"The United States stands alone with just one other nation that can launch humans into space, and that's something that every American should be really proud about," Kelly said.

"We're going to be excited, and we're really hoping that the rest of the nation is going to be excited about our launch as well."

Tight security

Look for military jet fighters and helicopter gunships to be patrolling Central Florida skies as countdown clocks tick toward a planned 7:41 p.m. EST (0041 GMT Friday) liftoff.

An expansive "no-fly zone" surrounding NASA's coastal Florida spaceport will be strictly enforced so that no would-be terrorist -- or wayward private pilot -- approaches within 34.5 miles (55.2 kilometers) from the shuttle's launch pad.

Surface-to-air systems equipped with Stinger missiles reportedly are in place, and light anti-aircraft guns also might be set up in the Cape Canaveral area.

Sea-based security forces also will be in position, cruising through an Atlantic Ocean security zone off the east-central Florida coast.

Heavily armed SWAT teams will be on guard, and all those at KSC -- journalists, VIPs and even NASA and contractor workers -- will be subjected to stepped-up identification checks and random searches.

All in all, the heightened security measures will eclipse those in place for Cold War-era moon missions, the much-ballyhooed return to space of John Glenn in 1998 and past presidential visits.

Said Col. Sam Dick, vice commander of the Air Force's 45th Space Wing, the military unit responsible for launch-day security: "We have taken unprecedented but critical steps to ensure all reasonable measures are in place to protect the shuttle and its crew from any security threat, whether from land, air or sea."

Countdown ritual

The Endeavour astronauts, meanwhile, will don partial pressure flight suits at KSC crew quarters and then depart for launch pad 39B about 3:51 p.m. EST (2051 GMT).

A traditional crew departure photo opportunity has been scraped for security reasons, and helicopters will escort NASA's "Astro-Van" to the launch pad.

Six U.S. astronauts and a Russian cosmonaut will begin boarding Endeavour about 4:21 p.m. EST (2121 GMT). Among them: Yuri Onufrienko, Daniel Bursch and Carl Walz, a trio that will serve as the fourth full-time crew of the international station.

Nestled in the shuttle's cargo bay: An Italian moving van filled with 3.5-tons of food, water, supplies and scientific equipment for the Expedition Four crew, a group that plans to live and work on the station until next May.

Three dozen Japanese quail eggs and 24 laboratory mice also will be making the round trip to the station, the subjects of embryonic development and osteoporosis research, respectively.

But a much more symbolic payload also will be flying aboard Endeavour.

Some 10,000 small American flags will be hauled to the station and then brought back to Earth to pay tribute to those who lost lives when terrorists crashed hijacked airliners into the World Trade Center in New York, the Pentagon in Washington, D.C., and rural Pennsylvania.

About the size of large postcards, the flags will be mounted on special certificates and distributed to the families of Sept. 11 victims.

The shields of 23 New York City police officers lost in the attacks also are onboard along with 91 NYPD patches. From the Fire Department, City of New York: A large FDNY flag and a poster bearing the pictures of the 343 firefighters killed as a result of the World Trade Center attack.

A Marine Corps flag that was recovered from the Pentagon and an American flag that was flying over the state capitol in Pennsylvania on Sept. 11 also are tucked away in Endeavour, along with a U.S. flag that was recovered from the rubble at Ground Zero.

Endeavour commander Dom Gorie said the Trade Center flag was remarkably intact.

"It has two small tears and you could smell the strong aroma of ashes. It's a very, very strong symbol that this flag survived, and it's going to fly to the highest place we can fly it," the veteran astronaut said.

"We're going to give it a really, really great ride, and it's not going to take much to return it to its former beautiful state. And it'll fly again some day."

Flight plan

Assuming all goes well, Endeavour is scheduled to arrive at the station Saturday. Anxiously awaiting its arrival: Current station commander Frank Culbertson and two cosmonauts, Vladimir Dezhurov and Mikhail Turin.

The shuttle will remain at the station for a week while incoming commander Onufrienko and flight engineers Bursch and Walz move in to the outpost.

Culbertson and his colleagues, meanwhile, will be packing up to return to the same planet -- but a much different world -- than they left four months ago.

The only humans living off Earth on Sept. 11, the Expedition Three crew videotaped the billowing cloud of smoke created by the collapse of the two 110-story World Trade Center towers, and they witnessed the resulting shutdown of U.S. airlines, evidenced by an eerie lack of contrails in American skies.

They've kept track of the resulting war on terrorism through daily news reports beamed up from NASA's Mission Control Center, but they've yet to experience post-Sept. 11 life on Earth.

"There are a lot of changes, according to our families, down there on Earth that I think we're going to have to get used to," Culbertson said in a recent interview. "Life is different now, and we will take some time to acclimate."

Gorie agreed.

"I think all of us in the United States have been affected a great deal. We probably don't even realize how much we have been affected. And I think for Frank and his crew, they haven't been part of that," the shuttle skipper told SPACE.com.

"They haven't seen it on an hour-by-hour basis almost every time they turn on the television. They haven't been aware of the people -- their neighbors and their friends -- that are losing sleep," he said. "I think they are going to realize that things have happened that will change their lives, as well as ours, forever."

Endeavour and the Expedition Three crew are due back on Earth Dec. 10.