One might think that fusion propulsion requires some exotic fuel to propel a rocket a million-or-so-times more energetically than standard chemical fuels.
有人可能会认为聚变推进需要一些能量高于标准的化学燃料一百多万倍的稀有燃料推进一个火箭。
3
The Earth holds other, less-accessible fuels, such as tar sands, and a more exotic possibility in the form of icy methane hydrates.