The assembly of an upright, launch-ready display of the space shuttle Endeavour at the California Science Center drew one step closer to completion Saturday, as crews attached a massive external fuel tank to the Solid Rocket Boosters in the exhibit’s permanent location.

Crews at the Science Center began lifting the 65,000-pound tank, known as ET-94, around 8 p.m. Thursday, but the operation was delayed by winds. Thursday night and during Friday’s early morning hours, crews were able to attach the tank to a large construction crane, which lifted ET-94 vertically and over a wall of the under-construction Samuel Oschin Air and Space Center, which will house the one-of-a-kind shuttle display.

The 26-hour ordeal came to a close at 11:05 a.m. Saturday, when the tank was finally nestled between two 149-foot tall rocket boosters that have been in place vertically since early December, spokeswoman Maura Klosterman-Vu said.

It is the penultimate step in creating the world’s only authentic, ready-to-launch space shuttle system display. The final step will be to move, lift and attach the star of the attraction, Endeavour itself, later this month, Klosterman-Vu said.

On Wednesday, a “self-propelled modular transporter” was used to slowly move the large orange tank approximately 1,000 feet through Exposition Park and into position for its crane ride. It took roughly two hours to move the massive tank, which is 154 feet long and nearly 28 feet in diameter.

ET-94 is the last remaining flight-qualified external tank in existence.

The twin rocket boosters that were installed upright in December are each 149 feet tall, including the aft skirts — or base — of the boosters, along with the 116-foot-long rocket motors and the “forward assembly,” or cone-shaped tops.

The Endeavour had been on display horizontally at the Science Center for more than a decade. Public access to the shuttle, however, ended on Dec. 31 so preparations could begin for its eventual move to the new exhibit, which will be the only launch-ready display of a former NASA space shuttle in the world.

Science Center officials have dubbed the monthslong effort to create the vertical shuttle display as the “Go For Stack” process.

The shuttle launch display will be the centerpiece of the 200,000-square-foot Samuel Oschin Air and Space Center, which will nearly double the Science Center’s educational exhibition space. The building will include three multi-level galleries, themed for air, space and shuttle. The new facility will also house an events and exhibit center that will be home to large-scale rotating exhibitions.

An opening date for the $400 million center has not yet been determined.