Monday, March 13, 2006
NASA Mars explorer nears critical approach to Red Planet's orbit
After a seven-month voyage, the orbiter was scheduled to fire its rockets at around 2124 GMT Friday to slow the 2.2-tonne vehicle to 14,000 kilometers (8,700 miles) per hour, permitting it to be grabbed by Mars's gravitational pull.
"We have been preparing for years for the critical events the spacecraft must execute on Friday," said Jim Graf, project manager for the orbiter at the National Aeronautics and Space Administration.
"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," he told reporters at the Jet Propulsion Laboratory (JPL) in Pasadena, California. "Mars is unpredictable."
The MRO mission, "the most technologically advanced payload we have ever sent to another planet," is fraught with risks because of the difficulty of settling a craft into orbit after the lengthy journey.
The tricky part, Graf 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," Graf said.
"There is no time for the team as a whole to react, ... 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.
"For the last six minutes, we are essentially in white-knuckle time, wondering if we're going to actually complete the burn and go into orbit," said Graf.
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, or farthest point.
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.
"Our primary science phase won't begin until November, but we'll actually be studying the changeable structure of Mars's atmosphere by sensing the density of the atmosphere at different altitudes each time we fly through it during aerobraking," said JPL's Richard Zurek, project scientist for the mission.
The MRO carries six observation and analysis instruments to search for signs of water and ice from the planet's outer atmosphere to below the Martian surface.
When its 25-month research mission is over, MRO will serve as a high-speed communications relay satellite until 2011 for at least two future Mars landers.
The MRO will join two American orbiters, the Mars Global Surveyor and Mars Odyssey, and one European orbiter, Mars Express, that are already looking for signs of water and ice on the Red Planet.
NASA also has two robotic rovers, Spirit and Opportunity, on the surface of Mars.
source:http://news.yahoo.com/s/afp/20060310/ts_alt_afp/usspacemars
