Science fiction series

[marwel7]

I have a memory of an episode in a science fiction series,but I can't remember which series it was.The story concerned the method of space flight in current use.A brother and sister,scientsts,had discovered that it was causing damage to space and in particular to their planet and set out to prove their findings.I think in the end one of them sacrificed him/herself to make the point.
Does anyone know which series this was,and which episode?

[james412]

Star Trek: The Next Generation - "Force Of Nature"

http://www.startrek.com/startrek/view/series/T NG/episode/68628.html

[marwel7]

Terrific,thankyou.I'm rewatching TNG at the moment and should get to this episode fairly soon.