So, they generally run on highly radioactivepower sources, which are dangerous even during launch.
所以，飞船的飞行通常依赖于高强度的辐射能源，这种能源甚至在发射时也是有危险的。
2
Any missions hoping to go farther will need a means of acceleration that can get the spacecraft to the edge of explored space faster—before it has depleted its radioactivepower source.
故而，任何更深空的宇宙探索都需要寻找技术途径来加速航天器，以便在放射性能源耗尽之前到达星系边缘。
3
Some elements such as uranium, commonly used as fuel in nuclear power plants, are always radioactive; there is no nonradioactive form of them that naturally occurs in nature.