What are some alternatives?
When comparing Universe Sandbox and Kerbal Space Program, you can also consider the following products
Celestia - Celestia - real-time 3D visualization of space.
EVE Online - Player-created empires, player-driven markets, and endless ways to embark on your personal sci-fi adventure.
Stellarium - Stellarium is a free open source planetarium for your computer.
Star Citizen - 1, 966, 341. Active citizen. Help us make Star Citizen a reality! Become a backer of the next-generation of Space-man. Reserve your ship.
Space Engine - Space Engine is a realistic virtual Universe you can explore on your computer.
Star Conflict - Star Conflict is a free MMO action game and space simulator that was introduced in 2012.