A. Introduction/Summary

The SRM Recovery Support Team reviewed video film, sketches, and photographs taken of the various SRM fragments on the ocean for, and after recovery, to identify structural pieces (fragments) of the Solid Rocket Boosters (SRBs). Primary emphasis was placed on identifying those structural pieces of the right SRB at the aft to aft center field joint area. Although recovery survey operations continue, one significant portion of the right aft center segment has been recovered. This fragment spans approximately 178 degrees with a section of the tang and case wall of approximately 400 square inches missing from 294 to 316 degrees. The edges of this "hole" show the effects of high heating and melting indicative of a burn through. A significant portion of the aft segment was recovered April 28, 1986. This fragment spans approximately 94° at station 1577.48 and approximately 38° at the ET attach stubs. A section of the clevis and case wall of approximately 425 square inches is missing from 291° to 318°. The SRM case material adjacent to the burn through and below the clevis was fractured. The clevis in this area has not been located.

In the course of the recovery operations many pieces of hardware were recovered which were not relative to the STS 51-L incident. These pieces include:

Two other structural pieces of the right aft center segment have been schematically oriented but are not from the joint of interest.

Eight structural pieces of the right aft segment have been schematically oriented. Of the eight, two pieces are from the joint area of interest.

Two structural pieces from the right forward center segment and one from the forward segment have been schematically oriented.

Seven structural pieces of the right SRB aft skirt have been schematically oriented.

Five structural pieces of the left SRB were schematically oriented.

B. Organization/Responsibilities

The SRM Recovery Support Team was established to support the SRM Working Group and indirectly support the Salvage Support Team (Figure A-1). The Team involved MSFC and Contractor personnel knowledgeable in the hardware elements and structural components of the SRB and SRM which comprise the SRB.

The Team is composed of the following members:

Additional support personnel produced weight analyses and graphics.

The primary responsibility of the Team was to review all available data to aid in the identification of the SRB debris. The Team assisted in establishing priority for recovery of the debris in an effort to determine the cause of the STS 51-L incident.

The principal data reviewed included the underwater video and photographs from search and recovery ships, the underwater sonar contact plots, radar and photographic reconstruction of SRB fragment trajectories from command destruct to water impact, engineering documentation and STS 51-L build history.

C. Method of Investigation

Using visual recordings of SRB fragments supplied to the SRM Recovery Support Team by KSC, the visual characteristics were analyzed and categorized to allow plotting on a schematic layout. Those fragments deemed to be of importance to the investigation were prioritized for recovery by the salvage vessels. The assets provided the research materials. The identifying characteristics were applied to each piece to provide a means for schematic orientation.

Assets:

• Underwater video tape
• Underwater still photographs
• Artist renditions of underwater artifacts
• Radar trajectory plots
• Sonar cross-reference charts
• NASA Select Press Briefing video tape
• Land-based photographs of recovered hardware
• Assembly blueprints
• Propellant burnback pattern charts
• Assembly closeout photographs

Identifying Characteristics:

• Inherently unique pieces
• Bolt hole sizes (ET attach ring)
• Pin hole sizes (clevis)
• Proximity of known (identified) pieces to adjacent (unidentified) pieces
• Pin and bolt hole locations
• Type of joint (factory or field, tang or clevis)
• Tang index slots (at 0, 118, and 240 degrees)
• Leak check port location (at 0 degrees on tang)
• Insulation configuration
• Insulation thickness
• Inhibitor size and shape
• Propellant burnback pattern
• Part and serial number markings (where available)
• Exterior cork locations
• Exterior foam locations
• System tunnel remnants
• ET attach remnants
• Stub remnants for ET attach ring
• Stiffener ring remnants
• Case wall discoloration patterns
• Comparison of radar trajectory track to sonar location (latitude and longitude)
• Scaling known dimensions as a comparison base
• Paint pattern on forward skirt and frustum

[L91] D. Technical Description

Salvage Team sonar hardware contact numbers have been used herein, where available, to catalog each piece. The SRM Recovery Support Team located additional pieces from video tape reviews and used a lettering system for identification. A correlation between the two systems of artifact designation is provided in Table A-1.

A plot of the region where confirmed and suspected right booster fragments have been located is provided in Figure A-2. Debris Field 21 at the end of the right radar track contains numerous contacts identified as fragments of the right aft segment. Nine other confirmed or suspected right pieces are fragments of the booster forward of SRB Station 1577.48.

A pictorial drawing of the SRB configuration is provided in Figure A-3 for reference.

Using the previously mentioned identifying characteristics each major piece observed in one or more video tapes was characterized for size, shape and origin (right/left SRB and location). This process enabled a priority to be established for the KSC recovery activities with the pieces closest to the suspect joint given the highest priority. Schematics also helped to position other pieces with little or no identifying characteristics by the process of elimination.

Figures A-4 and A-5 illustrate the general area of the right and left SRB fragment orientations respectively. These figures also show the structural pieces of each booster which have been located and schematically oriented. Other booster fragments including the left SRB forward dome with ignitor, numerous nozzle pieces, TVC and other aft skirt parts have also been located. Examples of more detailed mapping of the various fragments are shown in Figures A-6 and A-7 for the right aft segment and aft center segment respectively.

Isometric sketches of several SRM fragments were made by the Salvage Support Team and provided to the SRM Recovery Support Team (Figures A-8 through A-21). The sketches were made primarily to support retrieval operations and depict the fragments as they appear on the ocean bottom. A schematic of the SRB has been added to each sketch to indicate the general area of the vehicle from which each fragment originated.

The identifications of a major portion of the right and left aft segments and aft skirt pieces were based on the theory that the aft segments of both boosters were, for the most part, intact at water impact. For the right booster, a major portion of the aft segment was located and mapped within an approximate 2.5 square mile (nautical) area at the end of the right radar track (Debris Field 21). From the structural pieces identified and schematically located in this debris field, no fragment has been found and schematically located forward of SRB Station 1577.48. This station is the first factory joint aft of the ET attach ring. It is therefore concluded that the right booster broke at this joint, most probably at command destruct. This conclusion is also supported by the fact that all other right booster pieces located, involving two pieces of the ET attach ring section Contacts 292 and 579), were found in a widely scattered area.

Debris Field 21 was confirmed to be that of right SRB fragments by the recovery of a hydraulic reservoir with an identifying serial number. SRB fragments found outside Debris Field 21 have been more widely scattered and have generally required identifying characteristics to establish whether they are right or left SRB fragments.

The following is a characterization for some of the fragments found, depicting the rationale used for identification and schematic orientation:

Contact 292, Designator "S" (Photograph A-1 and Figure A-14)

• - Section of Field joint Clevis
  • clevis legs remain
  • insulation design
• - Right Hand
  • sooted appearance
  • propellant quantity from burnback charts
  • ocean location south of right track
• - Aft Segment
  • ET attach stubs on piece
• - Located Schematically at 108 to 140 Degrees
  • hole pattern in attach stubs is 90 to 180 degrees pattern
  • no evidence of LSC cutting
  • no ablative compound over bolt holes
  • tape marks around one pin hole indicates assembly alignment for the 118-degree index

Contact 195, Designator "R" (Photograph A-2 and Figure A-15)

• - Section of Factory Joint Tang
  • joint section intact
  • insulation design
• - Section of Field Joint Clevis
  • clevis legs remain
  • insulation design
• - Right Hand
  • sooted appearance
  • propellant quantity from burnback charts
  • ocean location directly on right track
• - Forward Cylinder of Aft Center Segment
  • cylinder section piece
  • propellant location from burnback charts
• - Located Schematically at 90 to 250 Degrees
  • systems tunnel defines 90-degree edge
  • two index slots on tang (at 118 and 240 degrees)

Contact 301, Designator "Q" (Photograph A-3 and Figure A-16)

• - Section of Factory joint Clevis
  • clevis legs remain
  • insulation design
• - Section of Field joint Tang
  • joint intact
  • insulation design
• - Right Hand
  • sooted appearance
  • propellant quantity from burnback charts
  • ocean location close to right track
• - Aft Cylinder of Forward Segment
  • cylinder section piece
  • propellant location by joint from burnback charts
• - Located Schematically at 0 to 90 Degrees
  • leak check port defines 0 degrees
  • systems tunnel defines 90-degree edge
• - Confirmation
  • part and serial number steel stamped on part joint

E. Findings and Conclusions

STS 51-L visual flight data (film/video) showed a hot gas leak during ascent in the area of the Station 1491.48 field joint at approximately the 300-degree point. One significant fragment from the area of interest, Contact 131, Figures A-8, has been recovered and confirmed by part/serial number as a right aft cylinder of the aft center motor case segment. The fragment spans approximately 178 degrees with a section of the tang and adjacent case missing from 294 to 316 degrees. The edges of the "hole" which is approximately 28 by 15 inches show the effects of high heating and melting of the metal indicative of a burn through of the motor case at the suspect joint and location. This piece has been schematically located. The clevis portion of the joint has not been located. The second significant fragment from the area of interest, Contact 712, Figure A-22 (schematically located on Figure A-23) has been recovered and confirmed as a fragment of the right aft segment. The area between Contacts 131 and 712 has been estimated by dotted lines. A small hole is burned through the SRM case in the area of the lower ET strut. This small hole is 1.3 by 4 inches and is located near 315°.

Additionally, two other fragments, Contacts 292 (Figure A-14) and 579 (Figure A-9), from the joint of interest have also been recovered and located approximately 180 degrees from the suspect [L92] leak area. Both pieces, however, show no evidence of a leak (i.e., burning, melted metal, joint soot, etc.).

The primary failure mechanism of the motor case joints is tearing of the outside clevis leg. One exception is Contact 292 which had an area where the outer leg of the clevis was intact with the inner leg missing. As anticipated, the LSC cut the motor case clean and straight at the 90-degree point (systems tunnel area).

On the motor case segments forward of the ET attach ring, the fragments located between 0 and 90 degrees have predominantly fractured longitudinally through the leak check port at zero degrees.

No evidence of a severe heating environment, internal or external, has been detected on any of the fragments other than contact 131; i.e., no blistered paint or melted metal.

Sooting has been found in varying degrees on all right SRM external structural pieces identified. In general the left motor case pieces identified have a much cleaner appearance.

It appears that the right aft segment broke at the factory joint (Station 1577.48) prior to water impact. All aft segment pieces (identified) below Station 1577.48 fell in Debris Field 21. An estimated 85 percent of the aft segment has been schematically located. Contacts 292 and 579, which are above Station 1577.48, were located approximately 6.4 miles southwest of Debris Field 21 and 4 miles due east of Debris Field 21 respectively.

In general, right SRM pieces were found south of the right trajectory track and north of the left trajectory track. However, Contact 131, the most significant piece, was found south of the left trajectory track. Left SRM pieces were generally found south of the left trajectory track.

All forward and aft Booster Separation Motors (BSMs) from the right SRB have been located with no evidence any have been fired. The right nozzle LSC has also been viewed and apparently had not fired.

No portion of the ET attach struts or forward fitting has been located.

In conclusion, Contact 131 is the tang portion of the right motor case from the joint of interest. The location of the "hole" at the tang edge is consistent with the reported joint burn through and is significant evidence in the investigation of the STS 51-L incident. Contact 712 is the second major fragment of the motor case from the joint of interest. The location of the "hole" is consistent with the reported burn through and further enhances the evidence in the investigation of the STS 51-L incident.

Table A-1. Tape and Sketch Index

* "D" is designator.