Glenn gestures during a news conference Sunday in front of a 1962 picture of himself from his previous stint as an astronaut

SPACE CENTER, Houston (AP) -- John Glenn is back. And he's still NASA's guinea pig.

Up next for the world's oldest astronaut are three weeks of medical tests at Johnson Space Center related to his mission aboard the shuttle Discovery. He even had to climb back into a wired-up sleep suit Sunday night so that his post-flight slumber can be compared with how he slept in orbit.

There are more shots, too, and what he calls bloodletting -- he provided 17 such blood samples in orbit -- before he can return to his Washington-area home around Thanksgiving. Even then, he'll have to undergo monthly muscle and bone tests for six months.

More than 1,000 people packed a Houston airport hangar Sunday to greet Glenn has his fellow astronauts upon their arrival from Florida's Kennedy Space Center. Mayor Lee Brown told them their mission had "renewed an American love affair with space travel."

The astronauts, who seemed overwhelmed by the show of support, urged Americans to maintain an interest in the space program after this mission.

"Do not let the landing ... be the final chapter in this exciting adventure about space," said shuttle commander Curtis Brown Jr. "Instead, let it be the first chapter in a new adventure: the International Space Station."

Added Glenn: "I wish that every flight received this same kind of attention. Each flight deserves it."

Earlier, at his first post-flight news conference, Glenn said he was "95 or 98 percent back to normal," though he admitted he "didn't feel too hot" when he stood and walked off the shuttle Saturday after nine days of weightlessness.

"I was not disoriented, that would be too strong a word for it. But you're walking very spraddle-legged so you can keep your balance," he said.

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Asked how the mission stacked up against his history-making ride in 1962, when he became the first American in orbit, Glenn said, "I got great satisfaction the first time out of just being up there and being the first one to do this for our country. And here I am all these years later."

Saturday's smooth landing wrapped up a 3.68 million-mile voyage that took the shuttle around Earth 134 times. Glenn had been yearning to go back up since his first flight on February 20, 1962; NASA finally gave way in January, clearing him as the first geriatric test subject in space.

Glenn promised there will be no more space flights for him, but admitted his desire to return to space might never die.

"Obviously, we'd like to ... go right back up again, but that's not to be," he said. "And so a sense of accomplishment I guess I feel and a little bit of letdown that the whole thing is over, maybe, but nothing serious."