LOS ANGELES, Calif. -

The space shuttle Endeavour, which has flown nearly 123 million miles, set out this morning on what should be its final journey -- a laboriously slow 12-mile trek from LAX to its retirement home at the California Science Center in Exposition Park.

It began rolling out of a hangar at the airport around 11:30 p.m. Thursday, said Mary Grady of Los Angeles World Airports, which operates LAX.

After a minor mechanical glitch affecting the transport vehicle delayed its scheduled 2 a.m. departure, Endeavour, sitting atop a high-tech flatbed carrier, left the airport at 2:15 a.m. today, a Science Center volunteer said.

The 2-mile per hour trip is being referred to by organizers as "Mission 26," since the orbiter completed 25 space missions. The shuttle's tiles are waterproof, so rain along the route will not slow the mission down, said Ken Phillips, the Science Center's curator for aerospace science.

By 5:45 a.m., Endeavour reached its first scheduled stop, a parking lot at the intersection of La Tijera Boulevard and Sepulveda Eastway, where it will remain until 1:30 p.m..

NASA announced in April 2011 that Endeavour would be permanently housed at the Science Center -- returning to the region where it came into being. It was built in Palmdale starting in 1987 to replace Challenger, which exploded 73 seconds after takeoff on Jan. 28, 1986.

Endeavour made its first flight May 7, 1992, and completed its final space mission on June 1, 2011, having flown 122,883,151 miles in 4,671 orbits around the Earth.

Organizers say that working out the route from LAX to the Science Center required a degree of planning worthy of a space mission, and though this journey is taking place on terra firma, parts of it will be harrowing, with the orbiter's 78-foot wingspan and five-story height taking its fragile tiles to within inches of buildings at various points along the way.

Before the shuttle could be transported through city streets, crews removed 268 trees and trimmed another 265 within Los Angeles city limits. The city will plant at least 702 trees to make up for the lost ones, officials said.   Additionally, 128 trees were removed in Inglewood and are to be replaced by twice that number.

Plans also called for crews from L.A.'s Street Lighting, Transportation and Water and Power departments to temporarily remove 222 street lights, 63 traffic signals, 35 power poles, 11 parking meters and two overhead signs.

Endeavour will do the bulk of its travel along Manchester, Crenshaw and Martin Luther King Jr. boulevards. Its weight -- 151,205 pounds -- is too much for the roads on some parts of the route, so engineers installed 2,180 steel plates to support the weight of the shuttle plus its transporter.

Crews began closing streets to accommodate the shuttle's move as early as 10 p.m. Thursday. The shuttle is expected to arrive at the Science Center around 8:30 p.m. Saturday.

Authorities said streets and sidewalks will be closed along the shuttle's route. However, three public viewing events are scheduled for Saturday.

Around 8 a.m. Saturday, the shuttle will stop in front of the Forum in Inglewood. Parking for spectators will be available at the Hollywood Park Race Track, which officials said would open at 4 a.m. Saturday.

Around 2 p.m. Saturday, Endeavour's drivers will stop for another 30 minutes at the intersection of Crenshaw and Martin Luther King, Jr. boulevards.

That stop includes speeches by city officials and a performance by the Debbie Allen Dance Academy.

Large parking lots have also been dedicated for the public to get a glimpse of the orbiter as it rolls into the Exposition Park area Saturday night, including four lots between Bill Robertson Lane and Vermont Avenue north of Martin Luther King, Jr. Boulevard.

The Los Angeles Police Department warned those hoping to catch a glimpse of the shuttle to expect large crowds and heavy traffic. Police Chief Charlie Beck said nearly 700 cadets and volunteers will be on hand during the trip to help keep things moving safely.

The Los Angeles County Metropolitan Transportation Authority on Saturday will be running additional Metro rail service trips to Exposition Park, which is served by two stations at Expo/Vermont and Expo Park/USC.

Bus service in the areas along the shuttle route will experience disruptions during Endeavor's final trip, according to Metro spokesman Marc Littman. Service detours are planned along Manchester Boulevard on Friday night and Crenshaw Boulevard and Martin Luther King Jr. Boulevard on Saturday.

To accommodate those wishing to see the Shuttle move into its new location, Metro's Expo Line will run at 6-minute intervals from 2 to 11 p.m. Saturday. Metro Red, Purple and Gold Line trains will run with extra cars at 10-minute headways from 2 to 11 p.m. Metro staff will also be stationed along the Expo line at Union Station and the 7th/Metro Station to assist with transfers, fare purchases, directions and information on bus detours.

Those who can't make it to see the shuttle on Saturday will only have to wait 17 days to see it up close. The Science Center's Phillips said the shuttle will be on public display beginning Oct. 30.