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Author: Lawrence E. Halbach Publisher: ISBN: 9781423532118 Category : Languages : en Pages : 92
Book Description
This thesis studies the fuel optimal periodic reboost profile required to maintain a spacecraft experiencing drag in low-earth-orbit (LEO). Recent advances in computational optimal control theory are employed, along with a Legendre-Gauss-Lobatto Pseudospectral collocation code developed at the Naval Postgraduate School, to solve the problem. Solutions obtained by this method are compared against a previous study. Key issues were checking the optimality of the solutions by way of the necessary conditions and the behavior of the solution to changes in the thruster size. The results confirmed Jensen's findings of propellant savings of one to five percent when compared against a middle altitude Forced Keplerian Trajectory (FKT). Larger savings are predicted if compared against a finite-burn Hohmann transfer with drag. The costates estimates compared favorably against necessary conditions of Pontryagin's Minimum Principle. Analysis of the switching flinction yielded periods of thrust-modulated arcs. The optimal thrust profile appears to be a thrust- modulated burn to raise the orbit followed by an orbital decay and a terminating thrust-modulated arc. For a sufficiently low thrust-control authority, the switching structure includes a maximum thrust arc. Indirect optimization techniques to confirm these findings were unsuccessful.
Author: Lawrence E. Halbach Publisher: ISBN: 9781423532118 Category : Languages : en Pages : 92
Book Description
This thesis studies the fuel optimal periodic reboost profile required to maintain a spacecraft experiencing drag in low-earth-orbit (LEO). Recent advances in computational optimal control theory are employed, along with a Legendre-Gauss-Lobatto Pseudospectral collocation code developed at the Naval Postgraduate School, to solve the problem. Solutions obtained by this method are compared against a previous study. Key issues were checking the optimality of the solutions by way of the necessary conditions and the behavior of the solution to changes in the thruster size. The results confirmed Jensen's findings of propellant savings of one to five percent when compared against a middle altitude Forced Keplerian Trajectory (FKT). Larger savings are predicted if compared against a finite-burn Hohmann transfer with drag. The costates estimates compared favorably against necessary conditions of Pontryagin's Minimum Principle. Analysis of the switching flinction yielded periods of thrust-modulated arcs. The optimal thrust profile appears to be a thrust- modulated burn to raise the orbit followed by an orbital decay and a terminating thrust-modulated arc. For a sufficiently low thrust-control authority, the switching structure includes a maximum thrust arc. Indirect optimization techniques to confirm these findings were unsuccessful.
Author: Karl E. Jensen Publisher: ISBN: 9781423559764 Category : Languages : en Pages : 127
Book Description
First-order solutions indicate that a forced Keplerian trajectory (FKT) obtained by thrust-drag cancellation is as fuel-efficient as a Hohmann transfer. Further analysis has shown that the FKT is not Mayer-optimal. Therefore there must exist another trajectory that matches or exceeds the efficiency of the Hohmann transfer. The application of this result to the fuel- optimal orbit maintenance problem implies that periodic reboosts must be more efficient than an WT profile. This research begins with the formulation of an optimal periodic control (OPC) problem to determine the minimum fuel-reboost strategy. The problem is numerically solved by a spectral collocation method. The optimization code is further modified to increase accuracy and reduce sensitivity to initial guesses. The results of this effort identified a trajectory for a sample satellite that was 3.5% more efficient than an ideal impulsive Hohmann transfer over the same period of time. From the optimal code, a maximum thruster size is also identifiable for a set of initial conditions. The optimal trajectory can save as much as 10% of the propellant budget when compared to finite-bum Hohmann transfers.
Author: Begum Senses Publisher: ISBN: Category : Languages : en Pages :
Book Description
ABSTRACT: In this study, minimum fuel solutions to finite thrust noncoplanar aeroassisted orbital transfers of a small spacecraft between two low-Earth orbits are found using General Pseudospectral Optimal Control Software (GPOPS) which applies an hp-adaptive pseudospectral method. Optimal trajectories, and final mass ratios of the small spacecraft that are obtained subject to various inclination changes, heating rate constraints, and number of atmospheric passes are compared. It is observed that, fuel consumption is proportional to the inclination change, on the other hand, it is inversely proportional to the heating rate constraint. Furthermore, for the cases where the heating rate is not constrained, the number of atmospheric passes does not affect the fuel consumption. For the cases where the heating rate is constrained, increasing number of atmospheric passes, however, decreases fuel consumption.
Author: Paul A. Gardner Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
With the requirement for a spacecraft to maintain an orbital altitude band, a simple energy balance algorithm has been developed using a combination of radial distance and spacecraft specific energy for fixed-vector thruster control. While each trajectory produces a unique band, initial attempts at producing a pre-specified band have been unsuccessful. It is theorized that a certain radial bandwidth would correspond to a specific set of control parameters, and that by creating maps of the relationship between the two for various spacecraft configurations a method of maintaining the pre-specified band could be found. This thesis studies variations in spacecraft configurations and finds dependence of orbital bandwidth on thrust-to-drag ratio and ballistic coefficient. Also, within certain ranges of control parameters, multiple trajectories produce equivalent radial bands. Analysis shows that all single- burn trajectories are characterized by similar efficiencies, and are less efficient than a Forced Keplerian Trajectory (FKT).
Author: John O'Gorman Publisher: ISBN: Category : Artificial satellites Languages : en Pages : 45
Book Description
"Ever since the launch of Sputnik in 1957, humans have put over 40,000 pieces of debris into orbit around the Earth. In particular, most launches and debris tends to go to either Low Earth Orbit (LEO), or Geosynchronous Earth Orbit (GEO). While GEO has some regulations on its use, there are limited regulations for the use of LEO. Accumulated debris in LEO jeopardizes the future utility of space. So far, various measures for the mitigation and management of debris in LEO have been proposed. This paper looks to establish a baseline cost of clean space in LEO against which other debris management policies can be compared. By launching to MEO instead of LEO, an upper bound cost of $22.15 million would needed between now and 2050, by which time about one third of all the debris pieces in LEO would have decayed into the upper atmosphere. Though such a policy is not likely to be implemented, and downright impossible to carry out for microsatellites, the cost study should serve as a baseline for other proposed policies to keep LEO relatively clear of debris and safe for continued human use."--Abstract.
Author: Lawrence E. Halbach
Author: Lawrence E. Halbach
Author: Karl E. Jensen
Author: Mark S. Wilsey
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Author: Begum Senses
Author: 
Author: Paul A. Gardner
Author: 
Author: John O'Gorman
Author: Roger E. Diehl