Maneuver simulations of flexible spacecraft by solving TPBVP

The optimal control of large angle rapid maneuvers and vibrations of a Shuttle mast reflector system is considered. The nonlinear equations of motion are formulated by using Lagrange's formula, with the mast modeled as a continuous beam. The nonlinear terms in the equations come from the coupling between the angular velocities, the modal coordinates, and the modal rates. Pontryagin's Maximum Principle is applied to the slewing problem, to derive the necessary conditions for the optimal controls, which are bounded by given saturation levels. The resulting two point boundary value problem (TPBVP) is then solved by using the quasilinearization algorithm and the method of particular solutions. In the numerical simulations, the structural parameters and the control limits from the Spacecraft Control Lab Experiment (SCOLE) are used. In the 2-D case, only the motion in the plane of an Earth orbit or the single axis slewing motion is discussed. In the 3-D slewing, the mast is modeled as a continuous beam subjected to 3-D deformations. The numerical results for both the linearized system and the nonlinear system are presented to compare the differences in their time response

Development strategy, viability, and economic distortions in developing countries

This paper presents a three-sector static model to explore the rationale for a series of institutional distortions in developing countries. The authors argue that, after World War II, motivated by a belief in the development of state-of-the-art industries as a means for nation building, the majority of developing country governments attempted to accelerate the growth of advanced capital-intensive industries. However, since developing countries are relatively rich in labor or natural resource endowments but not in capital endowment, advanced capital-intensive industries were not adapted to the endowment structures of these developing countries at the time. Enterprises in those industries were non-viable in open, competitive markets and could not survive without government subsidization or protection. The model shows that, in order to mobilize resources into the capital-intensive, advanced sectors, it is necessary for governments to use distortionary policies such as taxes and subsidies, distortions of factor prices, directive allocation of resources, and nationalization of enterprises. Such distortions enable developing countries to set up advanced, capital-intensive industries in the early stage of their development. However, they also tend to suppress incentives, misallocate resources, and make the economy inefficient.Economic Theory&Research,Debt Markets,Emerging Markets,Public Sector Corruption&Anticorruption Measures,Currencies and Exchange Rates

Minimum time attitude slewing maneuvers of a rigid spacecraft

The problems of large-angle attitude maneuvers of a spacecraft have gained much consideration in recent years. The configurations of the spacecraft considered are: completely rigid, a combination of rigid and flexible parts, or gyrostat-type systems. The performance indices usually include minimum torque integration, power criterion, and frequency-shaped cost functionals. The minimum time slewing problem of a rigid spacecraft was examined. Optimal control theory (Maximum Principal) was applied to the slewing motion of a general rigid spacecraft. Control torque about all three axes was computed. The equations for the system are composed of the Euler dynamical equations in the spacecraft body axes and the quaternion kinematical equation. By introducing the costates for the quaternion and the angular velocity, the Hamiltonian of the system can be formed and the optimal control obtained. Finally the methods are applied to the SCOLE slewing motion. The control variables include three control moments on the Shuttle and two control forces on the reflector. Numerical results are discussed