Gemini 1 Spacecraft

Its two-person capacity and greater capabilities meant that Gemini would be a substantially heavier spacecraft than Mercury had been — too heavy to be lofted into orbit by Mercury’s Atlas rocket. A replacement was needed. The newly developed Titan II ICBM (which had also been tapped by the Air Force for its X-20 spaceplane project) was an attractive replacement. It had a thrust some two and a half times that of the Atlas, a far simpler mechanical construction, and the ability to store propellants indefinitely. Moreover, the Titan II’s propellants mixed less violently than those of Atlas meaning a booster explosion, should it happen, would be less violent. This made obsolete the heavy escape tower used in the Mercury program; instead, ejection seats could be used. :41–42