The California Science Center in Los Angeles is moving forward with its plan to be the only museum to display its retired space shuttle in a full, upright "as launched" configuration.

To that end, the museum has announced that NASA has agreed to donate the only surviving huge external fuel tank, to be joined with the shuttle Endeavour along with two solid fuel boosters obtained earlier, allowing the science center to the display Endeavour in a vertical "full stack" launch arrangement.

The giant, orange external fuel tanks, more than 150 feet long, were the only major component of the space shuttle system not recovered and reused following launch; instead they were jettisoned and allowed to bun up in the Earth's atmosphere.

That had officials at the science center thinking they'd have to settle for creating a replica.

That's when NASA stepped in with its offer of the only remaining tank, a lightweight version different from the ones that sent shuttles on their way to the International Space Station.

That $75 million lightweight tank was intended for low-earth orbit shuttle missions, but in 2003 NASA reprioritized its mission program to complete the space station before retiring the shuttle fleet.

"We never flew another low-earth science mission," says Dennis R. Jenkins, the project director overseeing the museum's shuttle display and a former contract engineer on the shuttle program. "So this one tank sat there, waiting for a mission, and we never flew another mission that was appropriate for it."

NASA initially planned to put the tank on display at the factory where it was built, but the museum "made a better plea," he says.

"NASA thought it was a better use of the resource and gave it to us."

When the tank arrives in Los Angeles by barge, from New Orleans through the Panama Canal to Marina del Rey, it will be moved to the science center along city streets, following the route Endeavour took in 2012, a journey witnessed by huge crowds that gathered to watch the shuttle make its way slowly and carefully to the museum in downtown LA.

The museum hopes to have all the components - shuttle, tank and booster - together for the dramatic vertical display by 2018, says California Science Center President Jeffrey N. Rudolph.

"We are very excited," he says. "A lot of people at NASA see the value in having one place in the world where there could be the full space shuttle showing the full system in one place."

"In today's world, you can see anything virtually. Seeing the real thing is not so common anymore."