NASA's Opportunity spacecraft made its first trajectory correction maneuver today, a scheduled operation to fine-tune its Mars-bound trajectory, or flight path.

The spacecraft and its twin, Spirit, in NASA's Mars Exploration Rover project are carrying field-geology robots for arrival at Mars in January.

For the trajectory adjustment, flight team members at NASA's Jet Propulsion Laboratory, Pasadena, Calif., commanded Opportunity to perform a prescribed sequence of thruster firings to adjust the spacecraft's flight path.

"It looks like a beautiful burn," said Jim Erickson, Mars Exploration Rover mission manager. "The thrusters fired correctly. We're on course for putting both spacecraft on Mars."

The thruster-firing sequence had three main components. First, the entire spacecraft, which is spinning at about 2 rotations per minute, turned to point its spin axis in the direction of the needed course correction. Next, thrusters that accelerate the spacecraft along the direction of that axis burned steadily for about 54 minutes. Afterwards, the spacecraft turned to its next standard cruise attitude. The attitude is changed periodically during the cruise from Earth to Mars to keep the spacecraft's antennas pointed toward Earth and its solar panels facing the Sun.

The total trajectory correction maneuver amounted to a velocity change of 16.2 meters per second (36 miles per hour) applied to Opportunity's flight path. This velocity change has two major effects. The first is to move the arrival time at Mars earlier by 1.48 days, to the intended landing date at Meridiani Planum on January 25, 2004, Universal Time (January 24, Pacific Standard Time). The second effect is to move the aimpoint at Mars from one that misses Mars by 340,000 kilometers (211,000 miles) to one that is targeted to enter the atmosphere. At launch, the spacecraft was intentionally targeted to miss Mars so that the upper stage of the Boeing Delta II launch vehicle, traveling on a nearly identical trajectory, would not hit Mars. A key purpose of today's maneuver was to adjust for that initial targeting.

As of 6 a.m. Pacific Daylight Time July 19, Opportunity will have traveled 31.5 million kilometers (19.6 million miles) since its July 7 launch. Spirit, launched on June 10, will have traveled 106.9 million kilometers (66.4 million miles). Spirit completed its first trajectory correction maneuver three weeks ago.

After arrival, the rovers will examine their landing areas for geological evidence about the history of water on Mars.

JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA's Office of Space Science, Washington, D.C.

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