Tech Article On The Use of the OEX in 51L Investigation

Technical Article G3

The Use of Challenger's OEX Recorder in the 51L Investigation

The investigation of flight STS-107 has more than a few aspects in common with the STS-51L Challenger investigation, this section examines some of those similarities.

The OEX Data Recorder:

The STS-51L investigation used data from the Challenger's OEX recorder which was still turned on during launch and ascent even though it was the 25th shuttle mission and the flight engineers had collected all the data they needed to do structural analysis from the Columbia, (only Columbia and Challenger had OEX recorders installed. All the other shuttles were set to receive a MADS data recorder only). In the case of mission STS-51L the shuttle stack exploded approximately 73 seconds after liftoff at an altitude of 46,000 feet and a speed of Mach 1.92.

It was discovered early in the investigation by examining the launch and ascent videos that a major portion of the forward fuselage, containing the crew compartment, was still intact after the initial explosion. It was assumed that this portion of the shuttle remained intact for the 8.7 mile free-fall to the Atlantic Ocean. The OEX data recorder located in that area of the orbiter did not produce a tracking signal since it was not intended to be a post disaster data recorder but it was hoped that it might have survived the crash into the Atlantic along with other critical parts of the forward fuselage.

Luck was on the side of the recovery workers, that portion of the forward fuselage did in fact stay intact all the way to the ocean floor where the bodies of the astronauts were recovered along with the OEX data recorder. The OEX recorder was mounted in the sub-floor area of the Challengers mid deck and was therefore somewhat protected from the extreme impact with the ocean. It's also possible that the forward fuselage landed upside down with the majority of the structure absorbing the shock of impact further protecting the fragile data recorder. It must be stated that the Challengers OEX was not exposed to any reentry heating as the Columbia's would have been, to date no photos of Challengers OEX recorder after salvage retrieval have been found. A website telling how the OEX recorder was found and what the additional data meant to the investigation can be found here, What really happened to Challenger, a portion of a web page posted just below this article.

The successful salvage of the OEX data recorder from the submerged Challenger wreckage provided critical additional ascent telemetry data. This data filled remaining gaps in the accident scenario that allowed the investigative team to make the necessary conclusions and close the STS-51L investigation. It seems extraordinarily unlikely that nearly 20 years later the same lucky find of the OEX data recorder in Columbia's debris field would provide the same additional help in resolving the cause of the STS-107 accident. This is especially true considering Columbia's near complete destruction during reentry with the resulting nature of its debris being small shredded bits of shuttle components and structural materials. The only item found in Columbia's debris field almost intact and in nearly pristine condition was the OEX data recorder itself. See, Observational Analysis OA-G1; The OEX Data Recorder.

The report structure and format:

If the Rogers Report on the STS-51L Challenger incident is viewed side by side with the C.A.I.B. Final Report, it can be observed that the two reports follow an almost identical structure and format.

The main difference is that the Rogers Report contains a great deal more technical analysis than Volume I of the C.A.I.B. Final Report. There are several long sections in the STS-107 report that contain information on the history of the Space Shuttle and human space flight as well as future plans for the shuttle program and NASA. The Rogers Report focuses almost exclusively on the Challenger accident.

Debris recovery and reconstruction:

The Rogers commission was able to produce some crude but accurate data maps showing graphically where the debris that had been recovered once fit on the Challenger's fuselage. These are very similar to the more advanced E-Maps produced by the C.A.I.B.

Another aspect of the Challenger investigation similar to the Columbia is that only about 30% of the Challenger was actually recovered compared to 37% of the Columbia. This would certainly be due to the primary crash site lying deep underwater.

Challenger top side view Fig. TA-G2-1	Challenger bottom view Fig. TA-G2-2

Challenger right hand view Fig. TA-G2-3	Challenger left hand view Fig. TA-G2-4

The website presented below is the sole work of another individual and is placed here only for the convenience of the readers of Columbia's Sacrifice. Links back to the original home page are contained on the page.

WHAT REALLY HAPPENED TO CHALLENGER (Part 2)

Photo of Challenger Launch (Flawed Solid Rocket Seam Emitting Fire in NASA Photo.)

JSC Engineer Remembers Challenger Tragedy (Part 2)

by Jerry Woodfill

The Spirit of Heaviness

The heaviness descended seconds before launch. Breathing became slightly restricted with an accompanying confusion flooding my mind. It could be likened to an episode of depression and despair. At a lost for an explanation, silently, I prayed for a safe launch of Challenger. This, the 25^th journey into space for the space shuttle, was designated STS-51L. A small tape recorder in the crew compartment would collect experimental data about Challenger’s movements. As the Orbiter Experiment Data Manager, I would be responsible for having the data removed from Challenger, transported to the data lab I managed, and processed. An adjacent conference room television gave me an opportunity to view the launch. I stood among a dozen NASA employees awaiting liftoff.

Years later, I participated in a spacecraft fatality study. We determined that once every thirty-three flights there would be loss of the vehicle. The lion’s share of the fatal probability was ascribed to launch. In my view, NASA had already had two fatal missions though neither exactly fit the study criteria. The January 27^th, 1967 launch pad accident might as well have been a space fatality. It was during a plugs-out test, a simulation of space flight just days before launch. Of course, Apollo 13 was a loss as well, which, but for prayer, ingenuity, and courage should have resulted in the deaths of the crew. In respect to the chance of disaster, a space shuttle fatality was certainly a possibility. Americans had launched into space 56 times. Another disaster among the next 44 missions would yield the .033 failure estimate. Others had the view that there had yet to be a fatal manned mission. Based on their thinking, a major malfunction was long overdue.

The Explosion

Such thoughts would seem to impact the men and women who journey into space. Discussing our findings with an astronaut friend who flew four times into space, I was surprised when he agreed with the statistics. He remarked, "We know there is risk and accept it."

At 10:38 AM Central Standard Time, January 28^th, 1986, Challenger’s Solid Rocket Boosters (SRBs) ignited. The four and one half million pound shuttle system lifted heavenward on its journey. Seventy-two seconds into the flight, the television screen showed the sorrowful explosion. A Y-shaped plume of rocket exhaust smoke appeared as the NASA Public Affairs Officer voiced the words "A Major Malfunction."

The Cause?

At rest on the ocean floor among the remains of Challenger’s crew was the data recorder. It seemed fruitless to expect any part of Challenger to remain intact. The fiery explosion of tons of rocket fuel caused most to believe an instantaneous death came mercifully to the crew. Nevertheless, a very real need was apparent. Enough of Challenger must be recovered to analyze the explosion. Without sufficient evidence of cause, there could be no corrective action. For this reason, a group gathered for prayer the night following the Memorial Service. The specific petition was to recover the data recorder with a playable tape. As I joined in the prayer, the thought came, "If the recorder is found so must the crew’s bodies be recovered." The recorder was stowed in the crew compartment. While the recorder’s housing was space qualified, there was no special sealing or shock proofing for an airplane-like crash. Yet, the device was very much like a crash recorder. It would remember vehicle acceleration, velocity, and displacement during those brief 72 seconds of flight.

Orbiter Experiment Data Lab Manager (JSC 1986)

Weeks after the accident, the call came, "The OEX recorder’s data tape is ready for you." Of the four on board recorders, only the one we had prayed for initially yielded playable data. Seawater had severely degraded the remaining tapes. After signing for the tape, I brought it to the data lab and mounted the reel on the tape drive. As the spinning mechanism ascended to the prescribed speed, I watched the sync-light change from red to green. God had responded to our earlier prayer. Not only was the data recovered, its quality was among the best we had collected.

The data played out through ink-fed pens onto a strip-chart graph. The setup resembled an electrocardiogram. Each pen’s movement represented motion of Challenger. The characteristic shuttle rollover at 8 seconds was apparent. At forty seconds, I noted additional activity. This correlated with Challenger compensating for a substantial wind shear. Passing fifty seconds, all seemed serene.

At 58 seconds, I knew the lower right solid rocket booster’s lower seam opened. Of course, the crew could not have seen the extra plume of hot exhaust. Through 65 seconds, the pens remained calm distributing linear paths of ink on the chart. In a moment, I knew the burn-through would sever the right SRB’s attachment strut.

I recalled watching the scene in the conference room weeks before. At 65 seconds, all looked so perfect, so tranquil. Slowly, the pens began to oscillate as Challenger compensated for the thrust blasting from the seam’s ever growing wound. Abruptly, the gradual wavelike motion became a violent whip-like full-scale-up-down scribbling of ink. A chilling feeling swept over those watching. At 73 seconds, Challenger flat-lined. All knew - no resuscitation could restart Challenger’s electrocardiogram. (To continue click here.)

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