The Museum of Flight's Space Shuttle Trainer exhibit opens to the public Saturday, with a ceremony planned at 11 a.m. Built in the 1970s, the trainer was used by the crews of all 135 NASA shuttle flights over three decades.

Please don’t use the plastic toilet.

On Saturday, the public will get its first chance to see the completed Space Shuttle Trainer Exhibit at the Museum of Flight.

Presentation of the wingless, wooden trainer, which Seattle got from NASA in lieu of an actual space shuttle, caps more than a year and a half of planning and preparation that included bringing the mock-up from Houston — in pieces.

Crews for all 135 space-shuttle missions, from 1981 until the program ended last year, trained in the mock-up, which still bears scuff marks made by the boots of astronauts as they rappelled down the trainer in evacuation drills.

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The first thing visitors may notice about the trainer is that it’s huge — 122 feet long and rising, at its tail, 48 feet above the museum floor.

Visitors will climb 15 steps (or use a wheelchair lift) to enter the trainer’s 60-foot payload bay. Inside, they’ll pass under a replica of a Boeing-built booster rocket.

They’ll peek through round hatches into the crew compartment — a cramped, hard-to-reach section open only to special tours.

And if these visitors are like others at the museum, no aspect of living and working in space will prompt more curiosity than how astronauts … uh … took care of their personal business.

“It’s always the number one topic,” said Chris Mailander, the museum’s director of exhibits.

Because the trainer’s toilet is out of sight in the crew compartment, a plastic full-scale replica has been set up outside the trainer. A nearby panel tells how the “Waste Collection System” works. Suffice to say that in the low-gravity environment of space, “airflow” helps get the job done.

At other displays, visitors will operate flight sticks to “land” a shuttle, and explore panoramic images from inside the trainer and a real shuttle.

While the myriad switches and dials in the trainer weren’t active, they gave astronauts a feel for how things were arranged in an actual shuttle.

Granted, this is not the piece of space history Seattle had hoped to land.

The Museum of Flight’s $12 million Charles Simonyi Space Gallery was built in the hope that Seattle would get one of NASA’s four retiring space shuttles — sought by more than 20 museums and visitor centers across the country.

But early last year, NASA Administrator Charles Bolden awarded the shuttles to museums in New York, Los Angeles, Florida and the Washington, D.C., area, saying that’s where the greatest number of people would see them.

The first shuttle that was relocated — Discovery — is already proving its potency as a visitor draw, attracting more than 977,000 visitors since it was placed in April in a Smithsonian Institution museum. That’s nearly a 30 percent boost in attendance from the same period last year.

It remains to be seen whether a faux-shuttle can have similar impact here.

This year, with the Museum of Flight getting a publicity boost from the trainer’s arrival, attendance is expected to top 500,000 for the first time. Museum President and CEO Doug King said he’s hopeful the exhibit will help send attendance even higher next year.

King insists the trainer can be a more effective teaching tool that an actual shuttle, because visitors can go inside it. The real shuttles must be displayed out of reach.

The trainer was built in the 1970s at the Johnson Space Center in Houston, the only home it knew before this year, when it was cut into pieces for the move to Seattle.

The Museum of Flight spent $1.85 million to have the sections shipped here and another $1 million to reassemble them and create the exhibit.

A sobering display near the rear of the trainer tells of the shuttle program’s two disasters, which claimed the lives of 14 astronauts.

Included are flight-training suits provided by families of two Washington state astronauts lost: Dick Scobee, a graduate of Auburn High School, who died in Challenger in 1986, and Michael Anderson of Spokane, in Columbia in 2003.

Jack Broom: 206-464-2222 or