What is the highest number of people occupying the ISS at on time ?
NASA originally planned in the 1980s to develop " Freedom " alone , but US budget constraints led to the merger of these projects into a single multi-national program in 1993 , managed by NASA , the Russian Federal Space Agency ( RKA ) , the Japan Aerospace Exploration Agency ( JAXA ) , the European Space Agency ( ESA ) , and the Canadian Space Agency ( CSA ) .