Taurus rocket on pad at Vandenberg Air Force Base, California. Photo: Orbital

In an extraordinary turn of events, a Taurus rocket has been cleared for launch on Sunday after the U.S. and Tahitian governments determined a South Pacific island isn't threatened by falling parts of the booster after all.

The Orbital Sciences-built rocket and its experimental spy satellite have been grounded for two weeks at Vandenberg Air Force Base in California. Tahitian authorities repealed a launch safety clearance on February 25 -- two days before the planned liftoff -- citing concerns the rocket's spent third stage could crash into an inhabited island.

Initially, the U.S. government said the island of concern was Maria, a tiny tropical dot in the South Pacific. The island was shown as uninhabited by Air Force maps and a United Nations database, but the Tahitian government told the U.S. two weeks ago about 200 people were now living there.

But U.S. officials on Wednesday recanted, saying Maria really is deserted and the Tahitian government was actually worried about the safety of Marutea, an atoll located northeast of Maria.

Although Marutea is populated, it is does not lie inside the predicated impact area where the rocket's third stage will fall after consuming all its solid-fuel propellant and separating from Taurus' upper stage. The so-called "drop box" is 100 miles long and 30 miles wide.

"When (engineers) compute the drop box it is really shaped like an ellipse. But to be safe, they square off the edges to make a rectangle," Air Force spokeswoman Lt. Colleen Lehne explained. "The island of concern is actually off in the corner of the rectangle and not in the ellipse."

"The Air Force and the Tahitian government have come to a mutual agreement that the flight path for the Taurus launch does not endanger any inhabited islands," Lehne said.

Asked how this dilemma was created, Lehne said: "There are a lot of little islands and there was initial confusion which island was the concern."

Maria and Marutea are just two of 118 islands and atolls that make up French Polynesia, a territory of France, that stretch along a wide area in the South Pacific Ocean.

With this peculiar problem now put to rest after two weeks and $267,000 in delay costs, liftoff has been rescheduled for the predawn hours of Sunday. The available launch window will extend from 0923-0950 GMT (4:23-4:50 a.m. EST).

Launch preparations will resume early Friday at Vandenberg's pad 576-East where the Taurus stands poised for flight. Official will convene the traditional launch readiness review meeting on Friday afternoon to issue a final "go" for liftoff.

Once launched, the Taurus will deliver the U.S. Dept. of Energy's Multispectral Thermal Imager satellite, or MTI. The craft will test new multispectral and thermal imaging technologies that could be incorporated into spy satellites of the future.

The imaging techniques could allow reconnaissance satellites to detect facilities on Earth suspected of making nuclear or chemical weapons of mass destruction.

The Air Force, which is running this launch, has until around March 18 to get the Taurus and MTI spacecraft off the ground. Otherwise, the mission likely will be delayed for at least two months to recondition batteries inside MTI.

The reconditioning will require the rocket to be "destacked" and removed from its launch pad while the batteries are refurbished.

This flight will be the fifth for Orbital's Taurus program.