WHITFIELD: All right, for decades, the U.S. and Russia have put aside their differences to cooperate in space. Now the crisis in the Ukraine and rising tensions between the two nations could cause big problems for the U.S. space program. Here is CNN's Jim Sciutto.</s>JIM SCIUTTO, CNN CHIEF NATIONAL SECURITY CORRESPONDENT: They were all smiles in the International Space Station this week, but could this be one of the last times American astronauts and Russian cosmonauts journey together through space? Russian officials are taking the battle over Ukraine into orbit, vowing to abandon the space station four years early in 2020. And banning Russian made rocket engines to launch U.S. military satellites. The deputy prime minister even suggested astronauts instead use a trampoline. And this is no small problem because since NASA retired the shuttle in 2011, American astronauts have no other way up or down than hitching rides on Russian rockets.</s>JIM LEWIS, CENTER FOR STRATEGIC AND INTERNATIONAL STUDIES: The Russian announcement means we need to rethink our reliance on them because it shows we are dependent on them in ways that might have made sense 10 years ago, but doesn't make sense anymore.
Russian U.S. Space Partnership At Risk