Search crews walking a grid near Hemphill, Texas, have found the shuttle Columbia's orbiter experiments recorder, or OEX, a tape recorder that stored key data about the shuttle's performance during re-entry. The recorder was found essentially intact, according to a spokeswoman for the Columbia Accident Investigation Board, but the device may have suffered heat damage and in any case, the condition of the data tape inside is not yet known.

But if data on the tape can be recovered, NASA investigators could find a gold mine of information shedding more light on the aerodynamic forces acting on the spacecraft as its flight control system struggled to keep the doomed ship on course.

"We have no way of knowing whether the data's in a condition where it can be recovered or not," said Laura Brown, a spokeswoman for the CAIB. "They suspect there may be heat damage. We just don't know what condition it might be in."

The OEX recorder was found essentially intact on the ground about seven miles from Hemphill. Seventeen years ago, divers recovered tapes from the submerged wreckage of the shuttle Challenger and managed to extract data despite extensive damage. Engineers are hopeful they can recover data from Columbia's recorders as well.

"They're taking it to JSC (Johnson Space Center) for analysis," Brown said. "They'll clean it and they're developing a testing plan for it. They want to be as careful as they can with it so they don't lose any data."

The recorder stores data on aerodynamic pressure, temperature, vibration and other variables. Only Columbia, NASA's original space shuttle, is equipped with an OEX recorder as part of a complex system used to collect data during the ship's initial test flights. The OEX recorder should not be confused with the shuttle's operational recorders, which store additional flight data as well as voice traffic from the crew's intercom. The OPS recorders have not yet been located.

Here is a bit of background on the OEX recorders from NASA's shuttle reference book.

"The support system for the orbiter experiments was developed to record data obtained and to provide time correlation for the recorded data. The information obtained through the sensors of the OEX instruments must be recorded during the orbiter mission because there is no real-time or delayed downlink of OEX data. In addition, the analog data produced by certain instruments must be digitized for recording.

"The support system for OEX comprises three subsystems: the OEX recorder, the system control module and the pulse code modulation system. The SCM is the primary interface between the OEX recorder and the experiment instruments and between the recorder and the orbiter systems. It transmits operating commands to the experiments. After such commands are transmitted, it controls the operation of the recorder to correspond to the experiment operation. The SCM is a microprocessor-based, solid-state control unit that provides a flexible means of commanding the OEX tape recorder and the OEX and modular auxiliary data system.

"The PCM system accepts both digital and analog data from the experiments. It digitizes the analog data and molds it and the digital data received directly from the experiments into a single digital data stream that is recorded on the OEX recorder. The PCM also receives time information from the orbiter timing buffer and injects it into the digital data stream to provide the required time correlation for the OEX data.

"The SCM selects any of 32 inputs and routes them to any of 28 recorder tracks or four-line driver outputs to the T-0 umbilical; executes real-time commands; controls experiments and data system components; and provides manual, semiautomatic and automatic control.

"The recorder carries 9,400 feet of magnetic tape that permits up to two hours of recording time at a tape speed of 15 inches per second. After the return of the orbiter, the data tape is played back for recording on a ground system. The tape is not usually removed from the recorder."