The last of five full-scale test-firings required to qualify the redesigned space shuttle booster rocket for flight has been scheduled for Aug. 18, Morton Thiokol Inc. announced Monday.

The successful test of the 126-foot-long rocket, set for 1 p.m., would clear the way for resumption of shuttle flights, grounded following the Jan. 28, 1986, Challenger disaster.A faulty seal on one of the Challenger's two boosters was blamed by a presidential commission for the explosion of the spacecraft shortly after launch. The Challenger was destroyed and its seven-member crew killed.

Morton Thiokol spokesman Rocky Raab said next week's test, which follows the successful fourth firing on June 14, will incorporate several intentional flaws to test backup systems to their limits.

"It's severely flawed. It has flaws in every joint but one. Two of the three field joints and the case-to-nozzle joint are flawed," he said.

The redesigned motor developed by Morton Thiokol to replace Challenger-era boosters incorporates new and additional O-ring seals made of cold-resistant materials, as well as improved insulation created to further reduce the possibility of super-hot gases escaping - an event blamed for the Challenger disaster.