Ender's Game - Orson Scott Card
The alien race is set to invade again and it is the children like Ender who must learn how to win the game.
A brilliant young boy, Andrew "Ender" Wiggin lives with his kind but distant parents, his sadistic brother Peter, and the person he loves more than anyone else, his sister Valentine. He is drafted to the orbiting Battle School for rigorous military training and to learn to win.
Insignia - S.J. Kincaid
The planet's natural resources are almost gone, and WWIII is being fought to control the assets of the solar system. The enemy is winning. The salvation may be Tom Raines. Tom doesn't seem like a hero. He's a short fourteen-year-old with bad skin. But he has the virtual-reality gaming skills that make him a phenomenon behind the controls of the battle drones. (Goodreads)
Trading In Danger - Elizabeth Moon
Ky Vatta is a highly promising military cadet with a great future ahead of her, until an apparently insignificant act of kindness maker her the focus of the Academy's wrath. She is forced to resign, but then to her surprise, Ky is offered the captaincy of a ship headed for scrap with its final cargo. Her orders are absolutely clear, but it's in her blood to trade - even if the currency is extreme danger.
The Martian - Andy Weir
Six astronauts have arrived on Mars for a 30 sol mission. On sol 6 a storm threatens their survival and as they make their way to the escape vessel Mark is swept away. The crew can't find him but can see his vital signs are zero so they blast off, leaving him on Mars. But he isn't dead. Described as 'Robinson Crusoe meets Gravity', this is a brilliant read with plenty of science thrown in.
2001 A Space Odyssey: Arthur C. Clarke
One of the most famous sci-fi novels. A revolutionary book of it's time and still a great story.
I Am Number Four - Pittacus Lore #1
In rural Ohio, friendships and a beautiful girl prove distracting to a fifteen-year-old who has hidden on Earth for ten years waiting to develop the Legacies, or powers, he will need to rejoin the other six surviving Garde members and fight the Mogadorians who destroyed their planet, Lorien.
Wool - Hugh Howey
Deep in an underground silo live an entire community ranging from the energy team in the base to the sherrif at the top. With only one window onto their ruined planet this community relies on the convicted offenders going outside with wool to clean the window. They never come back.
Daniel X: Alien Hunter - James Patterson #1
Long ago, after his parents were murdered, Daniel X inherited the 'List of Alien Outlaws' and took over his father's job as Alien Hunter. Number 7 on the list is the insectile grandmaster of an interplanetary game of destruction that could result in the eventual take over of Earth.When #7 reveals his true and terrifying powers, Daniel must enlist the help of #7's own son, Kildare, to bring the evil alien to justice.
The Colour Of Magic - Terry Pratchett
The first book of the fantastic Discworld series. No sci-fi collection would be complete without the hilarious world that Pratchett created.