As if they were performing delicate surgery, a crew inside the California Science Center museum hoisted a 3,000-pound portable space lab and storage pod inside the space shuttle Endeavour's huge cargo bay Thursday, reuniting the retired orbiter with a piece of equipment it used on some missions over its two decades of flight.

It was just one small step that, along with the installation of a replica robotic arm, airlock and docking system, moves the last shuttle ever built closer to becoming the nation's most complete iteration of the grounded aircraft on exhibit.

None of the other shuttles on display have equipment in the cargo bay. Endeavour's final pose will also be unique: It will be the only one of the three retired shuttles that orbited the Earth Endeavour, Atlantis and Discovery to be posed with its nose pointing to the stars, just like when it flew into space.

The final exhibit is still four years away from being complete. But the installation of equipment, which will continue in the coming days at the temporary exhibit site, will offer the public a rare, brief chance to see Endeavour with both cargo bay doors open before they are closed after Oct. 21.

The cargo bay is so enormous a school bus can fit in it a scale most people have not been able to appreciate because the cargo bay doors were almost always closed when in public view on Earth. At its technologically awesome heart, the shuttle was a workhorse.

"That's what this thing is about bringing stuff to and from space," said California Science Center president Jeffrey Rudolph. "So that's why we really wanted to be able install a payload and put it up, and let people understand the function of the space shuttle a lot better."

When the final exhibit at the yet-to-be built Samuel Oschin Air and Space Center is unveiled, visitors will get to see two views of the shuttle.

The plan is for people to first watch a movie about Endeavour before the screen rises, allowing guests to see the shuttle vertically.

"Just like it's ready to launch," Rudolph said. Walking to the other side, people will be able to peek inside the craft.

"That payload bay door will be open, and you'll be able to look inside," he said, and get a view of the laboratory and storage pod, named Spacehab. Visitors will be able to walk underneath the massive engines.

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Space shuttle Endeavour inches closer to completion of final exhibit