United Earth Space Probe Agency
The United Earth Space Probe Agency (UESPA) began almost immediately following First Contact with the Vulcans in 2063. It was a conglomeration of many existing and recently formed space agencies around Earth whose goal it was to collectively begin the exploration of space in earnest. It's first major success was a series of probe launches beginning in 2065, culmulating with the Friendship series that were sent toward the Delta Quadrant two years later.
UESPA was the premier space-exploration agency on Earth until the 2130s. By then, Starfleet had surpassed it in importance, although the two would work together on many projects and missions well into the 24th Century. This included the sharing of engineers and scientists to build spacefaring craft, such as the NX-Class project in 2150 and the Excelsior class in the 2280s-90s. While Starfleet focused on manned ships for exploration, the UESPA continued to develop and launch umanned probes and satellites.
Both UESPA and Starfleet personnel oversaw the initial conference to develop a possible Coalition of Planets in 2155.
While Starfleet ranks were based on Terran naval traditions, the UESPA maintained ranks of army and/or Marine origins.