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).
Pro Excellent construction sandbox for building and launching rockets
KSP at its core is a rocket building and launching sandbox. When creating a rocket you can place engines, fuel cells, structural elements, and even parachutes, allowing you to build a rocket in any shape and size. The end result can even look like a giant doughnut, which might be difficult to get it into outer space. Even if you fail, the entirety of the process is really enjoyable.