Influence of curved thin-film device on deformation of a solar sail

A spinning solar sail IKAROS’s membrane is estimated to unexpectedly deform into an inverted pyramid shape due to thin-film devices with curvature, such as thin-film solar cells and steering devices on the membrane. It is important to investigate the deformation caused by the curved thin-film devices and predict the sail shape because the out-of-plane deformation greatly affects solar radiation pressure (SRP) and SRP torque. The purpose of this paper is to clarify the relationship between the global shape and orientation and position of curved thin-film devices and to evaluate SRP torque on the global shape using finite element analysis. The global shape is evaluated based on the out-of-plane displacement and the SRP torque. When the curved thin-film devices make the membrane shrink in the circumferential, diagonal, and radial direction, the sail deforms into a pyramid shape, an inverted pyramid one, and a saddle one, respectively. The saddle shape is more desirable for solar sails than the inverted pyramid shape and the pyramid one from the viewpoint of shape stability to SRP and control of SRP torque in the normal direction of the sail (windmill torque). The position of the thin-film device tends to increase the absolute value of windmill torque when it is biased circumferentially from the petal central axis. The suggested design principles for the arrangement of thin-film devices is that the curved thin-film devices should be directed so that the sail shrinks in the radial direction in order to deform the sail into a saddle shape with high shape stability, and the position of the thin-film devices should be biased in the circumferential direction paying attention to the absolute value of windmill torque to determine the direction of windmill torque.     

Solar power sail membrane prototype for OKEANOS mission

This paper reports on the manufacturing and evaluation of a solar power sail membrane prototype for the OKEANOS project. The in-house prototype was built by the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. Mechanical and electrical evaluation tests were conducted. The membrane, thin-film solar cells, reflectivity control devices were good condition after the manufacturing and handling. The improvements in the manufacturing process and design were found. The manufacturing process and design were fundamentally established. After the prototype, improvement plans for the manufacturing process and design were tried. We have a prospect of manufacturing the flight model sail and continue to the development.     

Efficient Utilization of Orbit/Frequency for Satellite Broadcasting

In this paper some basic concepts involved in efficient orbit/spectrum utilization for broadcast satellites are discussed. A theoretical analysis leads to the determination of interference zones and minimum number of frequency channels required for homogeneous systems operating in the 800-MHz and 12-GHz bands. A crossed-beam arrangement of satellite systems is proposed, in which the beams from satellites to service areas cross each other. This arrangement has a more efficient orbit spectrum utilization compared to the identical-longitude approach, in which the subsatellite point has the same longitude as the center of the service area, Based upon practical considerations, the elemental number of frequency channels required for world-wide coverage has been calculated in relation to satellite orbital position, for single-beam and multibeam satellite systems, using the identical-longitude and crossed -beam arrangements.     

Ionospheric and thermospheric responses during August 1972 storms — A review

Various reports of ionospheric responses during the August 1972 storm events are reviewed with respect to the phenomena in three major world sectors, N-S America, Afro-Europe, and Austro-Asia, in order to have a global picture. Emphasized highlights are (1) extensive investigation of the sudden increase of the total electron content estimated from Faraday-rotation measurements of satellite signals; (2) a dramatic upward surge above 300 km altitude, soon after a flare, measured by the Millstone Hill incoherent scatter radar; (3) electron density profiles, electric fields and conductivities, and neutral winds, at the time of the geomagnetic storm sudden commencement and during the succeeding storms, measured by the Chatanika incoherent scatter radar; and, (4) approximately 2.5-h oscillatory F2 density variations in Eastern Asia during the F2 storm main phase. To show temporal variations of the latitudinal distributions of storm-time F2 electron densities, in three longitudinal sectors separated about 60° longitude each, newly investigated results of the F2 hourly data at 35 stations in the Asia-Australia-Pacific sector are then exhibited. Finally, current theories or at least theoretical ideas of ionospheric storm mechanisms are briefly introduced, and a few remarks on the August events in the light of those theories are presented.