A massive space shuttle fuel tank is winding its way through the streets of Los Angeles Saturday, on a 16-mile trek heading to the California Science Center.

It's set to be displayed with the space shuttle Endeavour. The tank, which was never used in a mission, is the "last flight-qualified space shuttle external tank in existence," according to the science center.

As reporter Danielle Karson tells our Newscast unit, ET-94 weighs "66,000 lbs., and is as tall as a 15-story building."

Of course, there are plenty of logistical challenges in moving an object of this size through a crowded metropolitan area. As The Associated Press reports, the giant tank started moving at midnight from Marina del Rey, where it "arrived by barge Wednesday." It's crawling along at about 5 mph, the wire service reports, and is expected to take 13 to 18 hours to reach the science center.

Crews had to prepare the route in advance for the huge tank. As the Los Angeles Times reports, crews loosened "utility lines, street lights and traffic lights so they can be removed just before the fuel tank passes. They will be reinstalled immediately afterward."

It took 30 engineers to work out how to get the tank through Los Angeles — where "along with affecting 50 of the city's intersections, it will also have to make two epic turns," member station KPCC reports.

A Times infographic shows how the tank makes a turn. It's a slow process that involves eight crew members guiding the 32-wheel transport device.

The spectacle is drawing big crowds along the tank's route, where people are posting photos and videos using the hashtags #ETcomeshome and #ET94, among others.

Fans include these aspiring astronauts:

The tank delivered to NASA before the Columbia accident. After the Columbia shuttle was destroyed as it re-entered Earth's atmosphere, NASA scientists studied ET-94 to determine whether its design played a role in the incident. Today's ride is the last step in a long journey; it was shipped from New Orleans by barge, passing through the Panama Canal on its way to Los Angeles.

Los Angeles residents have actually recently seen another piece of NASA history cruising down their streets: The space shuttle Endeavour made a similar journey in 2012 (charmingly dubbed "Mission 26: The Big Endeavour"). At 122 feet, it was significantly shorter than the tank, which measures 154 feet.

The tank was donated by NASA, and Science Center President Jeff Rudolph tells Danielle that he's thrilled to acquire the tank.

"As soon as we got Endeavour, we said we got to see if there's any way we can get that one remaining external tank," he says. Danielle adds that the center is hoping to eventually add booster rockets to the display.

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