semimajor axis of beam cross-section

例句：

1. 1. The satellite'ssemimajor axis is 200kilometers.
   卫星的半长轴是200公里。
2. 2. The planet's semimajor axis is 1.5 timesthe radius of the sun.
   行星的半长轴是太阳半径的1.5倍。
3. 3. The moon's semimajoraxis is about 384,400 kilometers.
   月球的半长轴大约是384,400公里。