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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: 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: 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: National Aeronautics and Space Administration (NASA) Publisher: Createspace Independent Publishing Platform ISBN: 9781722410049 Category : Languages : en Pages : 64
Book Description
The problem of minimization of fuel consumption during the atmospheric portion of an aeroassisted, orbital transfer with plane change is addressed. The complete mission has required three characteristic velocities, a deorbit impulse at high earth orbit (HEO), a boost impulse at the atmospheric exit, and a reorbit impulse at low earth orbit (LEO). A performance index has been formulated as the sum of these three impulses. Application of optimal control principles has led to a nonlinear, two-point, boundary value problem which was solved by using a multiple shooting algorithm. The strategy for the atmospheric portion of the minimum-fuel transfer is to start initially with the maximum positive lift in order to recover from the downward plunge, and then to fly with a gradually decreasing lift such that the vehicle skips out of the atmosphere with a flight path angle near zero degrees. Naidu, Desineni Subbaramaiah and Hibey, Joseph L. Unspecified Center...
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: Eugene A. Smith Publisher: ISBN: Category : Languages : en Pages : 93
Book Description
Minimum fuel continuous low thrust orbit transfer is an optimal control problem which requires the application of iterative numerical methods to solve the resulting two point boundary value problem. A combination gradient- neighboring extremal algorithm gives accurate results when both the initial and terminal orbits are coplanar. These results are then used to extend the problem to include out-of-plane transfers between orbits of widely varying inclination. Control histories, in terms of thrust direction, are plotted as a function of time for both coplanar and non-coplanar transfers. Steering programs for coplanar transfers are characterized by a rapid thrust reversal which is dependent on eccentricity for the time of its occurrence. In the latter case, out-of-plane thrusting is primarily a function of the inclination change between orbits. On the basis of these results, the particular numerical approach used provides an effective method for generating optimal low thrust orbital transfer guidance.
Author: Begum Senses
Author: Begum Senses
Author: Lawrence E. Halbach
Author: National Aeronautics and Space Administration (NASA)
Author: Jerry L. Mrozek (CAPT, USAF.)
Author: 
Author: Karl E. Jensen
Author: Eugene A. Smith
Author: 
Author: Peter Alexander Bidian
Author: