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Tham khảo tài liệu 'aerospace technologies advancements 2012 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 168 Aerospace Technologies Advancements Fig. 2. Thermal analysis for powered electronic boards in the satellite 3.4 Vacuum Vacuum is not a problem for sealed electronic components but reduces the power dissipation capability due to missing convection leaving only conduction and radiation to the outside. This problem is related to the temperature ranges outlined above. The board that dissipates more heat is the one responsible of data transmission as it hosts the power amplifiers we successfully tested it in a thermal vacuum chamber with a temperature range of -20 50 C and a pressure of 10Pa. While the expected pressure at the orbit altitude is some order of magnitude lower we considered the level that we could achieve with inhouse equipment sufficient to assess the board reliability. Other boards were simulated using their nominal characteristics taking into account de-rating because of the absence of convection. 3.5 Vibrations Forces and vibrations applied to the satellite during the launch are very high and might cause physical damages as well as disconnection of electronic devices and disengage of electrical connectors. A careful choice of packages i.e. no BGA devices more sensitive to vibrations mounting technologies and overall structure is therefore mandatory. PCBs see Figure 3 for an example have small size about 12 X 8 cm2 and are mechanically blocked at the four edges therefore vibrations are kept within acceptable limits. More bulky components are secured to PCB but connectors represent a critical point. Direct board-to-board connectors are kept in place by the mechanical fixture of boards. Other connections use flexible PCBs or small flat cables in these cases silicon glue is used to keep in place the movable part. Specifications and requirements with respect to static loads and vibrations were established by the launcher company Kosmotras and Yuzhnoye Design Office http www.yuzhnoye.com and verified by simulations and ground tests. Mechanical tests for