"The world's most expensive science project -- the $100 billion-plus International Space Station -- is poised to get four more years in orbit. According to documents obtained by the Orlando Sentinel, NASA plans to announce this week that it has White House approval to extend the station's operations by four years until 2024. The decision follows years of pressure by top NASA officials, who consider the station a critical steppingstone to future exploration. But a four-year extension likely would cost NASA about $3 billion a year from 2021 to 2024. That's a major chunk of the agency's annual budget, which is now about $17 billion, and a longer mission could force NASA to make tough financial decisions in the future."
NASA Will Face Solomon's Choice in 2014, earlier post
"If a budget in the range of $16.6 billion is what happens NASA will have a major problem maintaining both the International Space Station (ISS) and the SLS/Orion Exploration program. Given that the funds are simply not going to be available to keep the ISS alive and functioning and to fully construct and operate the SLS/Orion system, something has to give. Are we going to have to kill one to insure the other's survival? That is the choice that that is presenting itself - a clear recipe for disaster as far as NASA's human space flight plans are concerned."
"First, it will allow NASA to complete necessary research activities aboard the ISS in support of planned long-duration human missions beyond low-Earth orbit--including our planned human mission to an asteroid by 2025 and to Mars in the 2030s. NASA has determined that research on ISS is necessary to mitigate fully 21 of the 32 human-health risks anticipated on long-duration missions. A related critical function of ISS is testing the technologies and spacecraft systems necessary for humans to safely and productively operate in deep space. Extending ISS until 2024 will give us the necessary time to bring these systems to maturity."