An updated version of the free spaceflight sim Orbiter is now available: Orbiter 2016 Space Flight Simulator
Explore the solar system on your PC! 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. And best of all: you can download it for free!
Here is a positive review of the update: Orbiter 2016 and other space flight simulators – Bruce Irving/The Space Review
Although it is fun and challenging in many ways, Orbiter 2016 truly is a space flight simulation, or what some might now call a “sandbox game.” In its level of detail and learning curve, it is something like Microsoft Flight Simulator or X-Plane, where the “game” is mainly the challenge of learning to fly, or of mastering advanced skills such as instrument approaches. Orbiter too supports atmospheric flight, but with the major addition of space flight with accurate orbital mechanics.
There is plenty to learn and do, but there are no requirements, characters, weapons, or scores, only the unforgiving rules of Newtonian physics, a wide range of tools and techniques to master, and the full solar system to explore. Learning to launch a spacecraft to orbit, dock with the ISS, land on the Moon, or navigate to Mars: all of this, and more, is possible in Orbiter.
You can choose from a variety of built-in spacecraft and scenarios, download and fly add-on spacecraft and scenarios, or even design and fly your own spacecraft, although doing so requires some external tools.
Irving also has good things to say about these two spaceflight sims: