CO2 Observer Failure (Taurus XL issue - fairing)
Sounds like the fairing on the Taurus launch vehicle failed to separate, sounds like a total loss of mission ($270 mil).
Too bad, the fact that we haven't been able to balance the CO2 books -- unknown sinks -- is a real source of uncertainty in climate change modelling. Had this mission made progress in nailing down global CO2 sources and sinks that would have been a big help, with possible explanations that might have either boosted either side of the debate.
http://news.bbc.co.uk/2/hi/science/nature/7907570.stm