Following the successful mating of its modules, Gemini spacecraft No. 2 began the second phase of Spacecraft Systems Tests (SST) at McDonnell. SST continued through September. During August and September, test operations alternated with the receipt and installation of a number of flight items in the spacecraft.

Vibration testing of the spacecraft and systems was successfully conducted August 20-24. No altitude chamber tests were performed on spacecraft No. 2 because the Gemini-Titan 2 mission was to be unmanned. Phase II mated SST concluded with the Simulated Flight Test September 3-15. The spacecraft acceptance review was held September 17-18, after which it was flown to Cape Kennedy September 21.