The best Flight Simulator alternative to Kerbal Space Program is Orbiter, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to Kerbal Space Program and five of them are Flight Simulators so hopefully you can find a suitable replacement. Other interesting Flight Simulator alternatives to Kerbal Space Program are Juno: New Origins, Reentry, Kitten Space Agency and Rocket Science.
Orbiter is a realistic 3D real-time space flight simulator program.
Fed up with space games that insult your intelligence and violate every law of physics? Orbiter is a simulator that gives you an idea what space flight really feels like - today and in the not so distant future.
Bring to life anything you can imagine from rockets and airplanes to cars and more. Automate them with a visual programming language. Explore 3D planets and download more from the community. Share your creations online.
Reentry is a space flight simulator based on real life spacecrafts. You create a new astronaut, gain levels and experience for every move you make by completing missions in space.
Built from the ground up with the spirit of discovery, Kitten Space Agency invites players and supporters to join a community pushing the boundaries of what a spaceflight program can be.
Take part in a space program. Design spacecrafts and send them off to explore the vast expanses of space. Experience the real scale of the Solar system and the size of its celestial bodies.
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In no way is orbiter a KSP clone... it's a realistic simulator in continuous development for 21 years and counting. Orbiter is a flight simulator, not a game. When KSP just doesn't satisfy you anymore and you can calculate Hohmann transfers in your head, try this.