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NASA's development of new concepts for the Crew Exploration Vehicle Orion presents many similar challenges to those worked in the 1960s during the Apollo programme. However, with improved modelling capabilities, new challenges arise. For example, the use of the commercial code LS-DYNA, although widely used and accepted in the technical community, often involves high-dimensional, time-consuming and computationally intensive simulations. Because of the computational cost, these tools are often used to evaluate specific conditions and are rarely used for statistical analysis. This paper discusses an approach to capture what is learned from a limited number of LS-DYNA simulations to develop models that allow users to conduct interpolation of solutions at a fraction of the computational time. In this approach, response surface models are used to predict the system time responses to a water landing as a function of capsule speed, direction, attitude, water speed and water direction. Furthermore, these models can also be used to ascertain the adequacy of the design in terms of probability measures. This paper presents a description of the LS-DYNA model, a brief summary of the response surface techniques, the analysis of variance approach used in the sensitivity studies, equations used to estimate impact parameters, results showing conditions that might cause injuries and concluding remarks. [ABSTRACT FROM AUTHOR]

Abstract: High strength woven fabrics are ideal candidate materials for use in structural systems where high energy absorption is required. One of the more widely used applications for woven fabrics is in propulsion engine containment systems. In this first part of a two-part paper, details of the experiments to characterize the behavior of dry fabrics including Kevlar® and Zylon® are presented. The experimental program to characterize the behavior of 1420 Denier Kevlar® 49 17×17, 500 Denier Zylon® AS 35×35, and 1500 Denier Zylon® 17×17 are discussed. The primary objective is to use the experimental results in the development of a constitutive model that can be used in an explicit finite element analysis program. These include Tension Tests in both the warp and fill directions of the fabric, Trellising Shear Tests and Friction Tests between fabric layers. The results from these tests provide the basis for development of the constitutive model – relating stresses to strains, characterizing failure and interaction between fabric layers. In addition to these basic material tests, tests on systems built with fabric wraps were also conducted. Ballistic tests of containment wraps subjected to a high velocity projectile were carried out at NASA-Glenn Research Center. While these tests provide a comparison between the energy absorbing characteristics of the three fabrics, they also provide benchmark results to validate the developed finite element methodology discussed in the second part of this paper. [Copyright &y& Elsevier]

Abstract: Breakup model is the key area of space debris environment modeling. NASA standard breakup model is currently the most widely used for general-purpose. It is a statistical model found based on space surveillance data and a few ground-based test data. NASA model takes the mass, impact velocity magnitude for input and provides the fragment size, area-to-mass ratio, velocity magnitude distributions for output. A more precise approach for spacecraft disintegration fragment analysis is presented in this paper. This approach is based on hypervelocity impact dynamics and takes the shape, material, internal structure and impact location etc. of spacecraft and impactor, which might greatly affect the fragment distribution, into consideration. The approach is a combination of finite element and particle methods, entitled finite element reconstruction (FER). By reconstructing elements from the particle debris cloud, reliable individual fragments are identified. Fragment distribution is generated with undirected graph conversion and connected component analysis. Ground-based test from literature is introduced for verification. In the simulation satellite targets and impactors are modeled in detail including the shape, material, internal structure and so on. FER output includes the total number of fragments and the mass, size and velocity vector of each fragment. The reported fragment distribution of FER shows good agreement with the test, and has good accuracy for small fragments. [Copyright &y& Elsevier]

NASA's effort to develop a large payload, high altitude, long-duration balloon, the ultralong duration balloon, focuses on a pumpkin shape superpressure design. It has been observed that a pumpkin balloon may be unable to pressurize into the desired cyclically symmetric equilibrium configuration, settling into a distorted, undesired state instead. Hoop stress considerations in the pumpkin design lead to choosing the lowest possible bulge radius, whereas robust deployment is favored by a large bulge radius. Mechanical locking may be a contributing factor in the formation of undesired equilibria. Long term success of the pumpkin balloon for NASA requires a thorough understanding of the phenomenon of multiple stable equilibria. This paper uses the notion of stability to classify balloon designs. When we applied our finite element model to a balloon based on the NASA Phase IV-A pumpkin design, we found the fully inflated/fully deployed strained equilibrium float configuration was unstable. To demonstrate our approach for exploring the stability of constant bulge radius designs and their sensitivity to parameter changes we carry out a number of parametric studies. We focus on analytical studies, but we also compare our results with flight data whenever possible. [ABSTRACT FROM AUTHOR]