"We're all well aware that for over 200 years, and certainly over the last two months, freedom has rung loud and clear across this country. But right here, right now, it's time to let freedom roar," Endeavour commander Dom Gorie said. "Let's light 'em up."

With its three main engines and two boosters igniting in a white hot flash of light, Endeavour trailed an orange-tinged umbilical of smoke and water vapor as the ship arced out over the Atlantic Ocean and sped toward orbit.

Two minutes later, its twin boosters jettisoned on time, peeling away from Endeavour as the shuttle continued a majestic climb. The reusable rockets twinkled and flashed in the twilight sky as they tumbled toward the ocean, where twin recovery ships awaited their splashdown east of Jacksonville, Fla.

The shuttle could be seen streaking through evening skies along most of the U.S. eastern seaboard, and as far north as New York City. NASA flight commentator Rob Navias called the ship's ascent "flawless."

Coming two days after the Bush Administration issued a new nationwide terrorism alert, the shuttle launch occurred amid heightened security.

Ships and boats were shooed out of a security zone off the coast of Cape Canaveral by U.S. Coast Guard cutters and military surveillance aircraft, and an Air Force F-15 fighter intercepted a private aircraft that wandered into restricted air space surrounding NASAs spaceport.

The expansive "no fly zone" was established by the Federal Aviation Administration to keep aircraft from flying within 35 miles (56 kilometers) of NASAs twin shuttle launch pads.

Identified as a single-engine Piper, the intruding aircraft skirted the western edge of the no-fly zone and was escorted to an airport in Sanford, which is located north of Orlando.

Col. Sam Dick, vice commander of the Air Forces 45th Space Wing, the military unit responsible for shuttle launch-day security, said the aircraft came no closer than 24 miles (38.5 kilometers) of Endeavour and was traveling away from the shuttle rather than toward the ship.

"We determined quickly, by the action that Col. Dicks guys took, that it was not a threat to the vehicle," Leinbach said. "We would have been prepared to act had we received that further word, but it never got anywhere near us really."

The plane was spotted by advanced air surveillance radar put in place to keep tabs on private and commercial air traffic in central Florida. A private helicopter also had been intercepted by an Air Force F-16 Tuesday after inadvertently, but innocently, straying into the "no-fly" zone.

Neither Air Force nor NASA officials would say whether any specific or credible threat ever had been made against Endeavour. But a shuttle nonetheless is considered a potential target.

Standing 18 stories tall on a beachside pad, the shuttle is loaded with 500,000 gallons of highly explosive rocket fuel prior to launch, making the ship inherently vulnerable to a suicide attack in even a light aircraft.

Hijacked commercial airliners were used as fuel-laden weapons in the Sept. 11 attacks, and Air Force officials have noted that many of the terrorists involved had lived, worked and attended flight school in Florida.

The national alert issued Monday, meanwhile, served to point up the need for extraordinary security measures.

"In a lot of ways, it verified that what were doing is needed and appropriate," said Air Force wing spokesman Maj. Mike Rein.

The only real threat to launch Wednesday came from rain showers and thick clouds that hung over the Atlantic and began moving toward KSC. Stiff winds at NASAs shuttle runway also were a concern, but the weather proved to be acceptable for launch.

Six American astronauts and a Russian cosmonaut, consequently, now are streaking toward a planned docking at the station on Friday.

Cruising aboard Endeavour are Gorie, pilot Mark Kelly, mission specialists Linda Godwin and Dan Tani, and their three station-bound passengers: Yuri Onufrienko, Daniel Bursch and Carl Walz.

Anxiously awaiting their arrival: current station skipper Frank Culbertson and his two Russian colleagues, Vladimir Dezhurov and Mikhail Turin.

In space since August, the three men asked for frequent updates during the shuttle launch countdown, taking close note of the Florida weather during a pass over Cape Canaveral about 30 minutes prior to liftoff.

"Well, it does look like the only clouds in that part of Florida that are a little worse than scattered to none are right over the Cape. But they look very thin to us," Culbertson radioed down to NASA's Mission Control Center in Houston.

"Yeah, Frank. I think they look pretty thin to the commander sitting in the seat right now as well," astronaut Bob Curbeam replied.

Endeavour is speeding toward the station with 3.5-tons of food, water, supplies and scientific equipment for incoming outpost commander Onfrienko and flight engineers Bursch and Walz, who plan to live and work on the station until next May.

Thirty-six Japanese quail eggs and 24 laboratory mice will be making a round trip to the station aboard the shuttle, the subjects of embryonic development and osteoporosis research, respectively.

But a much more symbolic payload also is flying aboard Endeavour.

Some 10,000 small American flags are being flown to pay tribute to those who lost lives when terrorists crashed hijack 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 after Endeavour returns to Earth.

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 flew 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 World Trade Center rubble.

Endeavour's shuttle astronauts plan to remain at the station for eight days, helping the new crew move in and the old crew move out. Most of that time will be spent unpacking, and then reloading, an Italian moving van now nestled into the shuttle's cargo bay.

Godwin and Tani also aim to perform a spacewalk next Monday to fix a balky motor drive on the station's massive American solar wings, which stretch 240 feet (73 meters) from tip to tip.

With Culbertson, Dezhurov and Turin in tow, Endeavour is scheduled to depart the station Dec. 14, heading off on a two-day trip back to Earth. The shuttle is scheduled to land back here at KSC on Dec. 16, capping a 128-day stay in space for the Expedition Three crew.