Changes Urged in Shuttle Part to Eliminate Erosion

Significant changes should be made before the space shuttle’s next launch to eliminate sporadic erosion in the heat-resistant material that protects the nozzle of its booster rocket, says a 240-page internal report being reviewed by the National Aeronautics and Space Administration.

The report said tests show that the material--a carbon-and-resin liner slightly more than an inch thick inside the nozzle’s aft exit cone--has on several occasions suffered “fractures . . . so numerous, so large, so closely spaced and so extensive that the integrity of the entire (cone) came into question.”

Cone Directs Exhaust

The report enumerates steps to enhance the durability of the material, which shields the cone from the hot propellant exhaust generated at launch. The cone directs exhaust and helps the rocket gain enough thrust to ensure liftoff.

Nowhere does the report describe the problem as potentially catastrophic. Top NASA officials say initial concern over the erosion has been tempered by two recent tests, which resulted in the kind of limited erosion considered normal.

But four of the six engineers who have spent hundreds of hours since August studying the erosion at the request of the rocket manufacturer, Morton Thiokol Inc., think the carbon material poses a risk of “borderline performance” and recommend that changes be made before the shuttle’s return to space, scheduled for this August.

Design Called Outdated

Two engineers dissented but one of them said the nozzle should not be used after the August flight because its design is outdated.

The material in question, carbon cloth phenolic, has been used in every shuttle flight. NASA’s concern about the material dates back to a 1983 flight, when poxlike erosion occurred in a forward section of the nozzle. NASA engineers estimated the material came within 10 seconds of burning through.

The study group’s report links the erosion to excessive water and gases trapped in the finished carbon parts. It recommends changes that include curing the material longer to reduce the moisture and gases and storing parts in humidity-controlled areas.