Journal of Aerospace Engineering

Welding in space will be an important process for the permanent repair of both low- and high-pressure fluid line assemblies used on large spacecraft. Space station fluid systems are candidates for in-space repair. They provide a variety of tubing materials, sizes, pressures, and working fluids as well as including ancillary systems that demonstrate typical constraints to the repair process for a more realistic overall scenario. Damage to on-board fluid systems could occur as a product of faulty or fatigued joints, micrometeoroid impacts, collision with other objects, and over-pressure strain or burst. Incorporating terrestrial experience with automatic pipe-welding tools and that of both the U.S. and former Soviet space programs in space welding, hypothetical repair scenarios were analyzed using Space Station Freedom as a representative baseline. Weld joint design criteria are then derived. A new weld joint for in-space repair, which meets these system-derived criteria, is presented and a stress analysis is performed.

Automatic excavation has recently gained an increasing attention in industries such as construction, mining, and road works because of the need for cost-effectiveness as well as better safety for workers. Also, in remote work applications, like terrestrial sampling and cleaning of hazardous waste, there is a great need for automated excavation. In this paper, first a review and categorization of the previous work on the subject is carried out based on different aspects of the work associated with automating such a process. Then the nature of the excavation process is analyzed and the way it may be controlled is investigated.

A method for calculating compressible turbulent flows around an airfoil is presented. A modified low-Reynolds-number $k-\epsilon$ turbulence mode is used in the method to predict turbulent flows. The model is incorporated in a Navier-Stokes flow solver that is based on the cell-centered finite-volume method and Runge-Kutta multistage time-stepping scheme. Linear upwinding is used to specify the far-field boundary conditions for the turbulence transport equations. A limited amount of nonlinear numerical dissipation is introduced to ensure stable and converged results, but care is taken to ensure that the artificial viscosity is much smaller than the physical viscosity. Multigrid algorithm, implicit residual smoothing and local time stepping are used to achieve faster convergence of numerical solutions. Computational results for flows around a NACA 0012 airfoil are presented and discussed. Pressure distribution on the airfoil surface is compared with the corresponding measurement and good agreement is observed. Techniques that are used for solving the k and ε equations for stable and fast convergence are also presented and discussed.

A simplified design methodology is developed for the preliminary design of a proposed braced double-skinned roof structure for lunar applications, using Navier's and Levy's plate solutions. A finite-element analysis of the structure is performed to evaluate the accuracy of the design methodology. Results from extensive parametric studies are used to select the final dimensions of the braced double-skinned roof assembly for realistic static loading. The natural frequencies of the proposed roof structure are evaluated by a simplified relation and are compared with those obtained by the finite-element method.