Orbiter is a freeware space flight simulator created by Martin Schweiger, Ph. D., of the Department of Medical Physics and Bioengineering at University College London. The most current stable version is Orbiter 2010.
Orbiter is a physics simulator which uses Newtonian physics to simulate the behaviour of spacecraft & other objects within our solar system. While somewhat vulnerable to crashes caused by addons or extreme simulation demands, Orbiter is generally quite stable when used properly. Orbiters filestructure consists of configuration files, help files, meshes, textures and modules which are integrated by the main executable Orbiter.exe. This very flexible architecture makes addon development for Orbiter relatively easy.
 System Requirements
The standard ORBITER distribution requires the following minimum hardware features:
- 600 MHz PC or better (Pentium, Athlon, etc.)
- 256 MB RAM or more
- Windows 9x/Me/2000/XP
- DirectX 7.0 or higher
- DirectX compatible 3D graphics accelerator card with at least 16MB of video RAM (32MB or more recommended) and DXT texture compression support
- Approximately 100MB of free disk space for the minimum installation (additional high resolution textures and addons will require more space).
- DirectX compatible joystick (optional)
Installing high-resolution texture packs or addons may have an impact on performance and could require significantly higher computing specs.
 The default solar system
The default solar system includes all known planets (except the dwarf planets) and the major moons. Most planets are equipped with a ephemeris module, which calculate the position of the celestial bodies to a very high accuracy, making it possible to simulate historic space missions by using nearly the same maneuvers as in reality.
Also included in the basic Orbiter distribution are several spaceports, where players can refuel their spacecraft:
- Kennedy Space Center
- Habana located close to Habana, Cuba
- Brighton Beach located on the Moon near side
- Olympus spaceport located on Mars
For a complete list of the bases included with the Orbiter distribution, see the Surface bases article.
 Standard Spacecraft
- Luna Wheel Station
- Space Shuttle Atlantis
- Shuttle PB
- Hubble Space Telescope
- Long Duration Exposition Facility
- International Space Station
In spite of its destruction in reality, Mir is placed in an alternative orbit making it a possible start for interplanetary missions.