During development of a complex system, feasibility initially overshadows other concerns, in some cases leading to a design which may not be viable long-term. In particular for the case of Reusable Launch Vehicles, Operations&Maintenance comprises the majority of the vehicle's LCC, whose stochastic nature precludes direct analysis. Through the use of simulation, probabilistic methods can however provide estimates on the economic behavior of such a system as it evolves over time. Here the problem of operations optimization is examined through the use of discrete event simulation. The resulting tool built from the lessons learned in the literature review simulates a RLV or fleet of vehicles undergoing maintenance and the maintenance sites it/they visit as the campaign evolves over a period of time. The goal of this work is to develop a method for uncovering an optimal operations scheme by investigating the effect of maintenance technician skillset distributions on important metrics such as the achievable annual flight rate and maintenance man hours spent on each vehicle per flight. Using these metrics, the availability of technicians for each subsystem is optimized to levels which produce the greatest revenue from flights and minimum expenditure from maintenance.

This dissertation presents the development of a new concept and technology exploration methodology for aerospace architectures. The methodology is based on modeling the design space by a graph, and optimizing the graph using Ant Colony Optimization. The results show that the proposed design methodology can explore more efficiently the concept and technology space of a launch vehicle architecture than traditional optimization approaches such as Genetic Algorithm and Simulated Annealing. The purpose of the method is to introduce quantitative and simultaneous exploration of concept and technology alternatives during the early phases of conceptual design. To achieve this goal, technical challenges such as expanding the size of the design space, exploring more efficiently the design options, and simultaneously considering technologies and concepts are overcome. The total number of design alternatives grows factorially with the number of concepts in the design space. Under these circumstances, the design space is difficult to explore in its totality. Considering more alternatives has been the focus of several researchers, using Genetic Algorithms and Simulated Annealing. The large number of incompatibilities between alternatives, however, limits these optimization algorithms and reduces the number of concepts or technologies that can be considered. To address these problems, a concept and technology selection methodology is developed. The methodology proposes a way to automatically generate aerospace architectures, and to model concept and technology incompatibilities by means of a graph. In conjunction with this new modeling approach, a graph-based stochastic optimization algorithm is used to efficiently explore the design space. This design methodology is applied to the simultaneous concept and technology exploration of an expendable launch vehicle architecture. This study demonstrates that the consideration of more design alternatives can help design engineers to make more informed decisions during the concept and technology selection process. Moreover, the simultaneous exploration of concepts and technologies has the potential to identify a different set of solutions than the standard approach where the technologies are explored after the concepts have initially been selected.

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As advanced nozzles may offer alternative solutions to conventional nozzles for the future class of reusable launch vehicles, a critical aspect is to tailor these novel technologies to current recovery strategies, more specifically to vertical landing sustained by retro-propulsion. Researchers at Technische Universität Dresden have developed a dedicated test-bench for the vacuum wind tunnel facility, where Advanced Nozzle Concepts (ANCs), such as aerospike and dual-bell nozzles, are tested in cold-gas configuration while invested by subsonic counter-flows. The main objective of the test campaign is to evaluate the performance and altitude–compensation characteristics of such ANCs by simulating a vertical landing manoeuvre through the variation of ambient pressure experienced during the landing burn. A detailed description of design and development of the test-bench, together with preliminary results from the commissioning activities, are here offered to the reader. The force measurements, together with pressure and temperature data, contribute to evaluate thrust levels and coefficients, as well as the monitoring of the interaction between the nozzle cold-flow and the opposing free-stream. A background-oriented schlieren system allows to visualise the external flow-field. In conclusion, an outline of the upcoming test campaign and a description of the expected results is offered.

In a process monitoring/control applications tens to thousands of sensors are used for monitoring system parameters. To achieve overall system goals, their reliable performance is critical. Generally a sensor’s output signal is too small or too noisy and may not be compatible with the input requirements of a Data Acquisition System. The sensor is interfaced to Data Acquisition System, through cabling, junction boxes and Interface Electronics like excitation circuitry, multiplexers, signal-conditioning circuitry etc. An interface or signal conditioning circuit does impedance matching, filtering, multiplexing, pre-amplification, amplification and digitization to make the sensor’s output signal compatible with the Data Acquisition System. Conventional Signal Conditioning includes Multiplexers, Anti aliasing filters, Operational Amplifier, Instrumentation Amplifiers, Isolation Amplifiers and Charge Preamplifiers etc. Operational Amplifiers e.g. voltage followers with High input impedance and low output impedance are used for impedance matching between the sensor and processing electronics. Anti aliasing filters remove noise from the sensor’s output signal. Normally the sensor is located away from the processing electronics and data is transmitted through wires/cables. During transmission, interference from external fields’ especially strong Audio Frequency, Radio Frequency and 50Hz power line fields affects the sensor’s output signal. To minimize the effect of external field twisted pair shielded cables are used. Amplifiers with Differential input configuration are used to suppress the effect of interfering signals. Differential input Instrumentation Amplifiers with High input impedance, high CMRR; are most widely employed. Isolation Amplifiers isolate the input and output circuits by an extremely high impedance. Galvanic, optical isolations are most common. The conditioned data is transmitted to Data Acquisition System (DAS) and at the DAS the signal is multiplexed, filtered and digitized using Analog to Digital Converters (ADCs), followed by Digital Filtering and processing. For Control applications, the processed data is converted back to analog form using Digital to Analog Converters (DACs) for interfacing to external world. The transmission distance varies from tens of centimeters to few meters. Depending upon the distance twisted pair cables, IR transmission and Optical transmission is employed. During transmission, the data is prone to interferences from EMI, EMC, Noise and Signal to Noise ratio (SNR) degradation with distance. This affects the reliability of the system and increases the overall system cost. To eliminate the effects due to the environmental disturbances during transmission and to maintain signal integrity, it is preferred to have a unique and compact solution for each sensor where signal conditioning (excitation, filtering, amplification, compensation and digitization) is carried out and digital data can be transmitted to Data Acquisition System. Here each sensor has its own signal conditioning module. Directly interfacing sensors with micro controller yields simple and compact design solutions. Direct Sensor interface Technology (DSiT) is one of the state of the art technologies for sensor interfaces where an unconditioned, uncompensated, raw output signals from sensors are interfaced directly to a single-chip solution. The sensors’ output are multiplexed using Multiplexer; Amplified using Programmable Gain Amplifier (PGA), digitized using ADC, filtered using Digital Filters and transmitted using Digital Interfaces (SPI, I2C, UART) in a single chip. DSiT scheme incorporates all the elements necessary in an instrumentation system creating a balanced combination of features, to create truly intelligent sensor systems. The sensors are interfaced directly to a single DSiT chip, without any additional circuitry and the direct digital data transmission is achieved with the help of Digital Interfaces SPI, UART, SMBus/I2C. As this involves onchip signal conditioning and digital data transmission, expenditure on additional signal conditioning circuitry, analog interfaces for analog data transmission, separate Analog to Digital Converter for each sensor is reduced. This reduces the overall system cost and as the count of discrete components is reduced the system reliability is improved. In addition, as the data is transmitted digitally the effects of noise, S/N degradation and electromagnetic interferences are eliminated. The accuracy level achieved is sufficiently good for monitoring and control applications. In Launch Vehicles/Satellites number of sensors are used for performance evaluation, monitoring and control purposes. Harnessing, signal conditioning of the sensors’ output and onboard processing of the sensor data is carried out individually for each sensor. Implementation of the DSiT system will reduce the total weight of the launch vehicles and satellites, resulting in reduced overall system cost, increased reliability and reduced onboard processing overhead. In addition, the reduction in weight allows incorporation of larger payloads/ more propellant loading in payloads which increases the life of the Satellites. As it is compact, it can be readily used for facility parameter measurements during the ground testing of liquid engines and stages at LPSC/ISRO. Implementation of DSiT for facility parameter measurements will reduce the cabling cost and improve the reliability of the chain.

Master’s thesis deals with aerodynamic heating of launch vehicle during ascent phase by using CFD simulation. Ascent trajectory and payload fairing geometry is design using data of existing small launch vehicles. Critical flight regimes are identified using 2D calculations, and in these regimes analysis is performed by axially symmetric simulations. Simulation results are compared to values obtained from theoretical and semi-empirical calculations.

A satellite launch vehicle not subjected to any perturbations, external or internal, could be guided along a trajectory by following a stored, pre-computed steering program. In practice, perturbations do occur, and in order to take account of them and to achieve an accurate injection, a closed loop guidance system is required. Guidance algorithm is developed by solving the optimal control problem. Closed form solution is difficult because the necessary conditions are in the form of Two Point Boundary Value Problems (TBVP) or Multi Point Boundary Value Problems (MPBVP). Development of non-iterative guidance algorithm is taken as a prime objective of this thesis to ensure reliable on-board implementation. If non-iterative algorithms are required, the usual practice is to approximate the system equations to derive closed form solutions. In the present work, approximations cannot be used because the algorithm has to cater to a wide variety of vehicles and missions. Present development adopts an alternate approach by splitting the reconfigurable algorithm development in to smaller sub-problems such that each sub-problem has closed form solution. The splitting is done in such a way that the solution of the sub-problems can be used as building blocks to construct the final solution. By adding or removing the building blocks, the algorithm can be configured to suit specific requirements. Chapter 1 discusses the motivation and objectives of the thesis and gives a literature survey. In chapter 2, Classical Flat Earth (CFE) guidance algorithm is discussed. The assumptions and the nature of solution are closely analyzed because CFE guidance is used as the baseline for further developments. New contribution in chapter 2 is the extension of CFE guidance for a generalized propulsion system in which liquid and solid engines are present. In chapter 3, CFE guidance is applied for a mission with large pitch steering angles. The result shows loss of optimality and performance. An algorithm based on regular perturbation is developed to compensate for the small angle approximation. The new contribution in chapter 3 is the development of Regular Perturbation based FE (RPFE) guidance as an extension of CFE guidance. RPFE guidance can be configured as CFE guidance and FEGP. Algorithms presented up to chapter 3 are developed to inject a satellite in to orbits with unspecified inertial orientation. Communication satellite missions demand injection in to an orbit with a specific inertial orientation defined by argument of perigee. This problem is formulated using Calculus of Variations in chapter 4. A non-iterative closed form solution (Predicted target Flat Earth or PFE guidance) is derived for this problem. In chapter 5, PFE guidance is extended to a multi-stage vehicle with a constraint on the impact point of spent lower stage. Since the problem is not analytically solvable, the original problem is split in to three sub-problems and solved. Chapter 6 has two parts. First part gives theoretical analysis of the sub-optimal strategies with special emphasis to guidance. Behavior of predicted terminal error and control commands in presence of plant approximations are theoretically analyzed for a class of optimal control problems and the results are presented as six theorems. Chapter 7 presents the conclusions and future works.

A study was undertaken to determine if light-weighting orbital launch vehicles (rockets) improves lifetime environmental impacts of the vehicle. Light-weighting is performed by a material substitution where metal structures in the rocket are replaced with carbon fiber reinforced polymers (CFRP’s). It is uncertain whether light-weighting the rocket in the same way as traditional vehicles are light-weighted would provide similar environmental benefits. Furthermore, the rocket system is significantly different from traditional vehicles and undergoes an atypical lifecycle, making analysis non-trivial. Seventy rocket configurations were sized using a Parametric Rocket Sizing Model (PRSM) which was developed for this research. Four different propellant options, three staging options, and eighteen different lift capacities were considered. Each of these seventy rockets did not include CFRP’s, thus establishing a baseline. The seventy rockets were then light-weighted with CFRP’s, making a total of seventy pairs of rockets. An environmental Life Cycle Assessment (LCA) was performed on each of the rockets to determine lifetime environmental impacts. During the Life Cycle Inventory (LCI), a Carbon Fiber Production Model was developed to determine the environmental burdens of carbon fiber production and to address issues identified with carbon fiber’s embodied burdens. The results of the LCA were compared across all rockets to determine what effects light-weighting had on environmental impact. The final conclusion is that light-weighting reduces lifetime environmental impacts of Liquid Oxygen-Rocket Propellant 1 and Nitrogen Tetroxide-Unsymmetrical Dimethylhydrazine rockets, while it likely benefits Liquid Oxygen-Liquid Hydrogen rockets. Light-weighting increases lifetime environmental impacts of Solid Propellant rockets.