The Mars space probe "Opportunity," part of the Mars Exploration Rover mission, has faced a long journey to launch, similar to the delays experienced by the first probe "Spirit."

Spirit took off on June 10 for its 500 million kilometer (300 million mile) journey to the Red Planet, .

Opportunity was originally set for launch on June 25, but was delayed by technical problems with the cork insulation on its Delta II rocket. Another attempt was made on Saturday, but bad weather forced NASA official to postpone it again.

On Sunday, scientists found another insulation problem, just hours before lift-off.

The National Aeronautics and Space Administration had set a new launch date for Wednesday, but announced the further delay to allow more time for tests.

"A decision was made today to take additional time to perform tests on the process used to bond the cork insulation to the surface of the Delta II launch vehicle. These tests should be complete late on Wednesday," NASA spokesman George Diller said.

A band of cork about 60 centimeters (24 inches) wide is meant to insulate the rocket from the incredible heat generated by the rocket boosters. NASA is concerned that the cork insulation is not sticking to the rocket properly.

If the launch takes place Saturday, NASA has two windows of opportunity -- at 10:51 pm and 25 seconds (0251 GMT) and at 11:34 pm and five seconds-- to send the rocket off from Cape Canaveral, near the Kennedy Space Center in Florida.

NASA only has until July 15 to send Opportunity on its journey. After that date, Mars will have moved too far away for the probe to complete its trip from Earth.

Opportunity is bound for a seven-month journey through space. Its touchdown target, 491 million kilometers (305 million miles) away, is the Meridiani Planum, a zone containing a concentration of ferrous oxide situated two degrees south of Mars' equator.

Its twin Spirit is headed for the Gusev Crater, 15 degrees south of the equator of Mars.

Although both probes will set down relatively close to the Martian equator, they will be on virtually opposite sides of the planet, some 6,000 miles (9,600 kilometers) apart.

NASA is investing some 800 million dollars on two six-wheeled vehicles, which for three months are to probe sites thought to be geologically important, roaming in search of clues of how long water flowed on the Martian surface.

SPACE.WIRE