Trade studies on IR gimbaled optics cooling technologies

As advanced space based IR target acquisition and tracking systems continue to mature, the necessity to remove heat across a two-axis gimbal joint has become a critical requirement. Heat loads and duty cycles continue to increase, making current solutions no longer tenable. The thermal bus focused technology area, a member of Air Force Research Laboratories (AFRL) under the Space Vehicles Directorate, conducted a system level trade study of the different methods and technologies under consideration. The two axis gimbal joint problem can be solved in one of two major ways from a heat transport perspective. Either the cryocoolers that cool the sensors can be kept on the gimbal near the optics, known as the ambient solution, or they may be remotely located on the main body of the spacecraft, known as the cryogenic solution. If they are kept on the gimbal, the primary concern becomes the ambient heat rejection from the compressors while removing the cryocooler system requires efficient transport of cryogenic cooling. Several standard and advanced heat transport technologies including rotatable joints, flexible heat pipes, thermal straps, mechanically pumped fluid loops (PFL), capillary pumped loops (CPL), and loop heat pipes (LHP) exist that are capable of solving this problem from either the cryogenic or ambient transport viewpoint. Thermal straps and rotatable joints were not considered after first order designs showed these options to be unfeasible due to complexity or inefficiency. Cryogenic and ambient CPLs, LHPs, PFLs and flexible cryocoolers were compared with a top level analysis using an iterative scheme to calculate system parameters such as temperatures, thermal loads, masses, and power consumption.