After taking a phone call from President Barack Obama, the Discovery astronauts and their space station colleagues transferred spacesuits and equipment back to the shuttle and took the afternoon off before a busy day Wednesday completing final transfers and undocking from the international lab complex.

The presidential phone call "was a special treat for the crew," lead Flight Director Kwatsi Alibaruho told reporters. "That downlink event went very well and I know both the president and his guests, as well as the crew, I'm sure they all enjoyed that."

On the eve of undocking, the astronauts were about 78 percent complete with work to transfer equipment and experiment samples from the station to the shuttle for return to Earth. The most critical return items - frozen biological samples and 4 to 5 liters of water from the station's new urine recycling system - will be transferred Wednesday.

Visiting shuttle astronauts normally finish transfers and close hatches between the shuttle and the station the day before undocking to make separation day a bit less rushed. But to protect against the possibility of weather delays, NASA managers decided to wait until the last minute to close the hatches this time around to make sure the experiment samples, some stored in a shuttle freezer and the rest in double cold packs, have a sufficient shelf life.

As a result, flight planners gave the astronauts a second half-day of off-duty time today.

"With all the spacewalks we've done and all the assembly activities, they've had a limited amount of time just to kick back and share experiences, both the Discovery crew and the space station crew, share their experiences with each other and just have some time for fellowship," Alibaruho said. "So, that's something they were able to do today that they very much enjoyed.

"Tomorrow will be a busy day of course. We'll start with the packing of some of the last items of cargo that are going to be transferred from the space station to the shuttle. That includes some of the scientific samples that are going to be coming back in those double cold bags we talked about earlier. The crew will also take the final water samples that we have from the WRS, the water recovery system, so those samples can be returned home and examined to perhaps clear the system for use by a six-person crew."

Under the revised flight plan, the two crews will gather for a brief farewell ceremony in the Harmony module around 1 p.m. before closing hatches between the two spacecraft and carrying out leak checks. Undocking is targeted for 3:53 p.m. Shuttle pilot Dominic "Tony" Antonelli plans to guide the shuttle through a complete loop around the station, giving engineers and the public a look at the lab's now-complete set of solar arrays.

"They'll take pictures of the space station so we can see how it looks with all of its solar arrays completely unfurled and in a symmetric configuration," Alibaruho said. "The shuttle will execute separation burns and move to a lower orbit where it will remain for a day or so in preparation for landing on Saturday at the Kennedy Space Center."

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