NASA Mars Explorer Set for Risky Plunge into Red Planet's Orbit

After a seven-month voyage, the orbiter was scheduled to fire its rockets at about 2124 GMT Friday to slow the 2.2 tonne vehicle to 14,000 kilometers per hour (8,700 mph) permitting it to be grabbed up by Mars' gravitational pull.

NASA artist's conception image shows the Mars Reconnaissance Orbiter (AFP Photo)

"We have a tremendous amount of anxiety and concern at this particular point in time," said Jim Graf, project manager for the Mars Reconnaissance Observer (MRO) of the National Aeronautic and Space Administration.

"It's the most technologically advanced payload we have ever sent to another planet," he said.

"At the same time we feel confident, we have a very good spacecraft ... (and an) excellent well-trained team," he said in a press conference from the Jet Propulsion Laboratory in Pasadena, California.

The MRO was sent to study the surface of Mars over 25 months by slowly descending in orbit around the planet.

The mission is fraught with risks because of the difficulty of settling a craft into orbit after the lengthy journey.

"By all indications, we're in great shape to succeed, but Mars has taught us never to get overconfident. Two of the last four orbiters NASA sent to Mars did not survive final approach," Graf said.

"Mars is unpredictable"

The tricky part, he said, will be maneuvering the craft into a Mars orbit. Because of the great distance, it takes 12 minutes for data to reach Earth from the craft, and another 12 minutes for instructions to be sent back.

So the deceleration is handled automatically by instructions programmed into the craft.

"We are about 325,000 miles (523,036 kilometers) from Mars. We're traveling at about 6,400 miles (10,300 kilometers) an hour and we are going to double our speed as we get closer to Mars," he said.

"There is no time for the team as a whole to react," he said.

"So we have on board all the programs we need to carry out, and the spacecraft has to do it all on its own."

To achieve Mars orbit, the probe's engines will begin firing at 2124 GMT on Friday for 27 minutes.

About 20 minutes later, the orbiter will disappear behind Mars for 30 minutes before it renews contact with very anxious scientists on Earth.

At first, the probe will be in a highly elliptical orbit 400 kilometers (250 miles) from Mars at the closest point and 44,000 kilometers (27,340 miles) at its apogee.

In late March, NASA engineers will start operations to bring the probe to a lower and rounder orbit to begin the 25-month observation mission.

The MRO carries six observation and analysis instruments to search from its outer atmosphere to below the Martian surface for signs of water and ice.

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