The size of KSC is one reason that makes it hard to keep under tight guard.

The installation sits on 140,000 acres surrounded by the alligator-infested waters and swamps of the Merritt Island National Wildlife Refuge. It has 12,000 workers, $11 billion worth of space shuttles and billions of dollars worth of hardware for the space station.

KSC is protected by 250 security officers employed by Space Gateway Support, who also guard the adjacent Cape Canaveral Air Force Station.

That 15,400-acre facility is strictly off-limits because it's used by the Pentagon to launch most of its spy and communications satellites on unmanned Titan, Delta and Atlas rockets.

The guards are armed with semi-automatic pistols, submachine guns, M-16s and sniper rifles. They also have access to heavier weaponry.

During the 1998 shuttle flight that featured Mercury 7 astronaut John Glenn's return to space, NASA called in military Humvees equipped with machine guns and Stinger missiles, the latter of which can shoot down aircraft. Helicopter gunships also circled overhead.

While the man-made borders and surveillance gear are important, Seick says the harsh natural terrain should not be underestimated in helping deter would-be attackers.

"Alligators, water moccasins, mosquitoes that are too many to count, it's a good natural boundary," Seick says.

Despite such precautions, KSC and the Air Force station have suffered embarrassing security lapses that raise the possibility of potential disaster.

On July 6, 15 illegal Chinese immigrants came ashore undetected on the beach near a shuttle launch pad, taking cover under trees and brush for several hours until a patrol officer stumbled across them.

The group, led by a Jamaican smuggler, came by boat and apparently did not know where they had landed, officials say.

In late 1995, Cocoa City Councilwoman Phyllis Churchill surprised security forces when she was caught driving drunk around KSC and the Air Force station after attending a party. Guards stopped her when she approached them to ask for directions.

Meanwhile, anti-nuclear protesters have breached security at the Air Force station on several occasions.

In 1997, before the launch of NASA's plutonium-powered Cassini spacecraft to Saturn, military guards and Brevard County Sheriff's deputies rounded up 27 protestors who had slipped onto the Air Force station's grounds.

A decade earlier, an elderly woman got past guards and climbed a Titan rocket launch tower at the Air Force station during protests of test flights of the Navy's Trident 2 nuclear-tipped missile.

She went undetected for hours and finally picked up a phone at the launch pad and called guards to come and arrest her.

NASA and the Air Force decline to talk about their security operations, saying to do so would provide information to terrorists. However, both have recently been strongly criticized for allowing 16 civilian guards to be laid off in a cost-cutting move.

Since the terrorist attack Tuesday, officials have not said whether they may reconsider the layoffs or bolster the force even more.

The main focus of KSC security is placed on the irreplaceable shuttle fleet. At any given time, the ships are in their hangars, the giant Vehicle Assembly Building or at the launch pad.

The orbiters are arguably safest while out-of-sight in the hangars, where most pre-flight work is done. Guard posts staffed with armed officers and sophisticated identification card trackers keep tabs on everyone who goes in, such as workers and the occasional VIP.

The Vehicle Assembly Building - where the shuttles are taken to be connected to their twin solid booster rockets and massive orange external fuel tank - boasts similar safeguards.

Shuttle movement between the nearby buildings and the launch pads draws extra security. Three or four black-clad police officers armed with submachine guns walk beside the orbiter as it moves to the VAB. Helicopters keep a vigil overhead when it crawls to the launch pad.

The shuttles are most vulnerable during their first minute of launch and during their stay on the pad before blastoff, a period that normally lasts four to six weeks. While there, a shuttle is encased in a metal gantry, but its booster rockets and fuel tank are largely exposed.

That exposure is at the center of KSC's layered security approach at the pad.

"The closer you get to the launch facilities, the heavier the security gets," Calvin Burch, KSC security chief, said the day the Chinese immigrants were found.