The technology for a steerable spacecraft radiator with a fully functional rotary joint capable of operating with anhydrous ammonia would be very beneficial for thermal control systems onboard future spacecraft. Different slipring rotary joints capable of continuous 360 deg rotation and a flexible pressure line joint or "twist capsule" with oscillatory motion were investigated. A rotary joint with commercial-off-the-shelf ethylene propylene diene monomer O rings and one with ethylene propylene diene monomer O rings that were preconditioned to be compatible with ammonia were designed and tested, and they were determined to not be viable candidates for a rotary seal with ammonia working fluid. A rotary joint with ultrahigh-molecular-weight polyethylene lip seals was also explored and has demonstrated at least an equivalent 15 year life in low Earth orbit. The ultrahigh-molecular-weight polyethylene lip seal rotary joint has a dynamic sealing capability from at least −15 to 70°C. A flightlike unit is being built with enhanced fidelity to be tested and qualified for flight. In parallel to the 360 deg rotary joints, a twist capsule rotary joint was also designed and tested. The twist capsule oscillates between 0 and 270 deg, and the first-generation model demonstrated a life capability equivalent to 27 years in low Earth orbit. An improved flightlike twist capsule rotary joint is in development to be tested and qualified for flight. Nomenclature Q L = leak rate of the rotary joint, standard cm 3 ∕s V = volume of rotary joint ΔP = pressure drop of rotary joint, bar Δt = change in time, s

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