NASA named the program GEMINI after the twin stars Castor and Pollox, one of the 12 constellations of the Zodiac.

The Gemini missions had the following challenges to meet prior to attempting lunar missions:

• Rendezvous and docking
• Long duration flights
• Multiple-hour work outside the spacecraft
• Advanced, reliable on-board flight systems
• Training of flight and ground crews.

It was during the Gemini Program that the United States caught up with and surpassed the Soviet Union in the race to the Moon.