CAPE CANAVERAL, Fla. – An $85 million solar science mission is being pushed back yet another week to give engineers more time to investigate a recent Pegasus rocket failure that destroyed an experimental NASA hypersonic craft.

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Destined for launch on a similar Orbital Sciences Corp. Pegasus XL rocket, NASA’s High Energy Solar Spectroscopic Imager, or HESSI, now is expected to remain grounded until at least June 21, agency officials said Friday.

The reason: Mission managers want to make sure that the Pegasus XL rocket will not suffer the same type of airborne failure that doomed a NASA X-43 hypersonic aircraft.

"We’re still in a holding pattern," said George Diller, a spokesman for NASA’s Kennedy Space Center. "A slip of another week is anticipated."

The Pegasus XL that will be used to launch HESSI has similar systems, particularly in the first stage of the rocket. Investigators want to clear any common systems before proceeding with the HESSI launch.

The Pegasus XL and the HESSI spacecraft had been slated for launch Thursday but the mission was pushed back to June 12 at the earliest in the wake of the botched X-43 test flight.

The additional delay is intended to give an investigation team more time to ferret out the cause of the West Coast Pegasus failure.

The HESSI mission, meanwhile, is facing a deadline of sorts.

The flight batteries on its Pegasus XL launch vehicle are only certified through June 23, and if the mission is delayed beyond that date, the rocket and spacecraft might have to be flown back to Vandenberg Air Force Base in California for refurbishment.

It’s unclear how long the mission would be delayed if the Pegasus and HESSI – which arrived at Cape Canaveral earlier this month – had to be flown back to the West Coast.

The HESSI spacecraft is to be launched into a circular orbit some 373 miles (597 kilometers) above Earth.

Equipped with an imaging spectrometer, the spacecraft is designed to study solar flares, which can disrupt satellite and radio communications on Earth while triggering terrestrial power outages.

The spectrometer is expected to produce the first high-fidelity color movies of solar flares, zeroing in on high-energy X-rays and gamma rays emitted during the gigantic explosions.

Total cost of the mission – including the launch vehicle, spacecraft and three years of mission operations – will be $85 million.

HESSI originally was slated for launch last July but the mission was postponed after the spacecraft was damaged during a March 2000 vibration test at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.