The GYROLITE: Is it Unstable?

A new derivation of the GYROLITE stability criterion is presented. It is confirmed that, for the satellite to have a stable attitude, the spinning part must have a favorable inertia ratio.     

Analysis of Detection Probability for the Acoustooptic Receiver

A numerical method is described for analyzing the performance of an acoustooptic receiver. The method provides output waveforms, probability density functions for samples of the output, and detection probabilities for output samples. The approach is general in that input pulse envelope shapes, pulse offset frequencies, and output rilter magnitude responses are arbitrary. The basic analysis is also independent of the shape of the optical beam and of the photodiode windows.     

Wide angle X-ray optics for use in astronomy

Recently there was a suggestion in the literature to apply the principle of the lobster-eye to X-ray astronomy imaging (J.R.P. Angel, Ap. J. 233, 364, 1979). Our own suggestion for a wide angle X-ray telescope made earlier (W.K.H. Schmidt, Nucl. Instr. Meth.127, 285, 1975) is very similar to the above one. It consists of one or two sets of plane mirrors used in a grazing incidence configuration. The advantages of this type of X-ray optics over other systems for particular astronomical observations will be discussed.     

Stabilization of Precision Electrooptical Pointing and Tracking Systems

This paper presents the pointing vector and angular rate relationshipsfor various optical elements as well as techniques developed forestablishing comprehensive analytical models of precision electroopticalstabilization systems. Since the performance of such systemsmay be critically dependent on the disturbance environment and theintegrity of the associated mechanism, these factors are also examinedin detail.     

Switchless Control Strategies for Minimum Time Frequency Transitions in Phase-Locked Loops

The problem of minimum time frequency transitions in phase-locked loops with both phase and frequency controls applied is investigated using Pontryagin's maximum principle. Typically, a type II secondorder loop with a damping ratio of 0.707 subjected to a step change in the frequency of its input signal is considered and switchless control strategies that force the transients in the loop to settle down in minimum time are obtained.     

A Nutation Damper for a Dual-Spin Spacecraft

This paper is concerned with a high-performance nutation damper for use in dual-spin spacecraft. The damper described here makes use of a wheel of uniform mass distribution. The wheel experiences torques which are produced by inertial forces. Damping and restoring (spring) torques are provided by means of a torsional arrangement built around the center of the wheel. The performance characteristics of the above nutation damper are evaluated by considering the small astronomy satellite (SAS-A) spacecraft parameters, and the results for an optimum design of the damper are presented. Finally, the result for the optimum performance is checked with the help of an approximate analysis.     

Atmospheric Error in Range and Range-Rate Measurements between a Ground Station and an Artificial Satellite

The propagation errors caused by the atmosphere are investigated in order to find out the causes of the observed errors in range and range-rate measurements between a ground station and an artificial satellite. The calculations show that the observed errors are mostly caused by the measuring instruments. The propagation errors are mainly caused by increases, decreases, or fluctuations of the refractive index of the atmosphere, and the errors caused by the refraction of the propagation path are about 10 percent of the errors caused by the decrease of the propagation velocity. The tropospheric range errors are less than 150 meters and are approximately expressed by a cotangent function, and they are reduced by about 90 percent through the use of monthly average refractivity profiles of the troposphere. The ionospheric errors are usually negligible at centimeter radio waves (less than 10 cm), and even at decimeter waves or meter waves almost all errors can be removed by the use of two different frequencies on the down-link so that the range can be made independent of frequency.     

Radioisotope-powered free-piston Stirling engine for space applications

The paper presents a preliminary conceptual design of a 2kW(e) autonomous power system consisting of a radioisotopic heat source, free-piston Stirling engine, reciprocating induction generator and a space radiator. The proposed design features a direct thermal interfacing of the Pu-238 heat source with the Stirling engine head, low heat losses during normal operation, and provides an auxiliary/emergency cooling system in the case of the engine failure of stopping. The Stirling engine is of the free-displacer, free-piston type invented by Beale and uses helium as the working fluid. The engine piston is integrated with the armature of a simple linear alternator which is used for electric generation. Waste heat is rejected by a four-finned space radiator sized for a geosynchronous orbit. Specific power and efficiency of the Stirling isotope power system are compared with the present and predicted performance of other power conversion systems suitable for the same power range.     

Angular Velocity Measurement Using Rate Gyros in a Spinning Vehicle

It is shown that when the gyro spin vector is in opposition to the spin vector of the vehicle, the output differential equation of the gyro becomes unstable for large vehicle spin values. When the gyro is used with its spin vector along the spin vector of the vehicle, the steady-state response of the gyro is a nonlinear function of the roll rate of the vehicle.