Gemini V
The Gemini V mission was mostly about endurance and overcoming problems that might be associated with an extended period of time in space. During this extended mission time, a number of scientific experiments were planned to occupy the astronauts time, but it did not include any space walks.

NASA PHOTO: Gemini V crew members Charles "Pete" Conrad, Jr. (left) and Gordon Cooper, Jr. Conrad had a reputation for joking and referred to the mission as "Eight days in a garbage can."
Gemini V mission was to be 8 days, the amount of time it would take to get to the moon and back. To accomplish this a new innovation would be deployed that would make this possible: fuel cells. Previous missions had used batteries that had limited life spans. The new fuel cell could be used for much longer period of time. A fuel cell converts chemical energy from a fuel into electric energy.
One of the experiments was to rendezvous with a pod that would be deployed from the capsule. However, problems with the fuel cell severely curtailed most of the scheduled experiments.
Just a few hours into the mission, the crew ejected the pod, but while they were out of radio contact, they noticed pressure drop in one of the fuel cells and Conrad decided to power down the fuel cells, meaning they were operating on backup batteries. If the problem couldn't be corrected, the mission would have to be aborted.

NASA PHOTO: View from Gemini V of Florida coastline and Cape Canaveral.
After some discussion it was decided to turn the fuel cells back on and run a series of tests to determine their viability. After this testing it was decided that the cells could remain on, but many of the scheduled experiments would have to be scrapped including the rendezvous with the deployed pod. A makeshift virtual rendezvous plan was devised and they successfully accomplished these tasks. But other than that, most of the mission was spent drifting in space, without heat, and it became a mission of endurance to overcome the cold and boredom.

NASA PHOTO: Astronaut Charles Conrad Jr. inside the Gemini 5 spacecraft as it orbited the Earth. Astronaut L. Gordon Cooper Jr. took this photograph. Although this photo shows Conrad suited up with helmet on, this was only done during liftoff, reentry or when performing other maneuvers while orbiting such as docking or space walks.
On the fifth day a problem developed when one of the thrusters stopped working. It was decided the mission could continue, but no experiments requiring the thrusters could be performed. This left just photographic experiments and medical tests.
With splashdown on August 29, 1965 the United States laid claim to the title of the longest space flight at 190 hours and 55 minutes. A safe landing and healthy crew after an eight-day voyage increased NASA's confidence in achieving its lunar-landing goal during the decade of the sixties.

NASA PHOTO: Astronauts L. Gordon Cooper Jr. (left) and Charles Conrad Jr. are seen in the Gemini 5 spacecraft in white room at Pad 19 just after insertion.