Development of Predictive Ballistic Models for Hypervelocity Impact on Sandwich Panel Satellite Structures

Sandwich panels are widely used in the design of uninhabited satellites and, in addition to having a structural function can often serve as shielding, protecting the satellites’ equipment from hypervelocity impacts (HVI) of orbital debris, and micrometeoroids. This thesis aims to provide: a comprehensive review of HVI experimental studies for honeycomb- and open-cell foam-cores; an examination of available predictive models used to assess the panels’ ballistic limits; as well as signify the influence of honeycomb-core parameters, such as cell size and foil thickness, as well as core material, on the ballistic performance of honeycomb-core sandwich panels (HCSP) when subject to HVI scenarios. To study the influence of HCSP parameters, two predictive models: a dedicated ballistic limit equation (BLE)—based on the Whipple shield BLE—and an artificial neural network (ANN) trained to predict the outcomes of HVI on HCSP were developed. A database composed of physical and numerical simulations allowed for BLE fitting and ANN training. The ANN was developed using MATLAB’s Deep Learning Toolbox framework and was tuned using a comprehensive parametric study to optimize the ANN architecture, including such parameters as the activation function, the number of hidden layers and the number of nodes per layer. The predictive models were verified using a new set of simulation data and achieved low error percentage in comparison when predicting the ballistic limits of HCSP, ranging from 1.13% to 5.58% (BLE) and 0.67% and 7.27% (ANN), respectfully

Feasibility of the motorized momentum exchange tether system: an investigation of system risk

This thesis examines the feasibility of a motorized momentum exchange tether (MMET) system being used to perform commercial space launches. The MMET system is an on-orbit launch concept that could be used to reduce the cost of access to space, thereby catalysing a broader range of space-enabled business concepts. The research presented in this thesis assumes this cost of access to space for a reasonable launch system can be presented as the adverse financial risk of its operation. Under this assumption, the research concludes that an MMET-based system would be a feasible alternative to an equivalently capable conventional system if the risk associated with the system is less than that associated with the alternative. To illustrate the concepts and approaches presented within, this thesis presents an assessment of the proposed Lunar Staged MMET (LSM) mission, an assessment that indicates the MMET is a feasible alternative for completing such a mission under specific analytical and market conditions. The expected financial risk is presented in this thesis as the product of the mission cost and the probability of mission failure. The cost of each mission is calculated from the perspective of the end customer, and the long-term price of such services is computed using publicly available data and the assumption that the commercial space industry can be modelled as an oligopoly. Support for such a model is contained in the literature and through this research, which compares the quarterly financial data published by the Boeing Company against the international commercial launch rate. The probability of system failure associated with an MMET-based unconventional launch system must account for a number of factors. For the first, conventional stage of the system, assessing the probability of stage failure is found through an examination of observed failure rates relative to conventional engineering reliability estimates for conventional launch vehicles. Through this examination, a novel approach to calculating the rate at which the probability of failure for vehicles produced within a variant class changes as a function of time is presented, an approach that offers a valid technique for applying reliability growth across a series of vehicles that are best considered to be independent vehicles. The thesis goes on to present the results of research into various component aspects that are vital to the design and analysis of a tether-based system. First, the research explores the strength of tethers modelled as braided aramid ropes, which supports claims of strain dependence regarding aramid fibre strength that can have significant strength benefits and indicates that this phenomenon should be accounted for in any operational architecture. Second, the thesis presents an empirical hypervelocity impact effects equation calibrated for use with tethers, which indicates that the currently accepted approach to oblique hypervelocity impacts may not be appropriate for tether analyses. Thirdly, research into fractured impactor dispersion after a hypervelocity impact on tether targets is presented, which indicates that the commonly accepted one-impact- one-failure assumption employed for multi-line tether analyses may not be sufficient. TetherLife, an analytical program developed to calculate the expected lifetime of an MMET system given various sub-span parameters, employs the products of these research areas to calculate the mean time to failure for a range of tether sizes and orientations. After combining the probability of failure associated with the conventional launch vehicle component of the MMET-based unconventional launch system, the probability of failure associated with the MMET system, the probability or failure associated with handing a payload between systems, and the likely cost of deploying a suitable set of MMET systems, a comparison can be made between the financial risk associated with completing a specific mission using an MMET based unconventional launch system verses completion of the same mission using conventional means. For the LSM mission examined within the research, an MMET-based system would be a reasonable option if an average of 85 missions per year are required, contingent on specific analytical assumptions. While such a number of lunar supply missions are not currently required, the conclusion that the MMET system can be an alternative to a conventional system under various circumstances offers support for continuing current research on system design and analysis

After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission

NASA’s Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ∼10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos’s response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor β, showing that a particular direction-specific β will be directly determined by the DART results, and that a related direction-specific β is a figure of merit for a kinetic impact mission. The DART β determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos’s near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction

After DART: Using the first full-scale test of a kinetic impactor to inform a future planetary defense mission

NASA's Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ~10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos's response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor $\beta$, showing that a particular direction-specific $\beta$ will be directly determined by the DART results, and that a related direction-specific $\beta$ is a figure of merit for a kinetic impact mission. The DART $\beta$ determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos's near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in-situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction