A Boeing-built Delta II "Heavy" rocket lifted off from a launching pad at an Air Force base here at 11:18 pm (0318 GMT Tuesday), after a defective valve discovered in the first stage of the rocket postponed the launch by an hour.

A camera mounted on the rocket allowed experts to monitor the probe's nighttime ascent into the dark Florida sky.

The launch went without a hitch.

Four minutes after liftoff, Delta's main engine shut down and the first stage of the rocket separated. The engine of the second stage then took over, carrying the probe into space until it also shut down nine minutes into the flight.

Mission controllers will be able to breathe a sigh of relief only about 80 minutes into the flight, after the separation of the rocket's third stage.

At that point, Opportunity will begin its 491-million-kilometer (about 300-million-mile) journey to the Red Planet where it is expected to arrive on January 25, 2004.

Opportunity was the second of two robot probes designed to explore the planet's surface.

The spacecraft was originally set for launch June 25, but its flight has been repeatedly delayed by weather and technical problems.

The first of the twin probes, MER-A, or "Spirit," was launched on June 10, beginning a three-month, 500 million kilometer (310 million mile) voyage, intended to end on January 3, 2004 in the Gusev Crater, 15 degrees south of the equator of Mars.

The second probe is heading for the Meridiani Planum, a zone containing an concentration of ferrous oxide situated two degrees south of Mars' equator.

SPACE.WIRE