Shuttle Atlantis on the launch pad at sunsetAtlantis Launch Notes: July 6, 2:45 P.M.

KENNEDY SPACE CENTER--One day, 20 hours to launch on Friday. This may be a last for the shuttle program, but it's a first for me. I’ve watched liftoffs since Alan Shepard took his ride—but only on TV or the Internet. As any NASA explorer would know, a first foray into new territory involves a learning curve. Visiting a sprawling complex like this involves a series of wrong turns, waits for credential checks and trying to figure out just where one is supposed to go, and—even more important—NOT go. That is, if you don’t want to lose your press pass. Like most government installations, security is courteous, necessary and as ubiquitous as the air. Reporters must be escorted everywhere (although you don’t need a minder for the cafeteria, if you can find it). I’ve given up putting my ID back in my wallet. But I look outside, and there it is out there, the voluminous Vehicle Assembly Building where they mate the shuttle to its fuel tank and solid engines. And it is also the place where they put together Saturn 5s for NASA's storied lunar missions.

Right now the countdown continues. But a tropical front is bearing down on the Florida peninsula, and the most optimistic assessment by the Mission Management Team in charge of giving Atlantis a go/no-go for its Friday launch date is 30 percent. A final decision will be made as to whether to proceed with fueling—a lengthy process that would be wasted if the weather situation deteriorates. As I type this, I hear reporters debating among themselves, with veterans of previous launches saying that all they need is a “hole in the clouds” to get STS 135 up and into orbit. With all the planning and precision engineering and physics, it all comes down to the luck of the draw. The good news is that as it stands now, Atlantis and crew are ready to fly. If there is a delay, and the shuttle has to be refueled, it will probably be 48 hours until the next try.

Image: The sun rises over the Atlantic Ocean, silhouetting space shuttle Atlantis's external fuel tank and solid rocket boosters on Launch Pad 39A at NASA's Kennedy Space Center in Florida. Image courtesy of NASA.