The prime mission of a project is activities in the period of operation proposed by NASA when it was selected for funding. The United States Congress passes a budget detailing where Federal tax money is to be spent in the upcoming year. The budget includes funding for NASA, sometimes with explicit instructions on how to allocate money to the project level, based on NASA's recommendations. The duration of a project may vastly exceed the prime mission, and money spent on a project during its lifetime may vastly exceed the original budget.