The memory lives somewhere deep inside him, a place where it still pains him to go. The Challenger had exploded only days before, and Tom Henricks, a rookie astronaut yet to make his first flight, was heading to an apartment building in Houston for a grim task.

He and a senior colleague, an astronaut designated as a family escort before the flight, opened the door and stepped inside. The apartment was the home of one of the Challenger astronauts, and Henricks was there to follow the instructions that his fellow space explorer had left in the event of the unthinkable.

"It was emotional," Henricks says. But he stops himself, unable to continue.

The rest, he says, he will keep to himself, an artifact of the deeply emotional and closely held bond among the tiny cadre of men and women who get to call themselves astronauts.

Maybe it is the danger that draws them so close, some former astronauts say. Maybe it is the long hours and the rigors of training, or a shared sense of responsibility. Whatever it is, they say, something powerful and enduring happens when they first put on spacesuits together.

It is a camaraderie that seems to transcend eras. Astronauts who soared to new heights as the Beatles topped the charts mourned this weekend alongside colleagues half their age while the nation watched another shuttle -- this time Columbia -- fall to Earth in pieces.

On the bases where the astronauts train, lives inevitably intertwine. No one understands an astronaut as well as another astronaut, said Winston E. Scott, who went into space aboard Columbia in 1997 and is now a professor at the Florida State University College of Engineering.

Their work can isolate them, Scott said, drawing the astronauts tighter to one another. When it comes time to blast past Earth's atmosphere, they have rituals all their own.

One of the most sacred is the designation of escorts. Each crew chooses two astronauts to accompany their families to launches and touchdowns. The escorts are there to explain the mission, to take care of pesky details. They are also there to deliver bad news.

"It's a personal honor to be chosen," said Scott, who escorted families during a seamless, mid-1990s mission. "It means the crew trusts you. . . . They're putting their families in your hands."

Scott watched Saturday as the designated escorts whisked families of the Columbia astronauts to a private area. Everything appeared to go according to plan, he said, but still, "It's a tough duty."

Scott knew the crying wives and the ashen children on the television screen. Six of the crew members onboard had been part of the small community of astronauts in Houston where Scott was immersed before retiring in 1999, a community he feels he never really left.

He remembered his daughter baby-sitting the children of Columbia's commander, Rick D. Husband. He could see pilot William C. "Willie" McCool sliding through the lane for a layup at the base gym and trading tips about owning a private plane with mission specialist David M. Brown.

Mostly, though, he kept hearing mission specialist Kalpana Chawla's "gay, hearty laugh." Chawla had been the prankster when they went into space together in 1997, always concocting new games to entertain the crew. The best, he said, was called "pinwheel": each of the astronauts clasped a colleague's heels, then the whole floating group spun in unison.

Scott played the role of the seasoned veteran on that flight. But there had been so many before him, one replacing the next. Scott had been counseled by Story Musgrave, the man he calls "the grand guru of space flight . . . a scientist-artist."

In his early days as an astronaut, Scott wanted to talk details about some trouble he was having with a spacewalk. But Musgrave lifted the conversation to another level.

"He describes a spacewalk like a ballet -- 'Blend with the suit, don't fight the suit,' " Scott remembered being told.

The conversations often trailed out of conference rooms and into back yards. Their lives revolved around one another, Scott said. There wasn't room for much else. Their world tended toward all-inclusiveness.

There was an all-astronaut band, MAX Q, which exists today, as one group of space travelers leaves and is replaced by another. Husband was known to belt out a few rounds with the band in his slowly metered, back-country drawl, Scott said.

A night out probably meant dinner at another astronaut's house, he said, recalling an evening spent squinting up at the sky through the collection of telescopes arrayed in the back yard of Takao Doi, a Japanese astronaut involved in the space program's international partnership. Doi wowed them all by spotting the constellations, even the obscure ones, Scott said.

But it was seldom long, Scott said, before they were talking again about rockets and fuel and the thrill of looking down on Earth from above. They knew the dangers, but they didn't bother to talk about them much. Not even when they picked their family escorts.

When it came time for Henricks to pick his escort for the Columbia mission he commanded in 1996, he didn't have to think much about his choice. He picked a young guy named Rick Husband, who would go on to become a commander himself.

Researcher Madonna Lebling contributed to this report.

Above, astronaut Winston E. Scott, who went into space on Columbia in 1997, remembers mission specialist Kalpana Chawla's "gay, hearty laugh." Tom Henricks, right, recalls visiting the home of a fellow astronaut who was killed in the Challenger explosion in 1986. "It was emotional," he said.