ULTRA-LIGHT CONCENTRATORS FOR SOLAR THERMAL PROPULSION

This paper presents ultra-light electromagnetic wave concentrators (EMCs) developed in the National Aerospace Laboratory of Japan (NAL), especially the electromagnetic wave concentrator with variable focal length (EMC/VFL), and their representative applications to a solar ray concentrator for solar thermal propulsion (STP) and solar power station (SPS). The EMCs with 220 mm, 430 mm, and 640 mm in diameters were made of ultra -light aluminized or silvered polymer membrane. The EMC/VFL consists of a pair of rectangular reflectors of ultra -light thin materials such as reflective polymer membrane, each of which has a line focus due to appropriate bending moment and axial force. The variable bending moment and axial force make the reflector a highly precise paraboloidal concentrator with variable focal length, and its characteristics as a concentrator are calculated. The two focus lines intersect each other perpendicularly so that a point focus can be formed at the intersection. Unlike a conventional paraboloidal concentrator including an inflatable type, the EMC/VFL can be folded up very compactly, and oblong huge area for an electromagnet ic wave receiver will be available in space. Because of their ultra-light weight and/or variable focal length, they can be more advantageous than the conventional or the inflatable type concentrator. In particular, the EMC/VFL is v ery promising when the concentrator area is quite large as for SPS, or over 10m 2 as for STP.