Reference

The Gemini 7 mission encountered several significant challenges:

1. Extended Duration: Gemini 7 was a 14-day mission, aimed at testing the effects of long-duration spaceflight on astronauts. This was one of the longest missions of its time, posing both physical and psychological challenges for the astronauts.

2. Weightlessness: The mission allowed scientists to study the physical toll of extended periods of weightlessness on the body. Maintaining health and efficiency over such an extended period required carefully monitored exercise routines and diet.

3. Spacecraft Constraints: The confined space of the Gemini spacecraft presented comfort and operational difficulties over the two-week mission.

4. Rendezvous Operations: Gemini 7 included the first space rendezvous with the Gemini 6A mission. The complexities involved in planning and executing the rendezvous tests were significant technical and logistical challenges.

5. Life Support Systems: Ensuring the reliability of life support systems over 14 days was a critical challenge. The systems had to work flawlessly to maintain air quality, waste management, and temperature control.

For more detailed insights, you can check out The first space rendezvous — Gemini 7/6A and NASA's overview of Gemini VII.