Design and Testing of All-Composite Connections for Launch Vehicle Payload Adapters

The Air Force Research Laboratory, Space Vehicles Directorate, is currently investigating several composite design configurations for all composite bolted connection flanges. These efforts have been directed toward adapter connections for the Evolved Expendable Launch Vehicle (EELV). Designs were investigated and tested for the EELV Secondary Payload Adapter (ESPA) and for EELV 4 and 5-meter conic payload adapter variations with a 1780 mm forward connection diameter. These adapters support the payload(s) on the launch vehicle and must be carried to orbit with the payload. The original ESPA adapter design was conceived and developed as an aluminum ring structure to support a main payload and a cluster of six smaller payloads (each weighing a few hundred kilograms). Specimens with composite connections were designed fabricated by ATK and tested by AFRL. These were compared to the response of an ESPA equivalent aluminum substructure. Acceptable structure response was identified for several or these composite design alternatives. The 1780 mm payload adapter is being designed by Boeing (Huntington Beach) and built by ATK (Salt Lake City, UT and Iuka, MS) to provide improved adaptability to a variety of future commercial Delta IV and EELV missions. The design forces introduce high interlaminar tension stress at the bend of the flange. The resulting design makes limited use of composite Z-pinning to reinforce critical sections. Substructures were fabricated by ATK and designed and tested by Boeing. Additionally a complete conic substructure of the forward 50 cm of the adapter containing the composite forward flange has been built by ATK in Iuka, MS. AFRL tested this structure and the test results confirm that this composite flange can be used for a final design of the adapter shell.