Martin Schweiger's "Orbiter" is a freeware space flight simulator for the PC that is fun, powerful, realistic, expandable, and educational. Based on the real science and math of orbital mechanics and atmospheric flight, it features a first-person astronaut's perspective and beautiful 3D graphics. Orbiter's developer, Dr. Martin Schweiger, has created an amazing virtual world of real and fictional spacecraft, space stations, planets, and moons. It includes a variety of spacecraft, space stations, and sample scenarios or missions.