Once positioned in space, the Hubble Space Telescope will capture light from sources (that are ) twenty times fainter compared to those that can be detected by ground-based instruments
这样把省略补出来就清楚了,句子的主干是the Hubble Space Telescope will capture light from sources,之后的都是隶属于(that are ) 定语从句之内的成分
Once positioned in space, the Hubble Space Telescope will capture light from sources (that are ) twenty times fainter compared to those that can be detected by ground-based instruments
这样把省略补出来就清楚了,句子的主干是the Hubble Space Telescope will capture light from sources,之后的都是隶属于(that are ) 定语从句之内的成分