Right now, one key technological problem for solar-sail spacecraft lies in how to efficiently unroll solar sails in space.
目前，光帆飞船的一个关键性技术难题在于如何在太空中高效地展开太阳帆。
The design of the joints between cable and arch rib is a difficult, but key technological problem in the construction of tied arch bridge.
吊索与钢管拱连接节点的设计是系杆拱桥建设中的关键技术难题。
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