Projectile Shape and Material Effects in Hypervelocity Impact Response of Dual‐Wall Structures

All large spacecraft are susceptible to impacts by meteoroids and pieces of orbiting space debris. These impacts occur at extremely high speeds and can damage flight‐critical systems, which can in turn lead to catastrophic failure of the spacecraft. A long‐duration spacecraft developed for a mission into this environment must include adequate protection against perforation of pressurized components by such impacts. This paper presents the results of an investigation into the effects of projectile shape and material on the perforation of aluminum dual‐wall structural systems. Impact damage is characterized according to the extent of perforation, crater, and spall damage in the structural systems as a result of hypervelocity projectile impact loadings. Analysis of the damage data shows that there are distinct differences in impact damage from cylindrical and sherical projectiles. Projectile density is also found to affect the type and extent of damage sustained by dual‐wall structural systems.     

Characterizing Debris Clouds Created in Oblique Orbital Debris Particle Impact

The problem of pollution within Earth’s orbital environment has gained considerable recognition over the past decades. Determining adequate passive protection schemes is an unending process that attempts to meet different objectives for widely varying types of missions. Significant amounts of resources have been expended toward development of numerical and analytical models that model the response of a variety of target systems under high-speed orbital debris impacts. The objective of the study whose results are presented herein was to improve upon an existing oblique hypervelocity impact model that characterizes the various secondary debris clouds created in such an impact. This was accomplished by reducing the model’s dependence on empirical user-defined parameters and by correcting an error in one of its equations. Predictions of the improved model are compared with numerical simulations generated during previous impact studies under comparable conditions. It is found that the improved model does a reasonable job of predicting the characteristics of the secondary debris clouds created in an oblique hypervelocity impact.     

Shuttle Debris Impact Analysis: Postreturn to Flight Real-Time Mission Support

Prior to the Columbia accident, quantitative impact assessment tools were not available to analyze debris impacts onto the Shuttle’s thermal protection system. Following the accident, the Columbia Accident Investigation Board recommended changes to increase the safety of future shuttle flights; one component was the development of physics-based analytical capabilities to evaluate damage due to debris impacts. This paper will present an overview of real time debris assessment impact analysis conducted by the Boeing Philadelphia Advanced Structural Analysis Impact Analysis Team in support of Space Shuttle missions since Return to Flight, the first mission after the Columbia accident. Specifically, analyses performed in support of missions STS-114, 121 and 117 will be presented. For each of these cases, an overview of the structural and material model development will be provided, and results of each analysis will be presented followed by a discussion of how the results lead into real time mission decisions. This work illustrates the importance of maintaining a physics-based real-time analysis capability as a vital instrument in supporting the safety of future spaceflight missions.     

Some Comments on the Protection of Lunar Habitats against Damage from Meteoroid Impacts

The establishment of human habitats on the Moon and on Mars will require protecting them from the hazards of near-Earth and interplanetary space. In addition to solar radiation, another hazard to be faced by these habitats is the damage that can result from the high speed impact of a meteoroid on a critical structural component. Therefore, lunar habitats and their accompanying support facilities need to be designed with adequate levels of protection that will allow them to also withstand the damage that can result from a meteoroid impact. In this paper we discuss some approaches to shielding for lunar habitats, focusing on shielding that is intended primarily to provide protection against meteoroid impacts and on shielding approaches that use resources mined or extracted from the Moon. The Moon’s mineralogy is discussed and suggestions are presented for materials and material combinations that can be used to develop shielding for lunar habitats and which are comprised primarily or entirely of lunar materials. Several shielding mechanisms are also presented that could be effective against impacts by meteoroid particles having diameters on the order of that which are likely to strike a fairly large lunar habitat at least one or two times per year. The paper concludes with recommendations for continuing work in optimizing the design of meteoroid shielding for lunar habitats.     

Breakage Prediction of Laminated Glass Using the “Sacrificial Ply” Design Concept

Laminated architectural glass has proven to be well suited for use in glazing systems that must resist wind-borne debris impacts. When the inner glass ply in a laminated window unit remains unbroken after wind-borne debris impacts on the outer glass ply, the integrity of the building envelope is preserved. A mechanics-based analytical model is developed to predict the cumulative probability of inner glass ply breakage in laminated architectural glass subjected to simulated wind-borne debris impacts on the outer glass ply. A nonlinear dynamic finite-element analysis is employed to compute stresses in each layer of the laminate due to impact. Based on the cumulative damage theory, the two-parameter Weibull distribution is used to characterize the cumulative probability of inner glass ply breakage. The analytical predictive model is calibrated using available experimental data on material parameters. Cumulative probabilities of inner glass ply breakage predicted by the analytical model are in agreement with the corresponding experimental data.     

Isssues in Developing Control Zones for International Space Operations

As the number of space‐faring nations and orbiting spacecraft increases, it is desirable to develop an international traffic‐management strategy to coordinate, monitor, and control the interactions of spacecraft in orbit. Successful strategies will facilitate cooperative missions while still supporting each nation's unique goals and objectives in space. The potential benefits of such a strategy include: reductions in future program costs and increases in mission success through the standardization of space operations and equipment; increased safety through development of a coordinated collision avoidance strategy for active spacecraft and debris; and establishing a basis for legal and economic compensation agreements. One means of implementing such a strategy is to utilize a control zones technique that assigns different types of orbital operations to specific regions of space surrounding a vehicle. This paper considers the issues associated with developing a control‐zones technique to regulate the interactions of spacecraft in proximity to a manned vehicle. It includes discussion of technical and planning issues, flight hardware and software issues, mission‐management parameters, and other constraints. It addresses manned and unmanned vehicle operations, and manual versus automated flight control. A review of the strategies utilized by the Apollo‐Soyuz Test Project and the Space Station Freedom Program is also presented.     

Multiterrain Earth Landing Systems Applicable for Manned Space Capsules

A key element of the President’s Vision for Space Exploration is the development of a new space transportation system to replace Shuttle that will enable manned exploration of the moon, Mars, and beyond. The National Aeronautics and Space Administration has created the Constellation Program to develop this architecture, which includes the Ares launch vehicle and Orion manned spacecraft. The Orion spacecraft must carry six astronauts and its primary structure should be reusable, if practical. These requirements led the Constellation Program to consider a baseline land landing on return to earth. To assess the landing system options for Orion, a review of current operational parachute landing systems such as those used for the F-111 escape module and the Soyuz is performed. In particular, landing systems with airbags and retrorockets that would enable reusability of the Orion capsule are investigated. In addition, Apollo tests and analyses conducted in the 1960s for both water and land landings are reviewed. Finally, test data and dynamic finite-element simulations are presented to understand land landings for the Orion spacecraft.     

Computational Technique to Assess Warhead Lethality against Ballistic Missile

This paper addresses a computational procedure to assess the lethality of kinetic energy projectile warheads against tactical ballistic missile payloads with an innovative and rational damage metric. The individual lethality of different projectile geometries impacting at hypervelocity at different configurations is estimated via a numerical damage index computed from hydrocode simulations. The highest count of possible impacts to the payload is achieved by optimizing the warhead’s configuration and time of detonation, a priori knowledge of the target’s location and speed. The total damage to the payload characterizes the warhead’s lethality for the particular engagement conditions. An example shows the application of the process and potential advantages.     

Transition from Nondeformable Projectile Penetration to Semihydrodynamic Penetration

With the increase of impact velocity, penetration mechanism may change at a transition point from nondeformable projectile penetration regime to semihydrodynamic penetration regime. Analysis is presented to predict this transition point. Good agreements between analytical predictions and experimental results are obtained.     

Space Structures: Issues in Dynamics and Control

A selective technical overview is presented on the vibration and control of large space structures, the analysis, design, and construction of which will require major technical contributions from the civil∕structural, mechanical, and extended engineering communities. The immediacy of the U.S. space station makes the particular emphasis placed on large space structures and their control appropriate. The space station is but one part of the space program, and includes the lunar base, which the space station is to service. This paper attempts to summarize some of the key technical issues and hence provide a starting point for further involvement. The first half of this paper provides an introduction and overview of large space structures and their dynamics; the latter half discusses structural control, including control‐system design and nonlinearities. A crucial aspect of the large space structures problem is that dynamics and control must be considered simultaneously; the problems cannot be addressed individually and coupled as an afterthought.