Ball valves offer numerous benefits in thermal control system applications. Straightforward to design and consisting of few parts, ball valves can be more compact than other styles of valves, saving mass and volume. Reconfigurable for specific functions, a ball valve can provide proportional control and/or isolation. The valve seats allow robust sealing for internal leakage while maintaining a low actuation torque, allowing ball valves to be actuated in many ways, including the ability to turn by hand for manual override functionality without needing extra gearing or long lever arms. Ball valves also have a comparatively low-pressure loss, especially in the fully open position, which benefits the often-limited pressure loss budget of a spacecraft thermal control system. Ball valve components require less restrictive tolerances and are mostly axisymmetric making them readily manufacturable. Ball valves have proven quite durable, handling the loads during the launch and descent of spacecraft. The general methodology for designing ball valves is also consistent across a large range of sizes. In addition to all the performance benefits, the modularity of ball valves to perform different tasks can reduce nonrecurring engineering cost of a system. Due to this cost reduction and adequate performance characteristics, Sierra Space is developing a line of modular ball valves. These valves, evolving from previously qualified Sierra Space ball valves, can proportionally control, isolate, and divert flow. This paper will discuss the advantages of ball valves in spacecraft thermal control systems and detail the development of Sierra Space's line of modular ball valves.
Rorabeck et al. (Sun,) studied this question.