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The trickle of oxygen became a steady stream, joining in a chemical reaction with hydrogen to produce the electricity to run the craft's computer, radar, communications and environment-control systems. For reasons not yet fully understood, the pressure inside the oxygen tank increased as the volume of liquid oxygen decreased while it was being used. Soon the fuel cell was supplying Gemini with all the electricity it needed, and the astronauts began switching their systems back on. Fuel-cell experts had actually underestimated the system's efficiency, were surprised that they could get sufficient power with such low pressure and so little oxygen fueling the cells. Had they known this beforehand, they could have permitted Gemini to spend enough power for the planned rendezvous with the Radar Evaluation Pod (REP) that it had previously ejected. By the time they found out, REP's batteries were dead, and it was too late.
On the third day up, the astronauts did the next best thing: they played a game of electronic tag. In an imaginary chase across the heavens, Cooper, in four precise maneuvers, closed the gap between the orbit of Gemini 5 and the simulated orbit of a phantom Agena rocket plotted by a computer.
First (see diagram below) he fired a short burst of backward burn from the thrusters, lowering Gemini's apogee by 13 miles. Almost 40 minutes later, he triggered a forward burn to raise the perigee ten miles. Next he yawed the spacecraft and fired the aft thrusters to move it onto the same orbital plane as the phantom. After one last forward thrust to raise the apogee, Cooper had his craft in a co-elliptical orbit with the phantom Agena—close enough so that the pilot, using on-board radar and computer, could eventually bring his craft to within 17 miles below and 38 miles behind the phantom. "Mission accomplished," announced the ground controllers. To have completed the terminal maneuvers, the astronauts would have needed an actual object to sight. "One of the biggest things we've learned," said Kraft, "is being able to pick a point in space, seek it out and find it. And it appears that we have a really good hack* on what we can do with Gemini 6 in getting the spacecraft in the right position to carry out the terminal phase of rendezvous."
Doctor's Orders. The astronauts tended to their equipment that floated about weightless. When they dumped urine overboard, the particles froze in the cold vacuum and sparkled like a roman candle as they drifted by. The men tried to nap. But when one stirred in the cramped quarters, the other woke up. "We don't like to see them so fatigued at so early a point in the flight," said Dr. Charles Berry, chief space-flight surgeon. The doctor's orders: Get more sleep. "I try to," yawned Conrad, "but you guys keep giving us something to do."
Usually Cooper was the taciturn, matter-of-fact command pilot, Pete Conrad the ebullient space tourist. On one pass he chattered with Astronaut Jim McDivitt, sitting as capsule communicator at Houston:
CapCom McDivitt: You sure do talk a lot.
Conrad: What do you want me to do, sing a song?
McDivitt: Think you can?
Cooper (interrupting): He sings off key.
Conrad (off key):
Over the ocean Over the blue Here's Gemini 5 singing to you.