Readjusting to gravity anti-fun for astronauts

— -- Astronaut Clayton Anderson is a four-sport athlete who loves to lift weights. But after his return to Earth, scheduled for today, he'll need help just taking a few steps.

He's been advised not to "go anywhere without having two people standing on either side of me," says Anderson, who has been living in space for the past five months.

If all goes as planned, space shuttle Discovery will bring Anderson home today at 1:02 p.m. ET. Also on board: six astronauts who blasted off on Discovery Oct. 23. The weather at the shuttle's Florida landing strip is expected to be good, flight director Bryan Lunney said.

The shuttle originally was supposed to touch down before dawn, but Discovery commander Pamela Melroy asked for a time change to make it easier for the crew to adjust their body clocks.

The change also means a shift in the shuttle's path. Usually the spacecraft passes over Central America and the Caribbean on its way home, but the shuttle today will glide across most of the United States and should be visible to those directly underneath it, Lunney said.

For the astronauts, coming home will be no joy ride. Among space-shuttle crews, common reactions upon return include dizziness and nausea. Studies show the ability of shuttle commanders to land the spacecraft also suffers because of the effects of re-entering gravity.

The longer a person has been in orbit, the more incapacitating the symptoms. So Anderson is in for a rough return.

"Coming back to Earth was a little bit painful," concedes Sunita Williams, who returned in June from six months on the station. "If I moved my head too fast, I wasn't feeling so good."

When astronaut Peggy Whitson was coming home from the station in 2002, she thought a crewmate had erred in saying they were incurring 1½ "g's," or gravitational forces. "I was sure he was misreading the dial. It just felt like a lot more than that," says Whitson, who is now on the station again.

Once back in the grip of gravity, blood puddles in the legs and feet. Because of the lack of blood flow to the head, some faint. Even shuttle astronauts may pass out.

"Things just start closing in on you," says astronaut Heide Stefanyshyn-Piper, who fainted twice in a hot room two days after landing in the shuttle in 2006.

Complicating the effort to stand after landing is the disorder of the inner ear, which helps humans balance and orient themselves. After returning from space, a slight head motion can induce vertigo and nausea. Some astronauts have illusions about which way they're moving and how much.

That can create problems for commanders, whose job it is to land the shuttle. The side effects of re-exposure to gravity cause delayed reactions and a decrease in the ability to track moving objects, says NASA flight surgeon Terrance Taddeo. As a result, commanders don't perform as well landing the spacecraft as they do in landing simulators.

Once on the ground, astronauts often complain of sore calf muscles and feeling so heavy that even taking a step is an effort. During his first night sleeping on Earth after six months on the station, former astronaut Ed Lu said he "felt glued to the bed."