Morton Thiokol Inc. has delayed for a third time its final full-scale test of the redesigned space shuttle booster, saying delays in the rocket's preparation forced rescheduling of the firing to Friday.

The test, the sixth and last to formally qualify major design features of the 126-foot-long solid-fuel rocket, had initially been set for Tuesday but was first moved to Wednesday and then Thursday before the latest delays moved it to 1 p.m. MST Friday."The test is now set for Friday. There's no one main reason for that, just an accumulation of minor delays that put us back a day," said Morton Thiokol spokesman Rocky Raab.

He said he could not detail the delays, which he characterized as "just slower-than-normal progress in getting the motor ready."

Friday's test-firing will be conducted at the company's plant 25 miles west of Brigham City.

On the two earlier postponments, the company said engineers had requested more time to adequately chill the solid-fuel motor's 1.1 million pounds of propellant.