Credit: NASA

As soon as they got to Jupiter, she'd get Ricky adopted. It would be a terrible wrench to give him up, but it wasn't fair to keep him. He needed a competent mother, not her. The decision made her feel better for a while, replacing shame and panic with simple grief.

How much longer would this go on? Presumably Ricky would sleep from exhaustion eventually.

Helen's Mum screamed, "Stop being such a baby! I can't stand it!"

But the baby screamed on, jerking his tiny legs to his belly.

It was so hard to think, between noise, exhaustion and self-doubt. If only she had some earplugs! Her emotions swung wildly. First she'd pity Ricky. Then she'd pity herself. Nobody could cope with this indefinitely.

If she squeezed his throat for a little while, then the noise would stop. She could sleep. Hours and hours of blissful, uninterrupted sleep.

Helen almost screamed herself. Had she really thought that? She covered the top of the baby's head with kisses, muttering, "I'm sorry. I'm sorry. Oh Ricky, sweetheart, I'm so sorry," as though he'd heard her murderous thoughts and understood them. Kisses couldn't drive away her guilt.

It swirled round her head along with her tears. She was a monster.

And if she strangled him it would be quiet.

My God, who was she?

Exhaustion.

Guilt.

This couldn't be real.

Mum yelled, "If you don't shut up, I'll put you out of the airlock!"

Ricky. The baby Mum was holding was called Ricky too. How odd.

Something snapped. Flesh and blood could only take so much. One handed, she flung towels out of a wall net. Then she gently put Ricky in the net and went into the airlock. She shut the door behind her, and the volume reduced considerably. Helen gave a long shuddering sigh. She could think - sort of. The crying still set her teeth on edge, but it didn't fill the universe any more.

What was that relaxation exercise they used to do at school? Helen shut her eyes, breathed in through her nose and out through her mouth. She pictured a tropical beach with waves gently lapping the silver sand. And a baby lying on the beach, screaming.

It was no good. She couldn't even manage a simple relaxation exercise. There was no way she could relax with that noise going on, even in the background. She took a spacesuit out of the rack and got in. Then she evacuated the airlock. She didn't need to open the outer doors; no air meant no sound.

Silence.

Beautiful, sumptuous silence. Helen stretched out in it like a cat.

It was wonderful.

Time to think.

In the memory - if it was a memory - Mum was huge. So if it was real, Helen would have been very young, about three. That would explain why she hadn't remembered any of it before. But it couldn't be a memory because she'd never had a brother. Unless the first Ricky died and they'd never told her.

She must have been mad to get pregnant. What on earth gave her the idea that she could be a better mother than her own mother had been? She'd wanted to murder a helpless child. Could she live with herself, knowing that?

She was a complete failure as a mother. She hated herself. And she didn't have to listen to that screaming any more.

She cried with exhaustion, guilt, and relief.

How long had she been out here? She'd better go see to that baby.

Helen refilled the airlock and got out of the suit. The crying had stopped.

She went back into the main living room, and found the silence unnerving. She dashed over to the wall net.

Ricky was asleep. He smelt of diaper.

She lifted him out and cradled him, drinking in the silence and the wonder of him. He pulled the strangest faces in his sleep. A sloping forehead like ET and a pointy crown to his head. Tiny clenched fists. Tiny arms that jerked out every few minutes, as though he dreamed of popping out into the big wide world.

She stroked the soft, fine, auburn curls. She marvelled anew at the umbilical stump, drying out already. Had she really thought of strangling the poor, helpless mite? A baby deserved a better mother than her. He had a little bruise on his nose from being born. She kissed it.

"Congratulations Helen," said the AI. "In spite of your childhood you passed the new parenthood exam with distinction. Unlimited breeding rights."

Ricky and the spaceship disappeared. She was back in the floatation tank. Wires slithered out of her scalp. It wasn't painful, but it was the tactile equivalent of chalk on blackboard.

The AI was still talking. "It took you seven hours to reach breaking point - most unusual - and even then you didn't have flashbacks or hurt the baby."

Flashbacks. Hurt the baby...

Mum towered over her, her face distorted into a Halloween mask. "Helen! WHAT HAVE YOU DONE WITH RICKY?"

Her mum screamed and screamed, just like Ricky.

The emotional earthquake shook great chunks of memory free that came crashing down on Helen like concrete blocks. She'd hated little Ricky. He'd taken her happy Mum and turned her into a tearful stranger. She'd longed for him to disappear.

And she'd murdered him. Shoved him out of the airlock like garbage. No wonder the doctors had insisted on full psychological testing. Dear God, how had the poor mite felt when the vacuum ripped the air from his lungs and he couldn't even scream any more?

She could hear screaming.

"Oh dear," said the AI. "You'd repressed it, hadn't you?"

Helen realised the screams ricocheting off the grey metal walls were her own, but she couldn't stop.