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.     

Enhanced Power Generation of GSS4PS by Optical Solar Reflectors

A novel arrangement is proposed to enhance the power generation capabilities of a gravitationally stabilized solid-state-satellite solar-power station (GSS4PS) spherical solar collector. The unilluminated portion of a GSS4PS is illuminated by employing optical solar reflectors. The different mechanisms required for implementation of this arrangement are already space proven. The detailed study of this arrangement made by the authors reveals that practical realization of this concept will enhance the power generation capability of the GSS4PS and simultaneously reduce the weight per unit power and cost per unit power in GSS4PS spherical solar collectors.     

Inertially fixed pitch stabilization of satellites by solar radiation pressure

Utilization of solar radiation pressure to stabilize the pitch attitude of an unsymmetrical satellite along an inertially-fixed orientation is investigated. A controller employing two rotatable highly reflective control surfaces is proposed and a control strategy involving both nominal and feedback controls is synthesized. Accounting for the apparent annual motion of the Sun, the validity of the concept throughout the year is established through a stability analysis of the system. The influence of the Earth's shadow on the controller performance is also analyzed. The speed of response as well as the pointing accuracy capabilities of the system appear to be quite acceptable for long-life scientific missions.     

The German space processing programme TEXUS with sounding rockets

This paper reports on the objectives of the German space processing programme with sounding rockets and the scientific results obtained thus far.     

Dynamics of solar cosmic ray events: Processes at large heliocentric distances (⪢1 AU)

Observations of solar cosmic ray events far from the sun (?1 AU) became possible after the launch of Pioneer 10 in 1972. Four spacecraft have now travelled beyond the orbit of Jupiter - Pioneer 10/11 and Voyager 1/2 — and are producing a growing body of distant observations of solar cosmic ray events. Initial studies using Pioneer 10/11 data out to ～6 AU interpreted flare particle observations in terms of a diffusion model, including the effects of convection and adiabatic energy loss. This model enjoyed general success in explaining the time-intensity profiles in cases where the spacecraft connection longitude at the sun did not change significantly with time. The results implied that the radial diffusion coefficient (K_r) increased slowly with distance over that radial range. More recent results at larger distances imply that K_r may begin to decrease beyond ～5 AU. It is not yet clear whether the standard diffusion model will be adequate to explain solar events well beyond 5 AU. The fact that large events at very large distances can last up to two solar rotations implies that solar wind stream structure will also play a role in the event dynamics. In general, however, observations at large distances offer perhaps the best hope of separating interplanetary propagation effects from coronal storage and propagation effects which frequently dominate observed event profiles at 1 AU.     

Fragmentation in rotating isothermal protostellar clouds

Summary From the extensive set of numerical calculations briefly described above, it seems apparent that rotating, isothermal gas clouds are unstable to fragmentation under a wide range of conditions. (Caution: This result for isothermal clouds cannot be generalized to all clouds, as is shown, for example, by Boss's analysis [these proceedings] of the stability of collapsing, adiabatic clouds.) It is of importance to note, however, that no fragmentation is apparent during a cloud's initial dynamic collapse toward a disk structure; rather it is the rotationally flattened disk/ring configuration that undergoes fragmentation. This is a considerably different picture of fragmentation than has been presented, for example, by Hoyle (1953).The degree of instability and the mode (ring vs. blob) of fragmentation is sensitive to , but insensitive to . The initial amplitude of a perturbation does not appear to be crucial--fragmentation should occur eventually even for low amplitude initial NAPs.Finally, it is of some interest to know what the properties are of the fragments that break out of these isothermal clouds. Before outlining these properties we emphasize that in this set of calculations we have specifically excited the m = 2 (binary) non-axisymmetric mode; hence we have in some sense suppressed the development of other modes and we have promoted the development of equal mass components in the binary systems. In these evolutions, a typical fragment contained 15% of the initial cloud mass; had a specific angular momentum 25–30% that of the original cloud; had a ratio of spin angular momentum to orbital angular momentum 0.2; and itself had a ratio of thermal to gravitational energy _frag < 0.1. The formation of a binary system has therefore resulted in a conversion of some of the original cloud's spin angular momentum into orbital angular momentum, and has produced protostars with reduced specific angular momenta. It is also evident that each fragment is unstable to further collapse (having low ) under the isothermal assumptions imposed here.     

High-Speed Homopolar Inductor Alternators of Minimum Leakage Reactance

The leakage reactance of the machine is expressed as an equation involving slot leakage, end-connection leakage, differential leakage, stator-halves leakage, and tooth-top leakage reactance. This leakage reactance equation, or objective function, is then minimized under suitable constraints. Geometric programming is used to carry through the optimization procedure. A computer program is developed and applied to find the optimum leakage reactance for a 95 kVA, 208 V, wye-connected, 40 800 r/min aerospace alternator, using 8-, 10-, and 12-pole machines.