The UN (Interstellar) Space Exploration Corps was the space agency of the United Nations.
It was formed as UNSEC to unlock the wealth of the Sol system. In 2042 they moved an asteroid into Earth's orbit to provide supply of metal. The profits went to the Line One industries that had paid for the venture.
With the discovery of the Tal-Seto stardrive in 2055, the UNSEC was renamed to UNISEC. It soon discovered two planets tha would support life and undertook an ambitious colonization program with their Colony Transport (CT) ships. First call went to Line One citizens but a groundswell of enthusiasm rose on the third world, who saw colonization as release from poverty and violence. Since the CTs were not big enough, riots and protests broke, threatening the stability of the half the world.
The UN responded by opening Mars for colonization, commencing construction of orbital habitats, a fleet of CTs, and vastly enlarging the Earth Transfer Station. Colonists crammed into shuttles to the ETS in a never-ending stream.