In this paper Deprit's variables are used to describe the Hamiltonian equations for attitude motions of a gyrostat satellite spinning about arbitrarily body-fixed axes. The Hamiltonian equations for the attitude motions of the gyrostat satellite in terms of the Deprit's variables and under small viscous damping and nonautonomous perturbations are suitable for the employment of the Melnikov's integral. The torque-free homoclinic orbits to the symmetric Kelvin gyrostat are derived by means of the elliptic function integral theory. With the help of residue theory of complex functions, the Melnikov's integral is utilized to analytically study the criterion for chaotic oscillations of the attitude motions of the symmetric Kelvin gyrostat under small, damping and periodic external disturbing torques. The Melnikov's integral yields an analytical criterion for the chaotic oscillations of the attitude motions in the form of an inequality that gives a necessary condition for chaotic dynamics in terms of the physical parameters. The dependence of the onset of homoclinic orbits on quantities such as body shapes, the initial conditions of the angular velocities or the two constants of motions of the torque-free gyrostat satellite is investigated in details. The dependence of the onset of chaos on quantities such as the amplitudes of the external excitation and the damping coefficients' matrix is discussed. The bifurcation curves based upon the Melnikov's integral are computed by using the combined parameters versus the frequency of the external excitation. The theoretical criterion agrees with the result of the numerical simulation of the gyrostat satellite by using the fourth-order Runge-Kutta integration algorithm. The numerical solutions show that the motions of the perturbed symmetric gyrostat satellite possess a lot of "random" characteristic associated with a nonperiodic solution.

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X-Sat is a micro-satellite project with the objective to design, build, test and operate Singapore's first domestic satellite. The mission's main aim is to provide imaging capability for earth observation and environmental monitoring over Singapore and the South East Asian region with daily coverage and downlink of the acquired imagery within the same orbit. Secondary objectives are satellite-based advanced data acquisition and messaging over the Indian and Pacific Ocean as well as high performance fault tolerant on-board data processing using commercial off-the-shelf components. This flagship project of the Centre for Research in Satellite Technology was started officially in 2002 and seeks to foster national and international collaborations among various educational, research and commercial partners. At the time of publication the development and testing of the engineering model is almost completed, while the piggyback launch is scheduled for 2007.

A dual aperture‐coupled rectangular microstrip patch antenna with two superstrate layers is designed. This kind of antenna has the advantages of high gain, wide band, and dual polarization. Details of the experimental results are presented and discussed. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 282–284 1999