On reduction of longest accessibility gap in LEO sun-synchronous satellite missions

Lat. Am. j. solids struct.

Mirzaei

2017

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This paper focuses on robust optimal adaptive control strategy to deal with tracking problem of a quadrotor unmanned aerial vehicle (UAV) in presence of parametric uncertainties, actuator amplitude constraints, and unknown time-varying external disturbances. First, Lyapunov-based indirect adaptive controller optimized by particle swarm optimization (PSO) is developed for multi-input multi-output (MIMO) nonlinear quadrotor to prevent input constraints violation, and then disturbance observer-based control (DOBC) technique is aggregated with the control system to attenuate the effects of disturbance generated by an exogenous system. The performance of synthesis control method is evaluated by a new performance index function in time-domain, and the stability analysis is carried out using Lyapunov theory. Finally, illustrative numerical simulations are conducted to demonstrate the effectiveness of the presented approach in altitude and attitude tracking under several conditions, including large time-varying uncertainty, exogenous disturbance, and control input constraints.

Section: Introductionmentioning

confidence: 99%

Robust Optimal Adaptive Trajectory Tracking Control of Quadrotor Helicopter

Lat. Am. j. solids struct.

Mirzaei

2017

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“…Thus, it is convenient to consider only dominant J 2 perturbing geopotential. As discussed in our previous work, 29 for J 2 perturbing geopotential, an elegant form of Lagrange planetary equations is obtained, given in equation ( 2)…”

Section: Analytical Methods Of Access Pattern Determinationmentioning

confidence: 99%

Improving in-orbit responsiveness of low earth orbit sun-synchronous satellites by selection of ground segment location

Proceedings of the Institution of Mechanical Engineers, Part G:

Khamseh

2012

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Responsiveness is a key requirement for spaceborne systems to sustain competitive advantage over non-spaceborne systems. For an operational satellite, in-orbit responsiveness is defined as the agility of the satellite to respond to a given demand. In this article, the average wait time to pick up user demand from the ground segment is adopted as the metric to evaluate the effect of ground segment location on in-orbit responsiveness of low earth orbit sun-synchronous satellites. The average wait time metric depends on the pattern of ground segment access to satellite and also on distribution of user demands. An analytical method is employed to determine pattern of ground segment access to satellite. Distribution of user demands in time domain is modeled by the means of cumulative distribution function concept. Monte Carlo simulations are adopted to capture inherent uncertainty in distribution and total volume of user demands. Based on average wait time metric, ground segment locations which improve in-orbit responsive of satellite are found. In order to show feasibility of our proposed approach, a case study is adopted and improvement of average wait time metric depending on ground segment location is demonstrated. Also, average wait time metric for various ground segment locations is given for illustration.

“…To take account of this peculiar access patterns, in our previous work, two accessbased metrics were developed, namely total accessibility duration (TAD) and longest accessibility gap (LAG). 1 LAG was comprehensively discussed in Bonyan Khamseh and Navabi, 2 and here TAD is treated. Accessibility gap and accessibility duration are schematically shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

“…Typical pattern of access to a LEO sunsynchronous satellite. 2 inherent dependency of TAD formulation to date. Then, in ''Perturbative method of TAD determination'', the perturbative method of TAD determination is discussed and formulas for TAD determination are developed in ''Development of surrogate models''.…”

Section: Introductionmentioning

confidence: 99%

Simple surrogate models to determine total accessibility duration of low Earth orbit sunsynchronous satellites

Khamseh

Proceedings of the Institution of Mechanical Engineers, Part G:

2012

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Short and infrequent access events are inherent characteristics of low Earth orbit sunsynchronous satellites. Furthermore, for such satellites, distribution pattern of access events varies significantly in time. Thus, determination of the metric of total accessibility duration in a given time interval has been a challenge in the field of low Earth orbit satellite systems engineering. In this article, for zero and conventional non-zero minimum elevation angles, surrogate models were developed to determine total accessibility duration of low Earth orbit satellites, based on orbital altitude of the satellite and latitude of the ground segment. For this purpose, concept of repeatability cycle was employed to achieve total accessibility duration in a time-independent manner. Then, a perturbative propagation model was presented to determine pattern of accessibility events and quantify total accessibility duration metric. In order to account for non-zero minimum elevation angles, two distinct approaches were adopted. In the first approach, four modification factors were introduced to modify the surrogate model for zero elevation angle to account for conventional non-zero minimum elevation angles. In the second approach, a dedicated surrogate model was developed to directly determine total accessibility duration for conventional non-zero minimum elevation angles. Numerous examples are examined to verify fidelity of our two proposed approaches. Due to their simplicity, the surrogate models given in this article eliminate the need for professional staff to determine metric of total accessibility duration. The advantage is that considerable saving in required initial staff cost and schedule can be realized, especially in early mission design phases.