The Integrated Solar Array and Reflectarray (ISARA) antenna requires a rugged circuit board material that will meet the following requirements: (1) remains sufficiently flat over the required operating temperature range with solar cells mounted, and under full solar illumination, including heat dissipation due to ≈30% efficiency solar cells; (2) provides a sufficiently high-quality RF-grade circuit board material needed to print the reflectarray antenna; (3) is sufficiently thin (<2.5 mm) to fit within the available stowage volume; and (4) has low mass density (≈5 kg/m2).
The initial plan for ISARA was to use a standard circuit board material such as Rogers 4003. However, structural and thermal analysis under orbital solar illumination showed that the surface of the circuit board bowed so severely that it prevented the use of the panels as an antenna. It was found that the thermal gradient through the ISARA panel (from one face of the panel to the opposite face) causes a severe bow in the panel. There was no available material that met the above requirements. This created a critical need to develop a new circuit board material.
Two candidate circuit board materials were developed that met the requirements. These materials were developed through an iterative process that utilized a detailed finite element method structural analysis to evaluate flatness performance with thermally induced stress (using a thermal model of a spacecraft in low Earth orbit and another thermal analysis based on a Mars flyby). The iterative design process led to the selection of specific materials and layer thicknesses that resulted in two different multilayer sandwich structures that met all requirements.
The circuit boards consist of a multilayer composite in which graphite composite structural core material, such as Tencate BTCy-1A, is sandwiched between layers of standard circuit board material such as Rogers 3003, 4003, 6002, etc. The central structural core is a multilayer composite structure layed up in a quasi-isotropic stack. The sandwich structure is co-cured together to avoid the additional thickness and process steps that would be required by bonding.
Two successful styles of this material have been developed: (1) Rogers 3003/BTCy-1A M55J composite/Rogers 3003 sandwich structure, and (2) Rogers 4003/BTCy-1A M55J composite/Rogers 4003 sandwich structure. A layup was designed that utilized Rogers 4003/T-300 woven composite/Rogers 4003 sandwich structure, but it proved to bow when fabricated. It is likely this bow was due to the woven fabric.
These boards are an essential element needed for the thin, foldable reflectarray antennas that JPL is actively developing for CubeSat applications. The antennas require a high-quality RF circuit board material (typical dielectric constant values in the range of 2–5 and loss tangent less than ≈0.003). However, these circuit boards do not have sufficient structural rigidity to function as a thin deployable antenna panel. Without the multilayer composite material developed in this work, the folded panel reflectarray antennas could not have been developed.
This work was done by Richard E. Hodges, Long Y. Chen, and Armen S. Toorian of Caltech; and Eric Oakes of Space Exploration Technologies Corp. for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Technology Transfer at JPL
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Refer to NPO-49539.