Gemini
USA Wikipedia 
Built & Operated By
National Aeronautics and Space Administration
Government · founded 1958
Maiden Flight
8 APR 1964
Flight Life
Between a few hours and multiple days (14 day is the maximum achieved).
About
The spacecraft was 18 feet 5 inches (5.61 m) long and 10 feet (3.0 m) wide, with a launch weight varying from 7,100 to 8,350 pounds (3,220 to 3,790 kg).
Spacecraft Specifications
Height
5.61 m
Diameter
3 m
Crew Capacity
2
Rating
Human-rated
Capability
Human transportation to low Earth orbit.
Operational History
The Gemini crew capsule (referred to as the Reentry Module) was essentially an enlarged version of the Mercury capsule. Unlike Mercury, the retrorockets, electrical power, propulsion systems, oxygen, and water were located in a detachable Adapter Module behind the Reentry Module. A major design improvement in Gemini was to locate all internal spacecraft systems in modular components, which could be independently tested and replaced when necessary, without removing or disturbing other already tested components.