STS-135 T-24 days - Gemini Flights Prove Orbital Mechanics are Hard

The Gemini program consisted of ten manned flights in two and a half years.  Sending men into space was becoming pretty standard.  At the time, I didn't realize how Gemini was testing all the capabilities needed to get to the moon.  I just thought they were doing lots of cool things.  The first flight, Gemini III, was the first time two Americans flew in a spacecraft. On Gemini IV, Astronaut Ed White made the first US spacewalk.  And, the cool stuff kept happening.

Ed White performing the first American EVA

But it wasn't all about doing cool things.  On Gemini III, they also used thrusters to change the orbit of the spacecraft.   Gemini IV used the thrusters to try to rendezvous with the booster rocket that had launched them.  But orbital mechanics held some surprises.  When they used the retro rocket to try to slow down, it actually caused them to drop closer to Earth.  Being closer to Earth, the Gemini capsule sped up because of the gravitational forces.  If you have ever played one of those toys where you drop a marble or coin into a cone like platter, it rolls slowly around and moves to the center and as it gets to the center it goes faster and faster...  That was the experience.  Slow it down and it goes lower then speeds up.  Orbital mechanics was interesting.  We would need more practice

During Gemini, there were lots of problems.  None of them resulted in casualties, but there were tense moments.  Gemini IV's space walk, called an Extra Vehicular Activity (EVA), tested the spacesuit flexibility to prepare for the walk on the moon.  When they went to open the hatch, it wouldn't open,  The astronauts worked on it for a while and finally got it open.  During the EVA, the question looming was, will they be able to get the hatch to close so they can return to earth.  They did.

Gemini 8 about to dock with the Agena

 Gemini V was the first to use a fuel cell. Yes, like people are trying to use for electric cars.  They were developed for the space program to generate power and water for the long trip to the moon and back.  It enabled them to stay in orbit for 8 days, the time needed to get to the moon and back!

Rendezvousing was hard.  We needed practice.  When Gemini 8 finally was able to rendezvous with a test docking vehicle. the two spacecraft went out of control and started rolling.  Later they determined it was due a stuck thruster on the Gemini.  Neil Armstrong barely got the two undocked and quickly did and emergency reentry to save the spacecraft.  Ugh, close call.  We need even more practice.

http://en.wikipedia.org/wiki/Gemini_4