Deployable Passive Radiator Development

Due to the use of high-power payload electronics, today's spacecraft of all classes require generally larger payload radiators as the spacecraft body can provide. The use of deployable radiator seems to be the next logical step to achieve the required enlargement of the radiative area. Large deployable radiators based on two-phase heat transportation systems are today available, but these systems are technically complex and therefore not suited for smaller spacecraft, especially in future spacecraft constellations. We started therefore the development of an innovative deployable passive radiator, incorporating a high thermal conductivity panel. In our design the heat conduction will be maximized by introducing layers of high conductive graphite foils, which exhibit an 8 times larger in-plane conductivity compared to aluminum alloys of the same thickness. Graphite foils have a maximum thickness of only about 40 micro-meter and need therefore to be stacked to obtain the necessary radiator panel thickness. To increase structural strength and to compensate the low CTE of graphite, we propose an innovative solution with the graphite stack covered by thin aluminum sheets on both sides, which have integrated hooks penetrating into the graphite plate, thus increasing mechanical strength as well as out-of-plane thermal conductivity. Depending of mechanical requirements, the panel can be further strengthened with a thin honeycomb sandwich. The graphite foils extend over the panel area to form a flexible section, which is necessary to follow the deployment movement of the radiator. The flexible part is again fixed on the spacecraft side with the mentioned hooked aluminum sheets to represent a heat exchanger for collecting waste heat of the spacecraft. The paper will present the performed verification campaign, which includes mechanical / thermal analysis and sample testing, as well as mechanical / thermal test at breadboard level.