Engineers Never Had Seen Such Badly Damaged Tapes as Those From Challenger With PM-Challenger Tapes Bjt

WASHINGTON (AP) _ NASA engineers said they had never seen tapes so badly damaged as the ones salvaged from the ocean floor with the crew cabin of the space shuttle Challenger, but the space agency says a four-month effort recovered at least some of the information the recordings contained.

International Business Machines Corp. developed a cleaning process which restored the tapes to playable condition.

Engineers worked initially on a payload recorder tape because it was the lowest priority of the five damaged tapes.

''We didn't want to start with a high priority tape in case something went wrong,'' said Joe Melugin, an engineer at the Johnson Space Center in Houston who worked on the restoration effort. ''We were exploring new ground. We haven't found anyone who has played a tape as badly damaged as this one.''

The tapes were recovered from the Atlantic about six weeks after the Challenger blew apart 73 seconds after its Jan. 28 launch from Cape Canaveral, Fla. All seven astronauts were killed.

The National Aeronautics and Space Administration released no information from the tapes on Thursday, but said preliminary analysis indicated the crew did not know the shuttle was in trouble moments before the explosion.

The tape ended at the same time ground communication with the Challenger stopped, NASA said.

When the tape restoration process began, the tapes used to record flight data and voice communications among the astronauts were so severely damaged by the salt water, ''I wouldn't have given you a plug nickel for them,'' Joe Mechelay, manager of the flight evaluation office at Johnson Space Center, said last month in an interview.

The damage was caused mainly by the reaction of the tape recorders' magnesium reels with the salt water, engineers said. Five tapes were damaged by the chemical reaction - two that recorded flight data and voice communications, two with computer data and one with payload data.

The cleaning process, which began at the Marshall Space Flight Center in Huntsville, Ala., involved flushing the tapes with a solution to fix the binder holding the magnetic particles containing the recorded information to the plastic base of the tape. The tape was then unwound and copied onto another tape for playback analysis, engineers said.

Tapes from another recorder, a Modular Auxiliary Data System which recorded ''developmental'' data such as stresses and vibrations of the orbiter, were not damaged as badly because their reels were made of aluminum, NASA officials said.

Most of the information on those tapes was recovered, but it offered no new insight into the explosion, NASA said.