Animation shows Leonardo being lowered back into Endeavour's payload bay. Photo: NASA TV/Spaceflight Now

The day after the final spacewalk, Cockrell is scheduled to remove the Leonardo cargo module from Unity's nadir hatch and re-berth it in Endeavour's cargo bay for return to Earth. Undocking is scheduled for the next day, on flight day 11.

"It's basically a reversal of the process of what we did when we docked," Lockhart said in a NASA interview. "You know, when we docked, we came together and then we had to go through a series of steps in order to attach the two pieces together. Well, we've got to reverse that.

"There's a series of springs that actually push the orbiter away from the station. And then, I will start to fly the orbiter away from the station. I liken a little bit of this and the rendezvous a little bit to air-to-air refueling in aircraft, which some people may realize we have two vehicles that are moving at a high rate of speed, but their relative velocity is really low.

"But it's never stable," he said. "In other words, it's not like this one vehicle is parked and this vehicle is parked. It's always a constant maneuvering between the two. And so, when you dock and when you undock, it's the same thing. You get a separation but immediately, you have orbital mechanics effects start to take effect. ... So I have to keep making inputs in order to maintain the axis that I want to separate on."

After backing away to a point about 450 feet directly in front of the station, Lockhart will guide Endeavour through a lap-and-a-quarter fly-around of the station for routine photo documentation. The shuttle crew then will leave the area and the astronauts will prepare for entry on June 11.

As with all returning long-duration station crews, Onufrienko, Bursch and Walz will make the trip back to Earth resting on their backs in recumbent seats bolted to the floor of the shuttle's lower deck.

Perrin, who made the climb into space seated on Endeavour's upper deck, will be strapped in on the lower deck for entry to assist the station crew, if needed, as they re-adjust to the unfamiliar tug of Earth's gravity.

Based on recent experience, however, his help likely won't be necessary.

"Our crews are coming down in a lot better shape than we anticipated, maybe better than what they had returned to Earth after the shuttle-Mir missions," Whitson said.

"We do think our exercise protocols are working very well, in particular resistive exercise," she added. "I think they've seen less bone loss in those crew members who've been doing more resistive exercise. We have taken the initial steps and we know some of those steps are effective and so I think we will be continuing the exercise program as much as we can feasibly conduct it."

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