Solid rocket motor design is a complicated systems engineering.

固体火箭发动机设计是一项复杂的系统工程。

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At the same time, the engineering department made shells of the solid models.

同时，工程部门制作实体模型的外壳。

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At the same time, the engineering department made shells of the solid models.

同时，工程部门制作实体模型的外壳。

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