Losing two satellites

While the IUS was grounded, the Shuttle continued commercial operations. STS-7 deployed another Anik C for Telesat and Palapa B1 for Indonesia, and STS-8 deployed Insat 1B for India. When STS-41B released Westar 6 for Western Union and Palapa B2 in February 1984, both of their stages

The deployment of Westar 6.
A schematic of the gimbal of the second stage of an IUS.

failed after 10 seconds. The investigation focused on the nozzles of the Star 48B motors. The fact that these were the first of a batch of five recently produced by Thiokol implied a manufacturing fault, and an examination of the remaining motors indicated that the curing of the graphite-epoxy composite wall of the nozzle had trapped bubbles of gas that had caused a burn-through when the motor fired.13

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