The Plutonium Problem: Who Pays For Space Fuel?
"When NASA's next Mars rover blasts off later this month, the car-sized robot will carry with it nearly eight 
pounds of a special kind of plutonium fuel that's in short supply."
"NASA has relied on that fuel, called plutonium-238, to power robotic missions for five decades."
"But with supplies running low, scientists who want the government to make more are finding that it sometimes seems easier to chart a course across the solar system than to navigate the budget process inside Washington, D.C."