NASA Investigation Board Report On The INITIAL FLIGHT ANOMALIES OF SKYLAB 1

Significant Findings

1. The launch anomaly that occurred at approximately 63 seconds after lift-off was a failure of the meteoroid shield of the OWS.
2. The SAS-2 wing tie downs were broken by the action of the meteoroid shield at 63 seconds. Subsequent loss of the SAS-2 wing was caused by retro-rocket plume impingement on the partially deployed wing at 593 seconds.
3. The failure of the S-II interstage adapter to separate in flight was probably due to damage to the ordnance separation device by falling debris from the meteoroid shield.
4. The most probable cause of the failure of the meteoroid shield was internal pressurization of its auxiliary tunnel. This internal pressurization acted to force the forward end of the tunnel and meteoroid shield away from the OWS and into the supersonic air stream. The resulting forces tore the meteoroid shield from the OWS.
5. The pressurization of the auxiliary tunnel resulted from the admission of high pressure air into the tunnel through several openings in the aft end. These openings were: (1) an Imperfect fit of the tunnel with the aft fairing; (2) an open boot seal between the tunnel and the tank surface; and (3) open stringers on the aft skirt under the tunnel.
6. The venting analysis for the tunnel was predicated on a completely sealed aft end. The openings in the aft end of the tunnel thus resulted from a failure to communicate this critical design feature among aerodynamics, structural design, and manufacturing personnel.
7. Other marginal aspects of the design of the meteoroid shield which, when taken together, could also result in failure during launch are:

a. The proximity of the MS forward reinforcing angle to the air stream

b. The existence of gaps between the OWS and the forward ends of the MS

c. The light spring force of the auxiliary tunnel frames

d. The aerodynamic crushing loads on the auxiliary tunnel frames in flight

e. The action of the torsion-bar actuated swing links applying an outward radial force to the MS

f The inherent longitudinal flexibility of the shield assembly

g. The non-uniform expansion of the OWS tank when pressurized

h. The inherent difficulty in rigging for flight and associated uncertain tension loads in the shield.

8. The failure to recognize many of these marginal design features through six years of analysis, design and test was due, in part, to a presumption that the meteoroid shield would be "tight to the tank" and "structurally integral with the S-IVB tank" as set forth in the design criteria.
9. Organizationally, the meteoroid shield was treated as a structural subsystem. The absence of a designated "project engineer" for the shield contributed to the lack of effective integration of the various structural, aerodynamic, aeroelastic, test, fabrication, and assembly aspects of the MS system.
10. The overall management system used for Skylab was essentially the same as that developed in the Apollo program. This system was fully operational for Skylab; no conflicts or inconsistencies were found in the records of the management reviews. Nonetheless, the significance of the aerodynamic loads on the MS during launch was not revealed by the extensive review process.
11. No evidence was found to indicate that the design, development and testing of the meteoroid shield were compromised by limitations of funds or time. The quality of workmanship applied to the MS was adequate for its intended purpose.
12. Given the basic view. that the meteoroid shield was to be completely in contact with and perform as structurally integral with the S-IVB tank, the testing emphasis m ordnance performance and shield deployment was appropriate.
13. Engineering and management personnel on Skylab, on the part of both contractor and government, were available from the prior Saturn development and were highly experienced and adequate in number.
14. The failure to recognize these design deficiencies of the meteoroid shield, as well as to communicate within the project the critical nature of its proper venting, must therefore be attributed to an absence of sound engineering judgment and alert engineering leadership concerning this particular system over a considerable period of time.

Corrective Actions

1. If the back-up OWS or a similar spacecraft is to be flown in the future, a possible course of action is to omit the meteorold shield, suitably coat the OWS for thermal control, and accept the meteoroid protection afforded by the OWS tank walls. if, on the other hand, additional protection should be necessary, the Board is attracted to the concept of a, fixed, nondeployable shield.
2. To reduce the probability of separation failures such as occurred at the S-II interstage Second Separation Plane, both linear shaped charges should be detonated simultaneously from both ends. In addition, all other similar ordnance applications should be reviewed for a similar failure mode.
3. "Structural" systems that have to move or deploy, or that involve other mechanisms, equipment or components for their operation, should not be considered solely as a piece of structure nor be the exclusive responsibility of a structures organization.
4. Complex, multi-disciplinary systems such as the meteoroid shield should have a designated project engineer who is responsible for all aspects of analysis, design, fabrication, test and assembly.

Observations on the Management System

The Board found no evidence that the design deficiencies of the meteoroid shield were the result of, or were masked by, the content and processes of the management system that were used for Skylab. On the contrary, the rigor, detail, and thoroughness of the system are doubtless necessary for a program of this magnitude. At the same time. as a cautionary note for the future, it is emphasized that management must always be alert to the potential hazards of its systems and take care that an attention to rigor, detail and thoroughness does not inject an undue emphasis on formalism, documentation, and visibility in detail. Such an emphasis can submerge the concerned individual and depress the role of the intuitive engineer or analyst. It will always be of importance to achieve a cross-fertilization and broadened experience of engineers in analysis. design, test or operations. Positive steps must always be taken to assure that engineers become familiar with actual hardware, develop an intuitive understanding of computer-developed results, and make productive use of flight data in this learning process. The experienced "chief engineer," who can spend most of his time in the subtle integration of all elements of the system under his purview, free of administrative and managerial duties, can also be a major asset to an engineering organization.