Collision-avoidance assured path-planning for Starlight interferometer
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formation flying collision avoidance↗
Engineering topics
Singh, G.
Publications and source records attributed to Singh, G..
StarLight - formation flying control architecture
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distributed spacecraft control formation flying ar↗
Autonomous Guidance and Control Design for Hazard Avoidance Aand Safe Landing on Mars
To ensure successful future Mars landing missions, the lander must be capable of detecting hazards in the landing zone and maneuvering to a new and safe site.
guidance and control hazard avoidance autonomy saf↗
Autonomous path-planning for formation flying-applications
The paper presents a solution to the optimal formation path-planning problem where the formation reconfigurations are required subject to collision avoidance and resource limitation contraints.
formation flying collision-avoidance path-planning↗
Optimal collision avoidance guidance for formation-flying applications
Several proposed space science missions require deployment of a number of spacecraft to form a single functional unit or a formation flying spacecraft. There are many applications of a formation flying spacecraft; variable baseline optical space interferometry is one of them.
collision avoidance path-planning formation-flying↗
Post-flight attitude reconstruction for the Shuttle Topography Mission
The Shuttle Radar Topography Mission is the first mission to provide high accuracy near-global topographic coverage of the Earth's land surface using a long-baseline interferometry approach.
attitude reconstruction interferometry mast struct↗
A centralized optimal controller for formation flying spacecraft
Formation flying spacecraft is emerging as an enabling technology for the discovery of new type of science for the emerging NASA deep space and Earth science missions.
interferometers↗
Characterization of Passive Dynamic Stability of a Microwave Sail
The idea of converting electromagnetic energy into mechanical energy is not new.
Stability Microwaves Dynamics↗
Galileo Attitude Determination: Experiences with a Rotating Star Scanner
The Galileo experience with a rotating star scanner is discussed in terms of problems encountered in flight, solutions implemented, and lessons learned. An overview of the Galileo project and the attitude and articulation control subsystem is given and the star scanner hardware and relevant software algorithms are detailed. The star scanner is the sole source of inertial attitude reference for this spacecraft. Problem symptoms observed in flight are discussed in terms of effects on spacecraft performance and safety. Sources of thse problems include contributions from flight software idiosyncrasies and inadequate validation of the ground procedures used to identify target stars for use by the autonomous on-board star identification algorithm. Problem fixes (some already implemented and some only proposed) are discussed. A general conclusion is drawn regarding the inherent difficulty of performing simulation tests to validate algorithms which are highly sensitive to external inputs of statistically 'rare' events.
Merken, L.↗
Time-optical spinup maneuvers of flexible spacecraft
Attitude controllers for spacecraft have been based on the assumption that the bodies being controlled are rigid. Future spacecraft, however, may be quite flexible. Many applications require spinning up/down these vehicles. In this work the minimum time control of these maneuvers is considered. The time-optimal control is shown to possess an important symmetry property. Taking advantage of this property, the necessary and sufficient conditions for optimality are transformed into a system of nonlinear algebraic equations in the control switching times during one half of the maneuver, the maneuver time, and the costates at the mid-maneuver time. These equations can be solved using a homotopy approach. Control spillover measures are introduced and upper bounds on these measures are obtained. For a special case these upper bounds can be expressed in closed form for an infinite dimensional evaluation model. Rotational stiffening effects are ignored in the optimal control analysis. Based on a heuristic argument a simple condition is given which justifies the omission of these nonlinear effects. This condition is validated by numerical simulation.
Singh, G.↗
Use of microwaves to improve nutritional value of soybeans for future space inhabitants
Whole soybeans from four different varieties at different moisture contents were microwaved for varying times to determine the conditions for maximum destruction of trypsin inhibitor and lipoxygenase activities, and optimal growth of chicks. Microwaving 150 gm samples of soybeans (at 14 to 28% moisture) for 1.5 min was found optimal for reduction of trypsin inhibitor and lipoxygenase activities. Microwaving 1 kgm samples of soybeans for 9 minutes destroyed 82% of the trypsin inhibitor activity and gave optimal chick growth. It should be pointed out that the microwaving time would vary according to the weight of the sample and the power of the microwave oven. The microwave oven used in the above experiments was rated at 650 watts 2450 MHz.
Singh, G.↗
Stability analysis of the discrete-data Large-Space-Telescope system
This paper considers the application of the discrete describing function to the stability analysis of the Large-Space Telescope (LST) system. An analytical model of the CMG gimbal friction is derived, which is then used to arrive at a closed-form analytical expression for the discrete describing function of the nonlinearity. The analysis is used for the study of the fine-pointing stability of the LST vehicle. Simulation results corroborate the conclusions from the analytical analysis.
Kuo, B. C.↗
Research study on stabilization and control. Modern sampled-data control theory: Stability analysis of the low cost large space telescope system
The pointing stability of the low-cost large space telescope (LST) system was investigated. The low-cost LST is characterized by the use of reaction wheels for the generation of control torques. Because of the critical requirement on the pointing accuracy of the LST, the nonlinear frictional characteristics of the bearings of the reaction wheels were studied which can cause limit cycles in a closed-loop system. Another possible source of pointing error in the LST is due to the effect of quantization and sensor noise. Since the LST is a digital system, digital to analog and analog to digital converters and sensors for positional and rate feedbacks were used. Sensor noise and amplitude quantization causes pointing error in the LST and, in addition, quantization is a nonlinear phenomenon which can cause self-sustained oscillations in the closed-loop system. The dynamic modeling of the single-axis LST is described, and several methods of evaluating the attitude error of the digital LST due to quantization and noise inputs are given.
Kuo, B. C.↗
Limit cycle analysis of large space telescope with CMG nonlinearity
The existence and characteristics of self-sustained oscillations were studied in the Large Space Telescope (LST) system due to the presence of nonlinear gimbal friction in the control moment gyroscopes (CMG's). A continuous data single-axis model of the LST is considered. A solid friction model is used to represent CMG gimbal friction. A rigorous mathematical model is derived for use in a continuous describing function analysis. Conditions for self-sustained oscillations are then determined.
Seltzer, S. M.↗
Research study on stabilization and control. Modern sampled-date control theory. Stability analysis of the low cost large space telescope system
A mathematical model employing Fourier series is used to show quantization and reaction wheel friction nonlinearity in a telescope system for use in space. Block diagrams are used to illustrate the system. A discrete describing function of a quantizer also is given, and input and output signal waveforms, with illustrative examples, are shown.
Kuo, B. C.↗
Research study on stabilization and control: Modern sampled-data control theory. Design of the large space telescope system
Conditions of self-sustained oscillations in a two-axis model of the nonlinear LST system are studied. The describing function of the CMG frictional nonlinearity of the LST system is used for the analysis, as well as continuous-data and discrete-data models of the simplified LST control system. A numerical-iterative method is described for the analysis of the two-axis system. Approximation methods and the direct plotting of the stability equation are implemented in the study. It is shown that although the dynamics of the two axes are identical, the amplitudes of self-sustained oscillations in the two axes may in principle be different. Analysis shows that the LST systems are of equal amplitudes but with 180-degree phase shift.
Kuo, B. C.↗
Research study on stabilization and control modern sampled-data control theory. Design of the Large Space Telescope system
The numerical technique is applied to the prediction of self-sustained oscillations in a two-axis model of the nonlinear system with sampled data. The sampled-data two-axis LST system model, and its stability equation are analyzed along with the exact solution of the stability equation by numerical-iterative techniques.
Kuo, B. C.↗
Research study on stabilization and control modern sampled-data control theory
The methods of continuous and discrete describing function analysis were applied to predicting the existence of self-sustained oscillations in the single-axis model of the large space telescope system with nonlinear control moment gyroscope friction characteristics. It is shown that the stability equations may be solved by a numerical-iterative technique using the describing function analysis, instead of the usual graphical methods. The numerical method is found to be effective in leading to a convergent solution rapidly, with an appropriate guess of the initial condition.
Kuo, B. C.↗