Design and Evaluation of a Reinforced Advanced-Grid Stiffened Composite Structure
Abstract : A composite grid-stiffened structure concept was selected for the payload fairing of the Minotaur launch vehicle. Compared to previous designs, this concept is lighter weight and requires reduced manufacturing costs. Various failure mechanisms were examined for the composite grid-stiffened structure. The controlling criterion for this design was determined to be joint peel-off failure. The identification of this failure mechanism and the assessment of bounding strains to control it, required extensive test and analysis effort. The final fairing design incorporated an undesirably thick skin to reduce the strain between the skin and ribs. This project investigated a means of controlling joint failure of the un-reinforced grid-stiffened structure in an effort to reduce the skin thickness. Implementing lightweight foam inserts between the stiffeners on the interior of the fairing delayed failure to higher loads. A foam reinforced test panel, designed with equal mass to the current structure, withstood a substantially greater compressive force. The alternative concept also demonstrated an improved response, failing in global buckling instead of experiencing early failure due to joint strain.
Advanced Iso-Grid Fairing Qualification Test for Minotaur Launch Vehicle
Abstract : The development of the grid-stiffened fairing to be flown on the Minotaur launch vehicle has made significant progress over the past five years. This qualification structure was subjected to static qualification testing. The 6 m (20 ft) tall fairing was constrticted of a carbon fiber composite grid structure that was over-wrapped to create a laminated skin. Upon completion of curing and machining, the fairing was cut in half to create the classic clam shell fairing. Metallic joints were bonded and fastened to the fairing at all interfaces to complete the assembly process and simulate attachment of the base to a launch vehicle. Static qualification of the fairing tested the integrity of the fairing, thereby proving the design and manufacturing process. Loads were applied incrementally in a static loading scenario. The applied load envelope exceeded worst case dynamic flight conditions with an added safety factor of 25%. At peak load the fairing must maintain stiiictural integrity remaining within the defined dynamic displacement envelope.
Application of Advanced Grid-Stiffened Structures Technology to the Minotaur Payload Fairing
Abstract : The Air Force Research Laboratory Space Vehicles Directorate (AFRL/VS) is exploring new structural configurations and corresponding methods for fabricating launch vehicle fairings. The goal of this research is to reduce the cost of these components while also enabling large structures to be fabricated. Processes for fabricating Advanced Grid Stiffened (AGS) composite structures have been developed that show promise to help achieve these goals. These procedures were successfully demonstrated in an AGS fairing for the Ballistic Missile Defense Organization's (BMDO) Combined Experiments Program. Currently, AFRL/VS has joined with Boeing's Phantom Works and Orbital Sciences Corp (OSC) to develop an extended fairing for the Orbital Suborbital Program's Minotaur launch vehicle. The design methods, fabrication procedures, and testing plans used to develop this fairing will be discussed.