Reaearch On Key Techniques Of Thermal Control For Space Robotic Arm

The space robotic arm is key to the successful assembly of the Space Station, themaintenance of its external systems, astronaut Extravehicular activity support, andthe servicing of external science payloads. The entire service life of the arm is alongwith the beginning and ending of the station life. As the fine small arm of China’sspace station robotic arm system, the arm was designed with longevity andcomplicated attitude configurations. The inner heat loads are pretty much and theworking time is long, all these have raised new challenges to its thermal design. Withlarge power consumption, thermal conductance path of the highly integrated andmodular joint is very complicated. It needs more heating power to keep theopening-end effector warm under non-operating mode, because the heat leakage ofthe opening-end effector is badly and uneven. It’s hard to conduct the inner heatloads of hand-eye camera’s lighting component to outer space. It’s difficult todetermine the analysis cases and the ground-testing cycle is long. The main contentof this paper is how to use sophisticated thermal design technologies to solvethermal design problems of the space robotic arm so that the in-orbit temperature canmeet the requirements.The present research status of space manipulator throughout the world wassummarized in this paper. Also the working characteristics and thermal designfeatures of space manipulator were summarized. Besides, the thermal design scheme of component of typical abroad space robotic arm was described. On this basis, thestructures and mode of the fine small arm of China’s space station robotic armsystem were analyzed. The difficulties and the keys that the thermal design facedwere summarized.The Orbit of the space robotic arm is low Earth orbit. The main factors that causedthe degradation of thermal control materials under LEO environmental are atomicoxygen, particle radiation, thermal cycling and space debris. According to theservicing missions of Hubble Space Telescope(HST) and related flight testing ofCanadarm2, the atomic oxygen effect of Low Earth Orbit was introduced.Degradation of outer film of multi-layer insulation in LEO and design of long-livedfilm were described.A concrete thermal design for the joint, end-effector and hand-eye camera of thespace robotic arm was carried on. The hot case and cold case conditions weredetermined according to the in-orbit attitude and working feature of the arm. Typicalconditions were analyzed and calculated to determine the size of each radiatingsurface and the consumption power of supplementary heating. The results show thatthe joint temperature is-22℃~+23℃and the end-effector temperature is-22℃~+30℃and the hand-eye camera temperature is-5℃~+31℃in cold caseconditions. It meets the design requirements of storage temperature.The temperature of the internal components of joint is very high in hot caseconditions, because the inner power consumption of the joint is pretty much and it’sdifficult to conduct the heat to outer space. Sensitivity analysis of thermal designparameter for main parameters that affect the heat radiation were developed. Theresults show that the heat source was the main parameter that affect its internaltemperature, and the range of sensitivity variety was2℃~5℃. The temperature ofthe joint that after optimized design meets the design requirements because theposibility of the worst case was less.The rationality of thermal control indicators were proved by the thermal vacuumtest of single joint and end effector. With large volume and complex structure, the period of the test was long and the expensive of the test was extrotionate. In order topredict the balance temperature of thermal balance test for the space arm, theiterative equation that base on node network method for predicting the thermalbalance temperature was established. Based on a large number of experimental data,a statistical analysis for three factors that influenced the results of the iterationequation was done. And a reasonable range of each factor was determined ultimately.