"The [Earth sciences] decadal survey, however, which lists 15 high-priority Earth science missions, also calls for adding $500 million or more annually to NASA’s $1.4 billion Earth science budget. Freilich [director of NASA’s Earth Science Division] and others have estimated previously that doing all 15 missions by 2020 would require spending as much as $4 billion during peak development years. Under the five-year plan Obama sent Congress last February, NASA’s Earth science budget would grow to only $1.65 billion by 2014. 'Frankly, we’ve got to come up with an executable program for the future,” Freilich said. “The decadal survey objectives were great, but they require a much larger budget. There is no point hitting our heads against a wall and trying to do more than we can do well.' "
The Earth sciences Decadal Survey proposed an excellent set of missions, but the priorities apparently assumed a budget that wasn't possible. (Although there are reports that NASA's budget will receive $1B more per year to be split between manned exploration and Earth sciences.)
Editorial Thoughts: Fixed or even shrinking budgets are a real risk to any 10 year plan. I hope that the planetary Decadal Survey recommendations will be structured to remain meaningful even if budgets shrink or missions in development go over budget.
SpaceNews Article: http://www.spacenews.com/civil/091231-nasa-budget-earth-science-lags-behind.html
Earth Sciences Decadal Survey: http://nasascience.nasa.gov/earth-science/decadal-surveys