Organizational Unit:

Aerospace Systems Design Laboratory (ASDL)

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https://hdl.handle.net/1853/70744

Parent Organization

Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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https://finding-aids.library.gatech.edu/agents/corporate_entities/1135

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Publication Search Results

Now showing 1 - 10 of 25

Technology Readiness Level, Schedule Risk and Slippage in Spacecraft Design: Data Analysis and Modeling

(Georgia Institute of Technology, 2007-09) Dubos, Gregory F. ; Saleh, Joseph H. ; Braun, Robert D.

Schedule slippage plagues the space industry, and is antinomic with the recent emphasis on space responsiveness. The Government Accountability Office has repeatedly noted the difficulties encountered by the Department of Defense in keeping its acquisition of space systems on schedule, and identified the low Technology Readiness Level (TRL) of the system/payload under development as a principal culprit driving schedule risk and slippage. In this paper, we analyze based on data from past space programs the relationship between technology uncertainty and schedule risk in the acquisition of space systems, and propose an analytical framework to identify appropriate schedule margins for mitigating the risk of schedule slippage. We also introduce the TRL-schedule-risk curves to help program managers make riskinformed decisions regarding the appropriate schedule margins for a given program, or the appropriate TRL to consider should the program’s schedule be exogenously and rigidly constrained. We recommend based on our findings, that the industry adopts and develops schedule risk curves (instead of single schedule point estimates), 2) that these schedule risk curves be made available to policy- and decision-makers in acquisition programs; and 3) that adequate schedule margins be defined according to an agreed upon and acceptable schedule risk level.
Design Space Pruning Techniques for Low-Thrust, Multiple Asteroid Rendezvous Trajectory Design

(Georgia Institute of Technology, 2007-09) Alemany, Kristina ; Braun, Robert D.

In 2006, the 2nd Global Trajectory Optimization Competition (GTOC2) posed a “Grand Asteroid Tour” trajectory optimization problem, where participants were required to find the best possible low-thrust trajectory that would rendezvous with one asteroid from each of four defined groups. As a first step, most teams employed some form of design space pruning, in order to reduce the overall number of possible asteroid combinations. Because of the large size of the problem, teams were not able to determine if their pruning technique had successfully eliminated only bad solutions from the design space. Therefore, a small subset of the GTOC2 problem was analyzed, and several design space pruning techniques were applied to determine their effectiveness. The results indicate that the pruning techniques chosen by the participants likely eliminated good solutions from the design space, because they either did not accurately represent the low-thrust problem or could not be considered independently without the effect of other factors.
Mars Gravity Biosatellite: Engineering, Science, and Education

(Georgia Institute of Technology, 2007-09) Korzun, Ashley M. ; Braun, Robert D. ; Wagner, Erika B. ; Fulford-Jones, Thaddeus R.F. ; Deems, Elizabeth C. ; Judnick, Daniel C. ; Keesee, John E.

The Mars Gravity Biosatellite is a novel program aimed at providing data on the effects of partial gravity on mammalian physiology. Physiological problems intrinsic to prolonged stays in microgravity have long been concerns of manned spaceflight and will continue to be a significant obstacle in achieving the goals outlined in NASA’s Vision for Space Exploration. This student-developed, free-flyer spacecraft is designed to carry a payload of 15 mice into low Earth orbit, rotating to generate an acceleration environment equivalent to Martian gravity. After 35 days, the payload will be de-orbited and recovered for study. Data collected during the mission and post-recovery will be used to characterize the physiological changes incurred under partial gravity conditions and validate the models used in designing the spacecraft. This paper presents the preliminary design of the spacecraft. By providing groundbreaking flight data on the effects of partial gravity on mammalian physiology and engaging over 500 students to date, the Mars Gravity Biosatellite program is working to enable successful human exploration of the Moon and Mars while training and inspiring a new generation of scientists and engineers.
Survey of Global Optimization Methods for Low-Thrust, Multiple Asteroid Tour Missions

(Georgia Institute of Technology, 2007-01) Alemany, Kristina ; Braun, Robert D.

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.
Improving Lunar Return Entry Footprints Using Enhanced Skip Trajectory Guidance

(Georgia Institute of Technology, 2006-09) Putnam, Zachary R. ; Braun, Robert D. ; Bairstow, S. H. ; Barton, G. H.

The impending development of NASA's Crew Exploration Vehicle (CEV) will require a new entry guidance algorithm that provides sufficient performance to meet all requirements. This study examined the effects on entry footprints of enhancing the skip trajectory entry guidance used in the Apollo program. The skip trajectory entry guidance was modified to include a numerical predictor-corrector phase during atmospheric skip portion of the entry trajectory. Four degree-of-freedom simulation was used to determine the footprint of the entry vehicle for the baseline Apollo entry guidance and predictor-corrector enhanced guidance with both high and low lofting at several lunar return entry conditions. The results show that the predictor-corrector guidance modification significantly improves the entry footprint of the CEV for the lunar return mission. The performance provided by the enhanced algorithm is likely to meet the entry range requirements for the CEV.
Sizing of an Entry, Descent, and Landing System for Human Mars Exploration

(Georgia Institute of Technology, 2006-09) Christian, John A., III ; Wells, Grant William ; Lafleur, Jarret M. ; Manyapu, Kavya ; Verges, Amanda ; Lewis, Charity ; Braun, Robert D.

The human exploration of Mars presents many challenges, not least of which is the task of entry, descent, and landing (EDL). Because human-class missions are expected to have landed masses on the order of 40 to 80 metric tons, significant challenges arise that have not been seen to date in robotic missions. This study provides insight into the challenges encountered as well as potential solutions through parametric trade studies on vehicle size and mass. Aerocapture and entry-from-orbit analyses of 10 and 15 m diameter aeroshells with a lift-to-drag ratio of 0.3 or 0.5 were investigated. Results indicate that in the limit, a crew capsule used only for descent could have an initial mass as low as 20 t. For larger landed payloads, such as a 20 t surface power system, a vehicle with an initial mass on the order of 80 t may be required. In addition, no feasible EDL systems were obtained with the capability to deliver more than approximately 25 t of landed payload to the Mars surface for initial masses less than 100 t. This suggests that an aeroshell diameter of 15 m may not be sufficient for human Mars exploration.
Mars Entry, Descent, and Landing Parametric Sizing and Design Space Visualization Trades

(Georgia Institute of Technology, 2006-08) Alemany, Kristina ; Wells, Grant William ; Theisinger, John ; Clark, Ian G. ; Braun, Robert D.

Entry, descent, and landing (EDL) is a multidimensional, complex problem, which is difficult to visualize in simple plots. The purpose of this work is to develop a systematic visualization scheme that could capture Mars EDL trades as a function of a limited number of variables, such that programmatic design decisions could be effectively made with insight of the design space. Using the Mars Science Laboratory (MSL) as a basis, contour plots have been generated for key EDL figures of merit, such as maximum landed elevation and landed mass as a function of four input parameters: entry mass, entry velocity, entry flight path angle, and vehicle L/D. Additionally, sensitivity plots have been generated in an attempt to capture the effects of varying the fixed input parameters. This set of EDL visualization data has been compiled into a Mars EDL handbook to aid in pre-phase A design space exploration and decision making.
Trajectory Options for Human Mars Missions

(Georgia Institute of Technology, 2006-08) Wooster, Paul D. ; Braun, Robert D. ; Ahn, Jaemyung ; Putnam, Zachary R.

This paper explores trajectory options for the human exploration of Mars, with an emphasis on conjunction-class missions. Conjunction-class missions are characterized by short in-space durations with long surface stays, as opposed to the long in-space durations and short surface stays characteristic of opposition-class missions. Earth-Mars and Mars-Earth trajectories are presented across a series of mission opportunities and transfer times in order to explore the space of possible crew and cargo transfer trajectories. In the specific instance of crew transfer from Earth to Mars, the potential for aborting the mission without capture into Mars orbit is also of interest. As such two additional classes of trajectories are considered: free-return trajectories, where the trajectory would return the crew to Earth after a fixed period of time; and propulsive-abort trajectories, where the propulsive capability of the transfer vehicle is used to modify the trajectory during a Mars swing-by. The propulsive requirements of a trajectory, due to their associated impact on spacecraft mass, are clearly of interest in assessing trajectories for human Mars missions. Beyond the propulsive requirements, trajectory selection can have a significant impact on the entry velocity and therefore the aeroassist system requirements. The paper suggests potential constraints for entry velocities at Earth and Mars. Based upon Mars entry velocity, the 2-year period free-return abort trajectory is shown to be less desirable than previously considered for many mission opportunities.
An Evaluation of Ballute Entry Systems for Lunar Return Missions

(Georgia Institute of Technology, 2006-08) Clark, Ian G. ; Braun, Robert D. ; Theisinger, John ; Wells, Grant William

This study investigates the advantages and feasibility of using ballutes for Earth entry at lunar return velocities. Using analysis methods suitable for conceptual design and assuming a CEV type entry vehicle, multiple entry strategies were investigated. Entries that jettison the ballute after achieving low Earth orbit conditions were shown to reduce heating rates to within reusable thermal protection system limits. Deceleration was mitigated to approximately four g's when a moderate amount of lift was applied subsequent to ballute jettison. Primary ballute size drivers are the thermal limitations and areal densities of the ballute material. Performance requirements for both of those metrics were generated over a range of total ballute system masses. Lastly, preliminary investigation of a lower mass cargo variant of the CEV allowed for additional reduction of ballute system mass. However, ballute system mass as a percentage of the total entry mass was shown to be relatively independent of the entry mass.
Ultra Lightweight Ballutes for Return to Earth from the Moon

(Georgia Institute of Technology, 2006-05) Masciarelli, James P. ; Lin, John K. H. ; Ware, Joanne S. ; Rohrschneider, Reuben R. ; Braun, Robert D. ; Bartels, Robert E. ; Moses, Robert W. ; Hall, Jeffery L.

Ultra lightweight ballutes offer revolutionary mass and cost benefits along with flexibility in flight system design compared to traditional entry system technologies. Under funding provided by NASA's Exploration Systems Research & Technology program, our team was able to make progress in developing this technology through systems analysis and design, evaluation of materials and construction methods, and development of critical analysis tools. Results show that once this technology is mature, significant launch mass savings, operational simplicity, and mission robustness will be available to help carry out NASA's Vision for Space Exploration.