Master's Projects

Series

Master's Projects

Permanent Link

https://hdl.handle.net/1853/71003

Series Type

Publication Series

Full item page

Publication Search Results

Now showing 1 - 10 of 40

Low-Thrust Trajectory Optimization Tool to Assess Options for Near-Earth Asteroid Deflection

(Georgia Institute of Technology, 2007-12-01) Stahl, Benjamin Andrew

In the past decade, the scientific community has become more interested in Near Earth Objects (NEOs) and the threat they pose to existence of life on this planet. The recent trend in NEO deflection technique research has been toward “slow push” techniques in order to absolve the need for sending nuclear weapons into space. A software tool was developed to assist in design and performance testing of various low-thrust deflection methods. The tool features an n-body high fidelity long term orbit propagator that allows for deflection mechanism forces to be directly applied through the equations of motion. The propagator utilizes DE405 ephemeris data for the acting bodies and was validated through comparison with JPL’s HORIZONS database. A hybrid optimization algorithm featuring a genetic algorithm global search and a conjugate direction local search was also developed to optimize the thrust direction versus time for a given deflection technique. The optimizer is applicable for many different missions and objectives, and is tested with several missions designed to maximize NEO close approach miss distance.
Hypersonic Entry Aeroshell Shape Optimization

(Georgia Institute of Technology, 2007-12-01) Theisinger, John E.

Several different approaches to shape optimization are explored to identify hypersonic aeroshell shapes that will increase landed mass capability by maximizing drag-area for a specified lift-to-drag ratio. The most basic approach manipulates standard parameters associated with analytic aeroshell shapes like the sphere-cone and ellipsled. More general approaches manipulate the control points of a spline curve or surface. The parametric polynomial formulations of the Bezier and B-spline curves and surfaces are employed due to their desirable properties in shape design. Hypersonic aerodynamic analyses are carried out using Newtonian flow theory panel methods. An integrated optimization environment is created, and a variety of optimization methods are applied. In addition to a lift-to-drag ratio constraint, size constraints are imposed on the aeroshell, as determined by payload volume requirements and launch vehicle shroud size restrictions. Static stability and center-of gravity placement required to achieve hypersonic trim are also considered during optimization. An example case is presented based on the aeroshell for the Mars Science Laboratory mission.
Space Shuttle Solid Rocket Booster Control Limitations Due to Failure of an Hydraulic Power Unit

(Georgia Institute of Technology, 2007-11-21) Kranzusch, Kara M.

The Space Shuttle solid rocket boosters (SRBs) each have two nozzle actuators to provide thrust vector control (TVC). Two hydraulic power units (HPUs) provide hydraulic pressure to drive the actuators and are capable of driving both gimbals simultaneously at 5º/s. One HPU, however, is only designed to drive both gimbals simultaneously at a combined rate of 6º/s. Reduced gimbal rate capability due to failure of an HPU can limit the gimbal’s ability to keep up with commands and the development of large command-position deltas could cause loss of control of the actuator. Due to SRB thrust authority during the Shuttle’s first stage, loss of control of an SRB TVC could result in loss of the vehicle. To study the effect of a failed HPU during nominal ascent profiles, an SRB actuator was modeled in SIMULINK and the gimbal drive rate was limited to simulate the failure. The maximum resulting command-position deltas were calculated to determine control limitations. The required gimbal rate summation limit to cause loss of control of an SRB actuator in response to an HPU failure during nominal ascent demands is also estimated. Through this analysis, large margins are demonstrated against this failure scenario. The availability and feasibility of an operational response are discussed.
Statistical Reconstruction of Mars Entry, Descent, and Landing Trajectories and Atmospheric Profiles

(Georgia Institute of Technology, 2007-04-27) Christian, John Allen

Accurate post-flight reconstruction of a vehicle’s trajectory during entry into a planetary atmosphere can produce a wide array of valuable information. The data collected through the reconstruction of entry, descent, and landing (EDL) system performance enables the quantification of performance margins for future systems. Beyond the engineering knowledge gained through trajectory reconstruction, the results may also be used by planetary scientists to generate an accurate atmospheric profile. A computer tool was developed to facilitate the rapid analysis of data gathered during entry. Emphasis was placed on making the tool flexible and capable of easily incorporating different types of data. These data are used to provide an accurate reconstruction through the use of an Extended Kalman Filter (EKF). In its present form, the filter propagates the mean state forward using a three degree-of-freedom dynamic model and is capable of handling data from accelerometers and altimeters. The tool is validated against previous trajectory and atmosphere reconstructions that were performed for the Mars Pathfinder mission.
Optimal trajectories for soft landing on asteroids

(Georgia Institute of Technology, 2006-12-15) Lantoine, Gregory

Robotic exploration of asteroids has been identified by NASA as a major long-term goal. Central to many asteroid missions is a precise soft landing to enable surface exploration or exploitation. This paper describes a technique for computing optimal autonomous controlled trajectories for soft landing in an irregular gravity field of a rotating asteroid. We will first discuss the complexity of the forces that act on the spacecraft during a landing and how we can model them. Then, we will present the numerical method used to solve the optimal control problem, and typical results are shown on case studies at asteroids Vesta and Golevka. In each example, we will identify the best mission design scenarios, as well as some operational difficulties. Finally, we will investigate sensitivity to parameter uncertainties and the implementation of a real-time feedback controller to increase landing accuracy.
An Evaluation of Ballute Entry Systems for Lunar Return Missions

(Georgia Institute of Technology, 2006-05-07) Clark, Ian G.

A study was undertaken to assess the advantages and feasibility of using ballutes for Earth entry at lunar return velocities. Using analysis methods suitable for conceptual design, multiple entry strategies were investigated. Entries that jettison the ballute after achieving orbit were shown to reduce heating rates to within reusable thermal protection system limits and deceleration was mitigated to approximately four g’s when a moderate amount of lift was applied post-jettison. Ballute size drivers were demonstrated to be 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.
Mars Entry, Descent and Landing Parametric Trades

(Georgia Institute of Technology, 2006-05-01) Wells, Grant

The purpose of this investigation is to begin forming a dataset to be the basis of a Mars entry, descent and landing mission design handbook for planetary probes. The premise of the project is that Mars entry, descent and landing can be parameterized with five variables: (1) entry mass, (2) entry velocity, (3) entry flight path angle, (4) vehicle aeroshell diameter, and (5) vertical lift-to-drag ratio. For combinations of these input parameters, the following trajectory information will be determined: peak deceleration, peak heat rate, heat load, and the altitude at which Mach 2 is reached (for parachute deployment).
Performance Evaluation of a Side Mounted Shuttle Derived Heavy Lift Launch Vehicle for Lunar Exploration

(Georgia Institute of Technology, 2006-05-01) Thompson, Robert W.

The NASA Exploration Systems Architecture Study (ESAS) produced a transportation architecture for returning humans to the moon affordably and safely. ESAS determined that the best lunar exploration strategy was to separate the launch of crew from the launch of cargo, thereby requiring two launches per lunar mission. An alternate concept for the cargo launch vehicle is a side mounted Shuttle-derived heavy lift launch. This configuration is similar to previously studied concepts, except engines and structure have been added to the External Tank (ET), making it a complete first stage. The upper stage is mounted on the side of the first stage, much like the Shuttle orbiter is mounted on the side of the ET. Like the Shuttle, solid rocket boosters (SRBs) are also used. This configuration has several performance and operational benefits over an in-line heavy lift launch vehicle. According to the ESAS report, side mount configurations were not considered to be among the most promising configurations, and were not carried forward for further consideration within architectural options. The performance of this launch vehicle is independently analyzed, using multidisciplinary analysis techniques. Methods and tools used include launch trajectory optimization with POST, vehicle aerodynamic analysis using APAS, and weights and sizing using historically based estimating relationships. Principal trade studies performed include first and second stage propulsion (number of engines and engine type), solid rocket booster size (four versus five segment), and staging ∆V. The vehicle design that best meets the requirements for space exploration (lunar and future missions) is presented.
A Scalable Orbital Propellant Depot Design

(Georgia Institute of Technology, 2006-05-01) Street, David

This paper describes the design and features of a Scalable Orbital Propellant Depot Design tool. The purpose of the tool is to enable others to easily test the effectiveness of adding a propellant depot to an exploration architecture. Several options are available including zero boil-off technology, usable propellant and depot geometry. It is assumed that the depot is refillable with a total service life of 10 years and resides in low earth orbit. Examples of depots created with the tool are shown. Application to existing exploration architectures is also discussed.
Entry System Design of the Mars Gravity Biosatellite

(Georgia Institute of Technology, 2006-04-19) Francis, Scott

The Mars Gravity Biosatellite will be launched to low Earth orbit and will study the effects of partial gravity on mammalian physiology. The entry vehicle will return 15 live mice to the Earth’s surface from low Earth orbit, landing in the Woomera Prohibited Area in central South Australia. This study establishes a baseline for the entry, descent, and landing system through the comparison of various concepts. The Discoverer capsule from the military’s Corona program of the 1950’s and 60’s is chosen over other concepts as the baseline aeroshell after an analysis of static stability and payload requirements for this mission. A nominal trajectory is developed based on science requirements, the safety of the mice, and payload recovery requirements. A sensitivity study is performed on the entry trajectory to determine the effects various parameters have on the nominal entry and a Monte Carlo dispersion analysis is used to establish a 3-σ landing ellipse, which fits within the boundaries of the Woomera Prohibited Area. A discussion of potential de-orbit propulsive devices is given in relation to the required de-orbit ∆V. A 16 m parachute is chosen as the baseline due to the resulting 4.8 m/s ground impact velocity and a crushable aluminum foam is chosen as a means to attenuate the shock of ground impact.