Complex sentence: Helena protests, but relents when he reminds her they will be in range of Terra Nova for only three more days; the fate of the entire colonisation effort and the three hundred men and women on Alpha rests on the information Russell can provide.
Split into simpler sentences: Helena protests, but relents when he reminds her they will be in range of Terra Nova for only three more days. The fate of the entire colonisation effort and the three hundred men and women on Alpha rests on the information Russell can provide.