The Crew Access Arm and White Room that astronauts will use in 2017 to board Boeing's CST-100 Starliner saw some of their first visitors Dec. 10 during a tour of the structures by the first four astronauts selected to train for Commercial Crew Program flight tests. Destined for attachment to the Crew Access Tower at Space Launch Complex 41, known as SLC-41, at Cape Canaveral Air Force Station in Florida, both the arm and White Room provide vital support for America's coming return to human space launches from the United States.

"The White Room is the last place on Earth you see before you get onboard the ship," said Commercial Crew astronaut Eric Boe, "so it really makes a big difference how it's outfitted because you're thinking about the last things before you lift off the planet and it's obviously a place where you make the transition from being on Earth to getting ready to go into space."

Wider than the space shuttle-era White Room, the new White Room is tailored to the design of Boeing's CST-100 Starliner, which will launch on a United Launch Alliance (ULA) Atlas V rocket. The spacecraft will carry four astronauts to the International Space Station, along with a small supply of cargo and equipment. The Starliner and SpaceX's Crew Dragon are being developed in partnership with the Commercial Crew Program to fly astronauts to the station and restore America's ability to launch astronauts from its own soil.

"Part of this visit was to just say thank you to all the folks who have worked so hard to get us to this point," said Commercial Crew astronaut Doug Hurley. "Then the other part is just to look things over and make sure it kind of looks like what we're familiar with or if they've made improvements, how that's going to work in the concept of operations for us getting into the vehicle. So, it looks great and they've made a lot of progress since last time we were down here."

The steel Crew Access Arm and aluminum White Room together reach about 50 feet and weigh about 90,000 pounds. They currently are at a construction yard where they were built, near NASA's Kennedy Space Center. Mounted to a test stand identical to the top levels of the Crew Access Tower, the arm and room will go through months of mechanical testing before being trucked to the ULA launch pad and lifted into place on the tower.

An environmental seal also will be added the end of the White Room to fill the gap between the spacecraft and white room and provide for a pressurized clean room around the Starliner hatch. A mock CST-100 has been put in place as it would at the launch pad to complete the evaluations.

Once tested and moved to the pad, the arm will act as a bridge from the tower to spacecraft at the top of the rocket, almost 200 feet above the launch platform.

"I think what's really important about seeing different parts of the whole thing coming together is you appreciate all the work that's going into this," said astronaut Suni Williams. "This is a lot of folks out here and also the subcontractors have been working very hard to make sure the product is what we have envisioned in our mind and I think it definitely exceeds expectations. So step by step, each piece, you understand how important it is to put together this whole program."

White Rooms are a longstanding fixture of human flights into space by NASA. They are basically clean rooms that prevent contaminants such as dirt, dust or stray hair from getting inside a spacecraft where, in zero-gravity, the contaminants could float up and jam behind instrument panels or be inhaled by astronauts.

Although a bit cramped because of the bulky pressure suits astronauts wear at launch, white rooms also have enough space for a few ground support team members who help the astronauts climb aboard the spacecraft and make sure everything is perfect for liftoff.

The White Room and Crew Access Arm also provide an escape route in the unlikely event of an emergency while the astronauts are at the launch pad.

"It's really important to see the White Room come together, to see the path you're going to have to take if there is an emergency egress and all those things," said Commercial Crew astronaut Bob Behnken.

"It's really difficult to just extrapolate them from a PowerPoint slide or somebody telling you just do this or just do that and then you'll see this thing and just do the next thing. It's really difficult to visualize all that but to get a chance to see it in person and walk through your actions just like when you get into the vehicle or get out of the vehicle is always important."

The other new, critical component of the launch pad also enjoyed time in the spotlight when the astronauts joined employees and managers from several companies for a "topping off" ceremony for the Crew Access Tower which is nearing completion at SLC-41. Standing about 200-feet-tall, the Crew Access Tower was built for Boeing and ULA by Hensel Phelps and numerous other companies. It was erected in modular sections that had been built four miles away and outfitted with stairs, cable trays and other fixtures. Stacking the segments between Atlas V launches, workers were able to assemble the main tower in about three months.

Following a long-held tradition in building construction, employees and guests were asked to sign the last beam before it was lifted into place and bolted to the top of the tower.

"Today you are part of history," said Kathy Lueders, program manager of NASA's Commercial Crew Program. "Stop and enjoy this moment. I hope everyone has been able to write their name on the beam because you are part of the critical safety network that is making this all possible."

Workers continue adding more steel platforms to the side of the tower to complete the design that was tailored from the start to the unique needs of astronauts who will traverse the structure wearing pressure suits and who may have their vision hindered by helmets and visors. That means walkways are wider than usual, corners are not as sharp on stairwells and all the edges on the structure are sanded smooth to prevent snagging spacesuits.

"We've poured 1,000 cubic yards of concrete and mounted nearly 1 million pounds of steel, and we've done it in spectacular fashion," said Howard Biegler, launch operations lead for ULA's Human Launch Services.

With the tower rising and Crew Access Arm and White Room coming together for SLC-41 launches, plus SpaceX's advances on its launch facility a few miles north at Launch Pad 39A, the astronauts said the impending return to spaceflight gets more exciting by the day.

"It's really exciting to be here and imagine that before too long we'll actually be walking through here with our spacesuits on," Williams said.