Protecting the spaceport has always been hard, but now it's going to be tougher, and visitors could face new restrictions to protect the shuttle fleet.

With untanned legs poking from Bermuda shorts, and sunglasses, a T-shirt and a backpack thrown over one shoulder, the man looks like any other Florida tourist.

He shows a $24 ticket purchased with no identification, walks through no metal detectors and hops on a crowded bus. Within minutes he's near some of America's highest technology - four space shuttles, parts for the International Space Station, two launch pads.

Carrying a bomb, he's intent on destroying the target of his choice and killing the bus' passengers - as many workers as possible - and himself.

This scenario used to be the stuff of worst-case drills at NASA's Kennedy Space Center, but after last week, officials know better: What was once a hypothetical threat is now a very real danger.

KSC, the mythic gateway to space, the place of the right stuff and an internationally known symbol of America's freedom and can-do spirit, is vulnerable to terrorism, and there is no guarantee the unthinkable won't happen here.

Protecting the spaceport has always been a challenge, but it's one NASA has accepted because the agency believes its work is inspiring, historic and must be seen up close by the public that funds it.

But, along with that comes the knowledge of what such openness could bring.

"We recognized that a smart, well-equipped terrorist could still get to you, and we always talked about that," says former shuttle launch director Bob Seick, who now serves on a NASA safety oversight panel for Congress.

Security, says Seick, "has been very well done, but when you look at the events of a couple of days ago, aside from having armed military airplanes flying over, there's not much you could do."

Jack Spencer, a terrorism expert at the Washington, D.C.-based Heritage Foundation, says he has no doubt the space center would make an attractive target.

"We don't know what's next on the list," he says.