So far NASA is exploring two options for propulsion there? A nuclear thermal rocket and a chemical engine.
迄今为止NASA研究了两种前往那里的备选推进器：核热火箭和化学发动机。
The rocket uses a nuclear engine, a technology that was under serious investigation for a long time (and may yet see its day in space).
宇航员的火箭使用的是核动力引擎，该技术长久以来都处在认真研究之中（但至今仍未能投入实用）。
The rocket USES a nuclear engine, a technology that was under serious investigation for a long time.
火箭采用的则是人们长期以来一直认真研究的核动力引擎技术。
The rocket USES a nuclear engine, a technology that was under serious investigation for a long time.
火箭采用的则是人们长期以来一直认真研究的核动力引擎技术。
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