# Browsing by Subject "Mission design"

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Item The application of systems engineering to a Space-based Solar Power Technology Demonstration Mission(2012-05) Chemouni Bach, Julien; Fowler, Wallace T.; Guerra, Lisa A.Show more This thesis presents an end-to-end example of systems engineering through the development of a Space-based Solar Power Satellite (SSPS) technology demonstration mission. As part of a higher education effort by NASA to promote systems engineering in the undergraduate classroom, the purpose of this thesis is to provide an educational resource for faculty and students. NASA systems engineering processes are tailored and applied to the development of a conceptual mission in order to demonstrate the role of systems engineering in the definition of an aerospace mission. The motivation for choosing the SSPS concept is two fold. First, as a renewable energy concept, space-based solar power is a relevant topic in today's world. Second, previous SSPS studies have been largely focused on developing full-scale concepts and lack a formalized systems engineering approach. The development of an SSPS technology demonstration mission allows for an emphasis on determining mission, and overall concept, feasibility in terms of technical needs and risks. These are assessed through a formalized systems engineering approach that is defined as an early concept or feasibility study, typical of Pre-Phase A activities. An architecture is developed from a mission scope, involving the following trade studies: power beam type, power beam frequency, transmitter type, solar array, and satellite orbit. Then, a system hierarchy, interfaces, and requirements are constructed, and cost and risk analysis are performed. The results indicate that the SSPS concept is still technologically immature and further concept studies and analyses are required before it can be implemented even at the technology demonstration level. This effort should be largely focused on raising the technological maturity of some key systems, including structure, deployment mechanisms, power management and distribution, and thermal systems. These results, and the process of reaching them, thus demonstrate the importance and value of systems engineering in determining mission feasibility early on in the project lifecycle.Show more Item Optimal lunar orbit insertion from a free return trajectory(2012-05) Jesick, Mark Christopher; Ocampo, Cesar; Fowler, Wallace; Hull, David; Marchand, Belinda; Russell, RyanShow more With the discovery of water ice at the moon's south pole, future human lunar exploration will likely occur at polar sites and, therefore, require high inclination orbits. Also of importance for human missions is the capability to abort if unfavorable circumstances arise. This dissertation addresses both of these concerns by creating an automated, systematic architecture for constructing minimum propellant lunar orbit insertion sequences while ensuring crew safety by maintaining a ballistic Earth return trajectory. To ensure a maneuver-free abort option, the spacecraft is required to depart Earth on a free return trajectory, which is a ballistic Earth-moon-Earth segment that requires no propulsive maneuvers after translunar injection. Because of the need for global lunar access, the required spacecraft plane change at the moon may be large enough that a multi-maneuver sequence offers cost savings. The combination of this orbit insertion sequence with the free return orbit increases the likelihood of a safe Earth return for crew while not compromising the ability to achieve any lunar orbit. A procedure for free return trajectory generation in a simplified Earth-moon system is presented first. With two-body and circular restricted three-body models, the algorithm constructs an initial guess of the translunar injection state and time of flight. Once the initial trajectory is found, a square system of nonlinear equations is solved numerically to target Earth entry interface conditions leading to feasible free return trajectories. No trial and error is required to generate the initial estimate. The automated algorithm is used to generate families of free return orbits for analysis. A targeting and optimization procedure is developed to transfer a spacecraft from a free return trajectory to a closed lunar orbit through a multi-maneuver sequence in the circular restricted three-body model. The initial estimate procedure is automated, and analytical gradients are implemented to facilitate optimization. Cases are examined with minimum time, variable symmetric, and general free returns. The algorithm is then upgraded to include a more realistic solar system model with ephemeris-level dynamics. An impulsive engine model is used before conversion to a finite thrust model. Optimal control theory is applied and the results are compared with the linearly steered thrust model. Trends in the flight time and propellant for various orbit insertion sequences are analyzed.Show more Item Preliminary interplanetary trajectory design tools using ballistic and powered gravity assists(2015-08) Brennan, Martin James; Fowler, Wallace T.; Russell, Ryan; Bettadpur, Srinivas; Lightsey, E G; Olsen, CarrieShow more Preliminary interplanetary trajectory designs frequently use simplified two-body orbital mechanics and linked conics methodology to model the complex trajectories in multi-body systems. Incorporating gravity assists provides highly efficient interplanetary trajectories, enabling otherwise infeasible spacecraft missions. Future missions may employ powered gravity assists, using a propulsive maneuver during the flyby, improving the overall trajectory performance. This dissertation provides a complete description and analysis of a new interplanetary trajectory design tool known as TRACT (TRAjectory Configuration Tool). TRACT is capable of modeling complex interplanetary trajectories, including multiple ballistic and/or powered gravity assists, deep space maneuvers, parking orbits, and other common maneuvers. TRACT utilizes an adaptable architecture of modular boundary value problem (BVP) algorithms for all trajectory segments. A bi-level optimization scheme is employed to reduce the number of optimization variables, simplifying the user provided trajectory information. The standardized optimization parameter set allows for easy use of TRACT with a variety of optimization algorithms and mission constraints. The dissertation also details new research in powered gravity assists. A review of literature on optimal powered gravity assists is presented, where many optimal solutions found are infeasible for realistic spacecraft missions. The need was identified for a mission feasible optimal powered gravity assist algorithm using only a single impulsive maneuver. The solution space was analyzed and a complete characterization was developed for solution types of the optimal single-impulse powered gravity assist. Using newfound solution space characteristics, an efficient and reliable optimal single-impulse powered gravity assist BVP algorithm was formulated. The mission constraints were strictly enforced, such as maintaining the closest approach above a minimum radius and below a maximum radius. An extension of the optimal powered gravity assist research is the development of a gravity assist BVP algorithm that utilizes an asymptote ΔV correction maneuver to produce ballistic gravity assist trajectory solutions. The efficient algorithm is tested with real interplanetary mission trajectory parameters and successfully converges upon ballistic gravity assists with improved performance compared to traditional methods. A hybrid approach is also presented, using the asymptote maneuver algorithm together with traditional gravity assist constraints to reach ballistic trajectory solutions more reliably, while improving computational performance.Show more