HOUSTON (Reuters) - Astronauts aboard shuttle Discovery prepared to leave the International Space Station on Friday while ground control teams revamped landing plans to handle a small leak in one of the ship's power generators. Managers believe the leak is inconsequential but because there is not enough proof, they are proceeding cautiously. [snip] The shuttle has three power units needed to move the body flaps, speed brakes and other critical landing gear. It can safely land with just one, though two or more make for greater control, Shannon said. One unit has a tiny leak, about six drops per hour,...