The cute little Kerbals can die, but the goal is to get them into space (and hopefully back, but probably not). Kerbal Space Program is in early access and costs $29.99.
Pro Teaches orbital dynamics & rocket design fundamentals in an accessible manner
The physics engine does a reasonably accurate job of replicating the fundamentals behind both orbital dynamics and rocket design, so by going through the tutorials and experimenting, you're actually learning some real rocket science.
Pro You just can't get bored with it, and you will learn a lot
A "physics" game about space. Build rockets, space planes, space stations, rovers, landers, probes. Explore planets, moons, capture asteroids. With the addition of mods you can even test warp drive, set up a communications network, colonize a planet, mine for resources and much much more. It can even simulate our solar system (the in-game one is very similiar, although smaller to encourage new players.
Learn orbital mechanics. Inspire yourself to learn about space and space travel history of human. This game is not only fun - it is inspiring.
The game is under heavy development but is already playable (and gives a ton of fun!).
Works very well under Linux (64bit as well).