Later this month, NASA will be launching the Orbiting Carbon Observatory (OCO): the first satellite designed to make precise measurements of carbon dioxide release and absorption around the world. This should provide important new information about how carbon dioxide is being emitted from human activities and degraded sources (such as decaying forests), as well as the operation of those natural sinks that continue to absorb atmospheric carbon dioxide.
The OCO will work using three parallel high-resolution spectrometers, being fed light by a common telescope. They will simultaneously measure concentrations of CO2 and molecular oxygen.
The new satellite will be placed at the front of a string of satellites in the same orbit: the Earth Observing System Afternoon Constellation, known more informally as the A-train. By having the satellites all look at the same areas in quick succession, the data from their various instruments can be assembled into a single high-quality, three-dimensional dataset. Five satellites are already in orbit, with two planned, including the OCO.
If all goes well, the OCO should be in orbit on February 24th.
[Update: 24 February 2009] It seems the launch has failed and the satellite has been destroyed. This is very disappointing: a blow to climate science, and to our chances of avoiding dangerous climate change. Hopefully, NASA will rebuild the satellite and try launching it again.
That would be a much better expenditure of resources than adding to the ISS or flying shuttles.