Development of a Rotary Joint for a Steerable Spacecraft Radiator

Abstract

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 slip-ring 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 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.