from NEAR telling the world that it has landed safely, knowing that thousands of things could have gone wrong.

Why take the risk of ending this successful mission on a down note?

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

In other words, to the scientists at the Applied Physics Laboratory, this is a bonus round.

NEAR cannot fly back to Earth because it doesn't have enough fuel and its power will fade in time. Why not practice a once in a lifetime maneuver?

So, two days before Valentine's, Eros will lure its little satellite, NEAR, into its waiting arms. NEAR will have to perform an amazing dance to land softly on the god of love




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NEAR Facts and Figures

•  NEAR has flown as close as four kilometers (two miles) and as far away as 200 kilometers (160 miles) from the asteroid Eros to collect scientific data and take photographs.

•  NEAR had to travel nearly 2 billion miles to reach Eros.

•  Eros is made of material that has been scarcely altered since the beginning of the solar system, and probably since before the formation of the Earth.

•  Although Eros is a near-Earth asteroid, it probably spent most of its lifetime somewhere in the main belt of asteroids between Mars and Jupiter, and will spend only a brief geologic interlude—on the order of a hundred million years—close to its present orbit.