Mare didn't get forever. She had barely two more years before she failed a physical.

She didn't cry when they told her she had to go down again, had to stay down. She didn't cry when they told her it was a genetic affliction, that they couldn't fix her the way they could fix everyone else, that she might never get her bone density back to what it should be, that she might be hunched over like a grandmother for the rest of her life. She didn't cry when they showed her medical charts, graphs, gene maps, X rays. She didn't cry when they told her she'd have to spend the first year in a wheelchair, when they told her she might never walk properly.

She cried on reentry.

A week after the letter came, they drove up into the mountains to watch the station travel over them. Mare had planned their trip so they could stop at a rest area up beyond the lights of the city. Jack spread the blanket over the damp grass in the pale, cold predawn light, and they stretched out on it and watched the stars, so much brighter than in the city, while they waited.

"I'll be closer to you at night," she said, head resting in his lap as she watched the sky.

"Really?"

"No. But you'll be able to see me at night." Mare pointed suddenly. "Look! Way up, right there."

Jack followed the line of her finger up, trying to see what she was pointing at. "I don't see it. There are too many stars to find anything."

She pushed herself halfway up from the blanket with her free hand and grabbed his wrist in her other hand, positioning it so she could sight along it. "There," she said finally. "Below the moon, the blinking light. That's where I will be." She sank back down to his lap again, watching the station drift across the sky.

He watched it for a moment, his face smooth and expressionless in the dim light, before dropping his eyes to her again. His jaw was tight. "You're sure this is what you want to do?"

She didn't answer, just watched in silence until the blinking light moved out of sight across the sky. "That was it. We can go now." She made no effort to get up.

"Are you sure this is the best thing to do?" he asked again, brushing her hair back from her face.

She closed her eyes and felt him continue to run his fingers through her hair. "No. But I need to do it. I'll never get this sort of opportunity again." His fingers slowed against her temple and then started again. "It's only a few years."

"We could stay together." His voice dropped to nearly a whisper, and she had to strain to hear him. His hand had stilled again, cupping the side of her face. She rolled over and off his lap, pressing a kiss into his palm as she moved.

"I can't do that to you." She rose to her feet without stumbling in the wet grass, and offered her hand to him when he made no move to follow.

She liked remembering Jack best from that night—the line of his face as she'd looked up at him, the curve of his body reaching up for her hand.

Even after he stood up, he didn't let go of her hand until she pulled away from him. "We could just be friends."

Her heart skipped uncomfortably when she saw it in the mailbox, her throat tightened, her eyes felt hot. Flimsy foreign airmail envelope stretched taut over the stack of whisper-thin onionskin inside—so little to make so much of a difference. The pages, slick and delicate, drifted through her fingers when she opened the envelope and spilled across the table in front of her. Contracts, proposals, waivers. Lists of experiments planned and already completed. Mare sorted the papers as she read them. "Scary." "Standard." "Exciting." She moved the invitation from one pile to the next, unable to settle for just one emotion.

The next day she found an old legal pad and cleared everything off the kitchen table so she'd have space to work. She drew a line down the center of the tablet and labeled the two columns. The pro side of the list rapidly outgrew the space she had for it, but she could have summed it all up in just one word if she'd had to: Space. The con side grew more slowly, but with more thought. Unfamiliar country. Unfamiliar language. Isolation. Loneliness. Little job security.

She wasn't sure why she bothered with the cons. The pros would win. They'd won the first moment she'd heard the voice on the other end of the phone line, such a thick accent that she'd had to ask them to repeat themselves three times. Well, twice because of the accent. The third time just to revel in the words. International exchange program. Diversity opening on the space station. She'd barely been able to form the words they'd wanted to hear. And no sooner had she finished saying them than she second-guessed herself, biting her lip so hard she nearly cried out. She couldn't just pick up and leave. This wasn't summer camp.

The contract was for four years—one year in China, one year on the space station, and then repeat. At the end of that term, maybe they'd re-up, maybe she'd come home again. She wouldn't know until the end of the third year, if then, and that fact alone made her nervous. But still, at the very least, that was two years on the station, two years in space. She could spend her whole career, her whole life in NASA and not see a fraction of that time on the station. If she ever flew for NASA, they would let her keep her life the way it was—settled, structured, arranged around her priorities. If she went to China, she'd have to leave it all behind, lose her seniority when she came back, start over again from the bottom rung. But from her current rung, she couldn't see the top of the ladder, didn't even know if it really was up there, and now China was offering to show her the elevator.

She'd had all the training that NASA required. She just hadn't thought she'd ever really need it. She was so far down the list, she'd never make it on a flight without some sort of catastrophic accident, and after the last one they hadn't made it back into space for years. But maybe that's why China wanted her—she'd had enough of a taste to want more, enough experience to show she was serious, and only gravity to hold her down. Gravity, and Jack.

She knew all the risks involved. She just thought that it would be worth giving up everything for even one trip. To be up there, looking up, falling down, nothing but distance all around.

Years before, when she was still in school, her teachers, the older astronauts, the ones who had gone up, warned the class about vertigo, reminded her that weightlessness would make her inner ear think she was falling even when she held still. The Chinese instructors her first year talked about it too, telling the students that some of them would have to come home in the first month, that some others would be able to control it with drugs, but that it was not something to worry about until it was an issue. Despite what they said, or maybe because of it, she'd thought about it a lot the first year, usually late at night when she couldn't sleep for worrying. She got dizzy when trains passed her standing still, when the car next to her moved first at a green light. She pictured months of nausea or drug-induced calm. When she did sleep those nights, she dreamt of falling, of waiting to hit. Sometimes you learn to fly, she thought in the dream once, but she never did. She just fell, like Mickey in the night kitchen, like Alice down the rabbit hole, endlessly on.

She and Jack were still together, sort of, the first time she went up. At least, she hadn't tried to break up with him again. Before she left for China, she set up his screen saver to track the progress of the station across the sky, so once she was up there, he'd know when to wave. He swore he did, every time he could, and so she waved, if she was awake, and not busy, and remembered where they were. The onboard camera caught her waving one night, and she made the "fun" picture in newspapers across the country the next morning. He sent her a copy of the photo and for years afterwards she would look at the black and white photo, herself flattened into harsh separations, and try to remember if she'd missed him at that moment.

That first year up, he'd still called frequently, or at least what passed for frequently on the station. Once a month her turn came up in the rotation and she'd spend a half hour in a small room at a phone that flickered and lagged.

"I miss you," he'd always say, and she'd parrot him, even though she didn't, even though she was too busy, too excited, too thrilled to even think of him other than late at night when she couldn't sleep. He'd tell her all the news, and she'd nod and smile, and hope she looked like she was interested. She'd tell him her news, and watch him nod and smile and wonder if he really was interested or just better at acting than she was.

Her face would start to ache a little even before the phone call ended, from the newly-unfamiliar shapes her mouth had to make, and English would echo oddly in her head. Some times her attention would lag as she tried to translate, not remembering that it already was English. She'd no sooner get accustomed to it than the call would end, and she'd find herself absently answering questions in English for the rest of the day. She could tell when the other English speakers had their turns in the rotation as well, for they'd seek her out at mealtime, small clusters of Anglophones, so the sudden lapses into English mid-sentence wouldn't be commented on, or possibly even noticed.

No relationship could survive on just six hours of communication in a year, and so he'd written much more often, the messages loading up and down twice a day when the station connected. He sent her photos almost every day, but always ones the space station had taken. Her favorites were the night photos of the cities, urban sprawls creating sequined appliqués, highways like a sprinkling of Christmas lights across the land, the great dark patches that interrupted everything. Seventy percent of the Earth's surface is covered in water, she reminded herself, tracing the spills of lights that stopped abruptly or wiggled around dark shapes.

Some photos he annotated for her. "Wish you were here," he wrote on a pale blank photo of a snow-covered Michigan the week of their tenth college reunion. Everyone she'd known had sent a note in that batch, most of them complaining about the weather. She dreamt of snowstorms that night, and the shards of ice that blew out of the airlocks when they vented, snowflakes sharp enough to slice flesh, like the winds off the lake at school.

She was dizzy the first week up, which she had expected, and every time they came down, which she hadn't. She noticed that first thing when they touched down, realized right away that she no longer fell. It was like vertigo all over again, but worse. Now she felt like she was standing still, like nothing moved, nothing happened. Before she came down, she'd promised to use her vacation time to visit Jack right away, and he held her to it. Once she landed, Mare knew she shouldn't have, should have waited to visit him at least until she'd adjusted to being heavy again, possibly forever, but he hadn't wanted to wait, he expected her to pick up where she'd left, to step back into the life she'd left behind. She felt like a relativistic twin, but which one? Had life gone on without her, or had she gone on without life?

Maybe if she'd been on the Moon instead, she wouldn't have noticed so much, but every time she moved she hurt more than she'd remembered, more than she thought possible. She knew she could feel bones grinding against each other when she moved, and even though it was psychosomatic, she couldn't make the pain leave.

Jack fussed and worried over her, but all she wanted was to have some time alone to remember how to live with gravity. She had forgotten how heavy life was, how hard she had to push against the world for the simplest things—air in her lungs, blood through her veins. The sun was different, the air was different, even food tasted different.

"Don't worry. We'll clean it up together," he'd say, like she was a child, when she'd forget the laws of gravity and drop things—books, silverware, a dozen eggs. "I'm here for you," he'd say, and she'd have to choke down her urge to tell him to go away.

She spent as much time as she could in the pool for the first few weeks after she'd come down, but it wasn't the same. Similar, but even when she tried to pretend, she could still feel the water holding her up. "Go away," she'd tell it, but it wouldn't listen any more than Jack did.

Orbiting is just a fancy name for falling and missing. She'd taken physics for years, but that was the one piece she consciously remembered, the one that she took out and looked at from time to time. Falling. She fell towards the Earth, and the Earth fell towards the sun, and the sun in turn fell towards the galaxy, and so on and so forth. It wasn't strictly accurate, she knew, but that was how she always thought of it. Like a trust fall, but she trusted instead that the Earth wouldn't sweep up below her feet, that she'd keep falling forever, like Newton's apple.

They called Mare at the end of her third year, just before she was due to report for her preflight physical, just after a phone call from Jack. She'd been hoping just for a renewal, two or three or even four more years up. Instead they offered her forever.

She told them she'd call back with her decision. There was a fifth of imported vodka in her pack, a present for the ex-Russian pilot who'd be running the station when she got up there. She cracked the seal with a fingernail, and drank directly from the bottle. She pulled their college pre-engagement picture out of the bag of personal items she had packed to take up and set it up on the desk so he could participate in the discussion the way she wanted, without arguing. His eyes said "Come home," and she knew he was serious this time. She hadn't asked him to wait, but he had so far. She knew he couldn't wait any longer.

Vodka gave her a stomachache, but she didn't notice it when she was buzzed. She drank slowly, or thought quickly, but she still had a little more than half a bottle left when she made up her mind. She flipped the picture face down on the desk and reached for the phone. "Hello? Hello?" She practiced a few times before they picked up, just to make sure she wasn't slurring the words.

She'd always known he'd fallen for her, but she couldn't believe he thought it should change her mind, change her life. "Marriage is about compromise," he'd say, but she couldn't tell what he would give up that would balance her sacrifice. When they spoke after that, stilted and uneasy, she could feel the ground rush up to meet her, feel him pulling her down. He'd always called himself her safety net. "I'll be here when you need me," he said, and she wondered why he still hadn't realized that she didn't need to be caught, that she didn't want to land.

Worse than saying the words, it hurt to hang up on him, hurt even more to watch him hang up on her, even when she knew it was for the best. It was better when he stopped calling her, when she cleaned his emails from her inbox, sent the box of things that reminded her of him back down to Earth.

When people said, "you'll get over it," she hadn't thought they meant one day she'd wake up and the empty hollow in her heart would have filled itself in overnight. But one day she looked at a night shot of London, and her heart didn't stutter, and her throat didn't hurt. The space where the hollow had been still ached some days, such as when he sent pictures of the wedding that could have been hers, but she was still happy at the end of the day. She was still falling.

She cried during reentry, when she felt the weight of the world pulling her down into the chair again. She cried when she realized that she'd never again feel the bearlike weight on her chest as they took off, the tingle in her fingers and toes once the g-forces were over. She cried when she realized the closest she'd ever get to weightless again would be that split second in the water, after she dove in, after she went down, before she came up. She cried when she felt tears rolling down her cheeks.