http://smartech.gatech.edu/handle/1853/8331 Search the Channel search http://smartech.gatech.edu/simple-search http://smartech.gatech.edu/handle/1853/15067 Title: Survey of Global Optimization Methods for Low-Thrust, Multiple Asteroid Tour Missions <br/> <br/>Authors: Alemany, Kristina; Braun, Robert D. <br/> <br/>Abstract: Electric propulsion has recently become a viable option for robotic missions, enabling shorter flight times, fewer required planetary gravity assists, smaller launch vehicles, and/or larger payloads. Trajectory design of these missions often relies on local optimization of the low-thrust trajectories using starting points for departure and arrival dates and selection of gravitational swing-bys based on previous experience. Global optimization of a low-thrust trajectory with multiple targets and gravity assists, however, is a difficult problem, due to the multi-modality and large size of the design space. In choosing analysis techniques, there exists an important tradeoff between the accuracy of the results and computing time required. This paper presents the difficulty of solving this global optimization problem, using the design of a multiple asteroid tour mission as an example. Furthermore, this paper presents an overview of the methods available for both low-thrust trajectory optimization and global optimization, along with recent improvements made, and assesses their efficacy and applicability to solving a multiple target/multiple gravity assist problem. <br/> <br/>Description: 2007 AAS/AIAA Space Flight Mechanics Meeting January 2007, Sedona, Arizona. http://smartech.gatech.edu/handle/1853/14804 Title: Control Authority Network Analysis Applied to Lunar Outpost Deployment <br/> <br/>Authors: Alemany, Kristina; Morse, Elisabeth L.; Easter, Robert W. <br/> <br/>Abstract: In order to return humans to the Moon, the Constellation Program will be required to operate a complex network of humans and spacecraft in several locations. This requires an early look at how decision-making authority will be allocated and transferred between humans and computers, for each of the many decision steps required for the various mission phases. This paper presents an overview of such a control authority analysis, along with an example based upon a lunar outpost deployment scenario. The results illustrate how choosing an optimal control authority architecture can serve to significantly reduce overall mission risk, when applied early in the design process. <br/> <br/>Description: 2007 IEEE Aerospace Conference March 2007, Big Sky, MT. http://smartech.gatech.edu/handle/1853/14773 Title: An Approximate Ablative Thermal Protection System Sizing Tool for Entry System Design <br/> <br/>Authors: Dec, John A.; Braun, Robert D. <br/> <br/>Abstract: A computer tool to perform entry vehicle ablative thermal protection systems sizing has been developed. Two options for calculating the thermal response are incorporated into the tool. One, an industry-standard, high-fidelity ablation and thermal response program was integrated into the tool, making use of simulated trajectory data to calculate its boundary conditions at the ablating surface. Second, an approximate method that uses heat of ablation data to estimate heat shield recession during entry has been coupled to a one-dimensional finite-difference calculation that calculates the in-depth thermal response. The in-depth solution accounts for material decomposition, but does not account for pyrolysis gas energy absorption through the material. Engineering correlations are used to estimate stagnationpoint convective and radiative heating as a function of time. The sizing tool calculates recovery enthalpy, wall enthalpy, surface pressure, and heat transfer coefficient. Verification of this tool is performed by comparison to past thermal protection system sizings for the Mars Pathfinder and Stardust entry systems and calculations are performed for an Apollo capsule entering the atmosphere at lunar and Mars return speeds. <br/> <br/>Description: AIAA Aerospace Sciences Conference January 2006, Reno, NV. http://smartech.gatech.edu/handle/1853/14772 Title: Entry Descent and Landing Challenges of Human Mars Exploration <br/> <br/>Authors: Wells, Grant William; Lafleur, Jarret M.; Verges, Amanda; Manyapu, Kavya; Christian, John A., III; Lewis, Charity; Braun, Robert D. <br/> <br/>Abstract: Near-term capabilities for robotic spacecraft include a target of landing 1 - 2 metric ton payloads with a precision of about 10 kilometers, at moderate altitude landing sites (as high as +2 km MOLA). While challenging, these capabilities are modest in comparison to the requirements for landing human crews on Mars. Human Mars exploration studies imply the capability to safely land 40 - 80 metric ton payloads with a precision of tens of meters, possibly at even higher altitudes. New entry, descent and landing challenges imposed by the large mass requirements of human Mars exploration include: (1) the potential need for aerocapture prior to entry, descent and landing and associated thermal protection strategies, (2) large aeroshell diameter requirements, (3) severe mass fraction restrictions, (4) rapid transition from the hypersonic entry mode to a descent and landing configuration, (5) the need for supersonic propulsion initiation, and (6) increased system reliability. This investigation explores the potential of extending robotic entry, descent and landing architectures to human missions and highlights the challenges of landing large payloads on the surface of Mars. <br/> <br/>Description: 29th AAS Guidance and Control Conference February 2006, Breckenridge, CO.