The layer of sky above the cruising height of commercial aircraft and below satellite orbits was, until recently, regarded by most people to be empty space.That changed after a gigantic Chinese balloon drifted across North America 20km above the ground, followed by three more mysterious objects with lower altitude flight paths, which were all shot down.
以往大部分人都以為，在商業飛機巡航高度以上、衛星軌道以下的這段天空就是空無一物的空間。
您已閱讀5%（398字），剩余95%（7927字）包含更多重要信息，訂閱以繼續探索完整內容，并享受更多專屬服務。