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Description
Spacecraft thermal interface selection has traditionally been driven by an over conservatism that has ultimately built in excess cost, assembly time, and suboptimal performance into builds for the past few decades. Machining tolerances, waviness of panels, and large area interfaces that bow or warp when bolted all combine to create interfaces that can have substantial out of flatness and gaps when assembled. Driven by a need to make reliable contact in these interfaces, liquid thermal solutions such as liquid silicone rubber or thermal greases have found widespread adoption in many spacecraft thermal interfaces despite significant downsides of working with these materials, including low conductivity, excess installation times and difficult rework, the possibility of pump out or bolt torque loss, and the potential for contamination and debris generation. Dry interfaces such as gaskets and gap pads can address the concerns of the liquid solutions including easier install and rework along with good thermal performance. However, adoption of these materials in many applications is hindered by an uncertainty regarding the ability to make and maintain contact in interfaces that are not fully flat. Thicker dry gaskets can help with making contact over larger areas, but thick gaskets are also often beset with challenges related to compression set that can result in torque loss at the bolts, potted insert pull out, and loss of contact upon thermal cycling. This work will discuss the performance of a unique, very low compression set thermal gasket for spacecraft thermal interfaces based a composite platform of vertically aligned carbon nanotubes anchored to an aluminum substrate. Using this low compression set form factor as an example interface structure, we present a first principles model based on Euler-Bernoulli beam theory that can accurately predict contact area and thermal conductance in vacuum for plates with a range of inherent curvature, bolt spacing, and plate waviness. We show experimental validation of contact area and conductance predictions for the carbon nanotube based gaskets as well as the influence of thermal cycling on the ability of the dry gasket to maintain contact. Lastly we discuss a novel layering strategy that enables targeted contact area enhancement in regions that otherwise would not make contact with a dry gasket, significantly opening up the viable application space for these carbon nanotube based gaskets.
