One of the inescapable perils of space is the rain of meteorites and manmade debris. Even a tiny fragment can be a devastating missile when it’s hurtling at thousands of miles per hour.

As they drew closer and the station filled the window, Emma felt such overwhelming awe and pride that tears suddenly flashed in her eyes.

Home, she thought. I’m coming home.

The air-lock hatch swung open, and a wide brown face grinned at them from the other end of the vestibule connecting Atlantis with ISS. “They brought oranges!” Luther Ames called out to his mates. “I can smell’em!”

“NASA home delivery service,” deadpanned Commander Vance.

“Your groceries have arrived.” Bearing a nylon sack of fresh fruit, Vance floated through Atlantis’s air lock into the space station.

It had been a perfect docking. With both spacecrafts traveling at a speed of 17,500 miles per hour above the earth, Vance had approached ISS at the delicate rate of two inches per second, up Atlantis’s docking module to the ISS port for a good, tight lock.

Now the hatches were open and Atlantis’s crew floated one by one into the space station to be greeted with handshakes and hugs, and the welcoming smiles of people who have not seen new faces in over a month.

The node was too small to hold thirteen people, and the crews quickly spilled into the adjoining modules.

Emma was the fifth to cross into the station. She popped out of the vestibule and inhaled a m?lange of scents, the slightly stale and meaty odors of humans confined too long in a closed space.

Luther Ames, an old friend from astronaut training, was the first to greet her.

“Dr. Watson, I presume!” he boomed out, pulling her into a hug.

“Welcome aboard. The more ladies, the merrier.”

“Hey, you know I’m no lady.” He winked. “We’ll keep that between us.” Luther had always been larger than life, a man whose good cheer could fill a room.

Every one liked Luther because Luther liked everyone. Emma was glad to have him aboard.

Especially when she turned to look at her other station mates.

She shook hands first with Michael Griggs, the ISS commander, and found his greeting polite but almost military. Diana Estes, an Englishwoman sent up by the European Space Agency, was not much warmer. She smiled, but her eyes were a strange glacial blue. Cool and distant.

Emma turned next to the Russian, Nicolai Rudenko, who had been aboard ISS the longest—almost five months. The module lights seemed to wash all the color from his face, turning it as gray as the gray-flecked stubble of his beard. As they shook hands, his gaze barely met hers. This man, she thought, needs to go home. He is depressed. Exhausted. Kenichi Hirai, the astronaut from NASDA, floated forward to greet her next. He, at least, had a smile on his face and a firm handshake. He stammered a greeting and quickly retreated.

By now the module had emptied out, the rest of the group dispersing to other parts of the station. She found herself alone with Bill Haning.

Debbie Haning had died three days ago. Atlantis would be bringing Bill home, not to his wife’s bedside, but to her funeral.

Emma floated across to him. “I’m sorry,” she said softly. “I’m sorry.” He merely nodded and looked away. “It’s strange,” he said. “We always thought—if something ever happened—it would happen to me. Because I’m the big hero in the family. The one who takes all the risks. It never occurred to us that she would be the one.”

He took a deep breath. She saw that he was fighting to maintain his composure, and she knew this was not the time for words of sympathy.

Even a gentle touch might destroy his fragile control over his emotions.

“Well, Watson,” he finally said. “I guess I should be the one to show you the ropes. Since you’ll be taking on my load.”

She nodded. “Whenever you’re ready, Bill.”

“Let’s do it now. There’s a lot to tell you. And not much time the changeover.” Though Emma was familiar with the layout of the station, her first interior glimpse of the actual structure was a dizzying experience. The weightlessness of orbit meant there was no up or down, no floor or ceiling. Every surface was functional workspace, and she turned too quickly in midair, she instantly lost all sense of direction.

That, and the twinges of nausea, made her move slowly, focusing her eyes on one spot as she turned.

She knew that the core of ISS had as much inhabitable airspace as two Boeing 747s, but it was distributed among a dozen bus-sized modules, plugged together like Tinkertoys into connecting points called nodes.

The shuttle had docked on Node 2. Attached to that same node were the European Space Agency lab, the Japanese lab, and the U.S. Lab, which served as the gateway into the sections of the station.

Bill led her out of the U.S. Lab into the next connecting point, Node 1. Here they paused for a moment to look out the observation cupola. The earth slowly spun beneath them, milky clouds swirling over seas.

“This is where I spend every spare moment,” said Bill. “Just looking out these windows. It feels almost sacred to me. I call it the Church of Mother Earth.” He tore his gaze away from the view and turned to point out the other node hatchways. “Directly opposite is the EVA air lock,” he said.

“And the hatchway below into the hab module. Your sleep station’s in there. The CRV is docked at the other end of the hab, for quick evac access.”

“Three crew members sleep in this hab?”

He nodded. “The other three sleep in the Russian service module. It’s through this hatchway here. Let’s head there now.” They left Node 1, and like fish swimming through a maze of tunnels, they floated into the Russian half of the station.

This was the oldest part of ISS, the section that had been in orbit longest, and its age showed. As they passed through Zarya—the power and propulsion plant—she saw smudges on the walls, the occasional scratch and dent. What had been only a set of blueprints in her head now took on texture and sensory detail. The station was more than just a maze of gleaming labs, it was also a habitat for human beings, and the wear and tear of constant occupancy was evident.

They floated into the Russian service module, and Emma was confronted with a disorienting view of Griggs and Vance, both of them upside down. Or am I the one who’s upside down? thought Emma, amused by this topsyturvy world of weightlessness. Like the U.S. hab, the RSM contained a galley, toilet, and sleep stations for crew members. At the far end, she spotted another hatchway.

“Does that go to the old Soyuz?” she asked.

Bill nodded. “We use it for storing junk now. That’s about all we can do with it.” The Soyuz capsule, which had once served as emergency lifeboat, was now obsolete, and its batteries had long since drained.

Luther Ames popped his head into the RSM. “Hey, everyone, it’s show time! Group hug in the media conferencing center. NASA wants the taxpayers to see our international love fest up here.” Bill gave a weary sigh. “We’re like animals in a zoo. Every day it’s smile for the damn cameras.” Emma was the last to join the exodus to the hab module. By the time she reached it, a dozen people were already crowded inside. It looked like a tangle of arms and legs in there, everyone bobbing, trying not to collide with each other.

While Griggs struggled to get things organized, Emma hung back in Node 1. Drifting in midair, she found herself slowly moving toward the cupola. The view beyond those windows took her breath away.

The earth stretched below in all its magnificence, a rim of stars crowning the gentle curve of the horizon. They were passing into night now, and below, she saw familiar landmarks slipping into darkness.

Houston. It was their first passover of the night.

She leaned close to the window, pressing her hand to the glass.