Engineering topics
Publications and source records attributed to Vaughn, Timothy P..
The primary objective of full scale development is to mitigate scale-up issues before the vehicle ever reaches production and verify assembly design models. Only at full scale can the true challenges associated with production be identified and dealt with. Also, only at full scale can the delta shift between lab and subscale hardware manufacture and assembly be assessed.
A major cause of project failure can be attributed to an emphasized focus on end products and inadequate attention to resolving development risks during the initial phases of a project. The initial phases of a project, which we will call the "study period", are critical to determining project scope and costs, and can make or break most projects. If the requirements are not defined adequately, how can the scope be adequately determined, also how can the costs of the entire project be effectively estimated, and how can the risk of project success be accurately assessed? Using the proper material specifications and standards and incorporating these specifications and standards in the design process should be considered inherently crucial to the technical success of a project as just as importantly, crucial to the cost and schedule success. This paper will intertwine several important aspects or considerations for project success: 1) Characteristics of a "Good Material Requirement"; 2) Linking material requirements to the implementation of "Design for Manufacturing"; techniques and 3) The importance of decomposing materials requirements during the study phase/development phase to mitigate project risk for the maturation of technologies before the building of hardware.
The Cryogenic Tank Technology Program (CTTP) program has been a cooperative effort between NASA LARC, NASA MSFC, NASA Headquarters, and industry (Lockheed Martin Aeronautics, Lockheed Martin Manned Space Systems, Wyman Gordon, and Ladish). The scope of the CTTP is to develop state-of-the-art, flight-size, flight-quality, low cost hardware, and use this hardware to design, fabricate and test an all aluminum-lithium, all near net shape-component 14' diameter cryogenic tank with a unique low profile bulkhead design. The logical conclusion to the CTTP is to validate these various technologies to a Technology Readiness Level (TRL) of 6 through the proposed structural test program. The CTTP supports the advancement of key enabling technologies required for aluminum lithium cryogenic tanks. The technologies are focused towards innovative and low cost manufacturing processes such as near net shape technologies: one piece spun formed domes, extruded barrel panels, and one piece roll forged ring frames. Other innovative technologies include the friction stir weld process and weight-efficient low profile bulkhead designs. All of these technologies are of primary importance for NASA's mission plan for reusable and expendable launch vehicles. This program fills the niche for an all 2195 aluminum lithium alloy cryogenic tank which is not being covered by existing NASA technology work.
The development of reusable launch vehicle systems for a single stage to orbit vehicle requires vehicles at liftoff with 85% to 94% of its mass consisting exclusively of propellants. These dry mass requirements drive designs to utilize stronger, lighter weight materials for structures. This technology development focus has allowed the introduction of composite materials in lieu of conventional metallic materials due to their higher specific strengths. Composite materials were successfully used for the liquid hydrogen tanks for the DC-XA, and a multi-lobed liquid hydrogen tank will be employed for the X-33. Another potential non-traditional application for composite materials is for liquid oxygen tanks, which is still being investigated. Traditionally, organic materials have been avoided wherever possible, due the potential fire hazard and the fact that composites fail conventional oxygen compatibility requirements. However, the potential weight savings warrant the investigation of the use of polymeric composite materials in oxygen environments. Since composites fail the conventional, time-proven test methods because they are considered flammable by test, we have embarked on an innovative approach to oxygen compatibility testing and evaluation focused on the use environments and attempts to eliminate or "design away" all potential ignition sources. Oxygen compatibility is defined as the ability of a material to coexist with oxygen and potential ignition sources with an acceptable, manageable degree of risk.