August 22, 2015 – Taiwan began to collaborate with US company on designing and developing its own satellite since 1994. In January of 1999, the first satellite FORMOSAT-1 was launched, and retired in 2004. Later in 2004 and 2006 FORMOSAT-2 and FORMOSAT-3 were also launched. In 2010, FORMOSAT-5 passed all design verification, and is waiting to be deployed. FORMOSAT-5 will carry the payload of Optical Remote Sensing Instrument completely designed and developed by Taiwan itself the first time.
Currently the FORMOSAT-8 satellite is already under development. FORMOSAT-8 will inherent the experience from FORMOSAT-5, and also carry the Optical Remote Sensing Instrument developed by Taiwan. The Opto-Mechanical system integration will be leaded by the Instrument Technology Research Center, and participated by the Opto-Mechanical Design Analysis (OMDA) Lab supervised by Professor Yi-Cheng Chen at the National Central University, who will be responsible for weight reduction of the mirror supporting structure. In order to tackle this challenge, the OMDA Lab utilizes SmartDO to achieve breaking through improvement.
Optical Remote Sensing Instrument Payload
The remote sensing instrument (RSI) which is used to take images for ground surface observation, will be exposed to harsh environment including vacuum, large temperature difference, high launch acceleration and random vibration. Therefore both the optical quality and the strength of mechanical structure should be considered when designing the optical system of a RSI. Figure 1 and Figure 2 shows the appearance of the optical remote sensing instrument payload on FORMOSAT-5 satellite.
Building Up Design Optimization Model and Process
In order to maintain good performance and low weight simultaneously, it is necessary to optimize the structure of the mirror. To accomplish this challenging task, the development team utilizes SmartDO as the tools and platform for design optimization. Upon the SmartDO platform, the team links together CAD and finite element software to optimize the characteristic dimension of the mirror structure. The goal is to obtain light weight, high stiffness and high-quality optical performance.
Figure 3 shows the design optimization process that has been built on SmartDO, which includes seamless integration among SOLIDWORKS, ANSYS and SmartDO. Under this architecture, the user defines design limitation and requirement like allowable stress and dimension bounds, and SmartDO will drive CAD and CAE automatically to perform design optimization. With the direct global search technology of SmartDO, design sensitivity study is not necessary, so the team can devote more resources on other tasks to achieve even better results.
Analysis and Design Optimization of the Mirror Structure
The mirror structure in FORMOSAT-8 follows the design in the PLEIADES–KORSCH TELESCOPE space project by by THALES SESO. The main supporting structure has a hexagonal frame with honeycomb substructure within. (Figure 4). Buttress structure from the SOFIA satellite made by REOSC is also used to reduce the deformation on the edge of the mirror structure due to cantilever effect (Figure 5). Twelve (12) design variables for the geometric parameters were defined. Figure 6 shows the geometry of the initial design.
The twelve design variables includes the characteristic dimension of the main structure, the buttress structure and the honeycomb substructure. The structure needs to sustain the gravity and the polishing pressure. The deformation in specific directions and locations should be under allowable value for different loading conditions. The design optimization formulation is defined as
SmartDO Significantly Reduces the Weight of the RSI Payload
After the model is defined by the user, SmartDO can solve the problem in a fire-and-forget manner without tedious sampling and sensitivity study. Finally, SmartDO successfully reduce the weight from 9.8 kg to 8.8 kg. With the verification by finite element analysis, all the performance indices were proven to be at least equal to the original design. This has been a important break through for the development of FORMOSAT-8 satellite. With the powerful tool like SmartDO, the team was able to verify the feasibility of weight reduction, and carry on this experience for further advanced study.
Chia-Yen Chan, Bo-Kai Huang, Zhen-Ting You, Yi-Cheng Chen, Ting-Ming Huang, “Optimal Lightweight Design of a Primary Mirror on a Remote Sensing Instrument”，CSMMT2014, November 2014, Taichung, Taiwan.
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