A recent Space News article elaborates on NASA’s motivation to launch the next Landsat satellite—the Landsat Data Continuity Mission—by December 2012. LDCM will be launched on an Atlas 5 rocket, but if the launch date slips into 2013 the Atlas 5 schedule will become very busy with intelligence satellite launches, making LDCM not likely to launch until June 2013. A summer 2013 launch means that LDCM will miss the 2013 Northern Hemisphere spring growing season and it makes the possibility of a Landsat data gap more likely given the advanced age of both Landsat 5 and 7. A Thermal Infrared Sensor (TIRS) was added to the LDCM payload after the initial development of the Operational Land Imager (OLI) sensor had begun. The late edition of TIRS to LDCM had made the TIRS development timeline very aggressive.
+ “NASA Racing To Launch Next Landsat Mission Before 2013,” Space News [external link]