Frequently asked questions

A. General

B. Troubleshooting

C. Running Orbiter

A. General

A1. What is Orbiter?

Orbiter is a real-time 3D space flight simulator for the Windows PC. The concept is similar to traditional flight simulator software, but you are not limited to atmospheric flight. Orbiter allows you to experience manned and unmanned space flight missions from the pilot's perspective. Take control from launch to orbtial insertion, rendezvous with space stations, deploy and recapture satellites, and re-enter and land on a planetary surface. The playground is our solar system, and you can even execute missions to the moon or other planets. (Time compression is available to shorten long cruise phases.) Orbiter accurately models the physics of spaceflight, which makes it possible to either recreate historic missions, or use it as a sandbox for futuristic spacecraft concepts.

For more details on Orbiter, have a look at the mission statement, or the Orbiter Wikipedia entry.

A2. Is Orbiter really free?

The full Orbiter software can be downloaded from this site and is free for personal and non-commercial use. For details, see the Orbiter Freeware License terms. You can distribute Orbiter, but you are not allowed to charge a fee for it. If you paid for Orbiter (either on its own or as part of a compilation), you have probably been ripped off.

If you like Orbiter, you can show your appreciation by making a donation, but this is entirely voluntary.

If you want to use Orbiter in a context not covered by the freeware license terms, you must get written permission from the author.

Note that 3rd party Orbiter addons may be distributed under different licensing terms.

A3. Where can I post my suggestions/questions/corrections/bug reports?

There is a web-based Orbiter message board where you can post general questions and suggestions. It has dedicated sections for bug reports, addon topics, and all things spaceflight.

Additional forum sites and orbiter-related pages can be found under the Links page. Another useful link for tutorials and developer resources is the OrbiterSimulator Wiki. For general information on Orbiter, see the Orbiter Wikipedia entry.

Before submitting a bug report make sure you have the latest version, and that the problem is not already addressed in this FAQ or the forum.

As a last resort, you can email me directly, but I cannot guarantee that I will be able to answer all Orbiter posts.

A4. When will the next version be released, and what is going to be in it?

I don't announce release dates and feature lists. This is mainly because Orbiter is a hobby of mine, and I don't need the pressure of working against a deadline or fixed specification. I can't always predict how much time I can spend on Orbiter, so the interval between releases will vary. The features added in a new version are usually a mixture of my own ideas and user requests.

Occasionally screen shots of the upcoming version will be posted on the Gallery page, just to keep the suspense up.

A5. I have problems downloading Orbiter

Remember you need only the "Base" package to run Orbiter. Everything else is optional. Select a download mirror close to your location, and if necessary, try several (try to avoid the medphys server, because excessive demand on that server will get me into trouble ;)

If you have a slow connection, you may try at a different time of day when net traffic is lower. A download manager may help as well. Please note that I am not able to provide a CD distribution service, although Orbiter occasionally features on magazine cover discs (so this may be your last option).

A6. How can I write my own addons?

Addons are written in C++, so you need to know (or learn) a few basic programming skills, and have access to a C++ compiler (you can download a free one from Microsoft).

If you want to create your own addons, you need to familiarize yourself with the Orbiter Software Development Kit (SDK), found in the Orbitersdk directory of the Orbiter installation folder. It contains the libraries and header files to link your addon into the Orbiter core application.

The SDK also contains code samples (in Orbitersdk\samples) and documentation (in Orbitersdk\doc), in particular the API Reference Guide.

The Orbiter-Forum contains dedicated sections for SDK questions. If you get stuck, you may want to ask for help there (or propose a collaborative project). The Orbiter Wiki also has some resources for addon developers.

B. Troubleshooting

B1. I have downloaded Orbiter, but how do I install it?

The Orbiter installation package comes in two flavours: an MSI installation file for automatic installation, or a ZIP archive for manual installation.

If you get the MSI file, just run it. It will guide you through the installation process, and install Orbiter like a standard Windows application.

If you get the ZIP file, you need to unpack it yourself into a fresh directory. You cannot run Orbiter directly from within the ZIP archive. Note that you shouldn't place your Orbiter installation inside the Program Files folder, because newer Windows versions are a bit picky about this folder's contents. Use C:\Orbiter2016 or %HomePath%\Orbiter2016 or something similar.

The MSI installation is a bit simpler, and provides a desktop icon and Uninstall options, while the ZIP installation requires more manual intervention, but allows multiple installs and is less intrusive on the system. It is self-contained and doesn't modify system libraries and the Windows registry. To uninstall a ZIP installation, simply delete the Orbiter directory with all its contents.

Once you have installed Orbiter from either the MSI or ZIP file, locate the orbiter.exe file inside the Orbiter folder and run it.

B2. A previous installation worked fine, but the latest version causes problems.

Sometimes this problem occurs if a new version is installed over an old one. It is strongly recommended to always install new versions from scratch into a new directory rather than overwriting an existing installation. Installing from scratch can also solve problems caused by addons which are no longer compatible with a new version. If you suspect a problem may be caused by an addon, re-install your addons one at a time and see whether you can identify the culprit. If you can, you may consider notifying the author of the addon.

Multiple Orbiter installations can co-exist on the same computer, so it is a good idea to keep your old Orbiter version to fall back on, in case you can't get the latest version to work on your system.

B3. After installation, I don't see any scenarios listed, or I don't get any textures.

This problem usually occurs if the ZIP file is extracted into a flat directory, rather than preserving the directory structure of the archive. When using WinZip or a similar utility to unpack the Orbiter packages, you need to activate the "Use folder names" option (or an equivalent option to that effect). After installation, your Orbiter root directory should contain (amongst other things): the orbiter executable (Orbiter.exe), and a number of subdirectories, including Meshes, Scenarios, Textures. If all files ended up in a single directory, you made a mistake when unpacking.

B4. Orbiter takes a long time to load

Orbiter loads a large number of texture maps (mainly planetary surfaces) during startup. Loading these maps will be very slow if your graphics card does not support texture compression, because textures must then be decompressed on the fly. To reduce the loading time (and the amount of memory required for textures):

Disable high-resolution textures if you have any. High-resolution textures are located in the Textures2 subdirectory. The easiest way to disable them is to rename the directory. Orbiter will then use the lower-resolution textures in the Textures directory.

subdirectory. The easiest way to disable them is to rename the directory. Orbiter will then use the lower-resolution textures in the directory. Turn off visual effects in the "Visual effects" tab of the Orbiter Launchpad dialog. In particular the Cloud layers and Specular water reflections options are texture-intensive.

B5. I get a low frame rate

Make sure you have selected a hardware render device in the "Video" tab of the Orbiter Launchpad dialog (for example "Direct3D HAL T&L"). Avoid the much slower software devices, such as "RGB Emulation". If possible, use a hardware transform and lighting (T&L) device.

Apart from that, all the usual advice for performance-critical simulations applies: Quit other programs running simultaneously (either in the foreground, or as background jobs). On computers with low-end graphics run Orbiter in fullscreen mode, use a lower screen resolution and lower colour depth (16 bit).

Reduce the level of "eye-candy" by turning off the options under the "Visual effects" tab of the Orbiter Launchpad.

Try a different graphics engine: instead of running orbiter.exe with its built-in DX7 graphics engine, use orbiter_ng.exe and connect an external graphics client, such as the D3D9 client.

B6. Orbiter fails to run or crashes

Make sure your system meets the requirements specified in the Download page.

Make sure that you have installed Orbiter correctly.

Make sure that you have configured Orbiter correctly - in particular that the options under the "Video" tab of the Orbiter Launchpad are properly set.

The Orbiter.log file might contain information about what is going wrong.

B7. My joystick is not responding

Make sure you have enabled the joystick in the "Joystick" tab of the Orbiter Launchpad dialog. The joystick is usually mapped to the reaction control system (RCS) or aerodynamic control surfaces of your spacecraft, so remember:

In vacuum, aerodynamic control surfaces obviously have no effect - the spacecraft orientation can only be controlled with the RCS.

Conversely, in a dense atmosphere, the RCS may be too weak for attitude control. Control surfaces will be more effective.

When both RCS and control surfaces are disabled, the joystick has no effect.

In linear RCS mode, the joystick will not rotate the spacecraft, but add to the linear velocity vector.

If your joystick has a throttle control, you can use it to manipulate the main engines. If your throttle control is not responding, try selecting a different throttle axis from the Launchpad dialog.

B8. No sound!

The basic Orbiter installation doesn't include support for sound, but this can be added with the XRSound sound module by Douglas Beachy. XRSound requires Orbiter 2016 and later, but users of earlier Orbiter versions can use DanSteph's OrbiterSound plugin. If you want to use addon vessels that require OrbiterSound in Orbiter 2016, you can use the OrbiterSound → XRSound bridge contributed by Face.

B9. I don't see any stars

Orbiter renders stars (except for our sun, of course) as single pixels of varying intensity. This makes them quite faint (in particular at high screen resolutions), but also fairly realistic.

If your Orbiter definitely doesn't show any trace of stars, first check for the obvious: make sure that the star count, brightness and contrast levels under the "Parameters" tab of the Orbiter Launchpad are set correctly. If this doesn't help, and in particular if you also don't see any grid and constellation lines in "Planetarium" mode, then the most likely problem is the anti-aliasing setting of your graphics card. Try to open the configuration tool of your graphics driver, and disable anti-aliasing.

For a more colourful celestial background, you can also activate the "Background" option in the "Celestial sphere" section of the Visual effects tab.

B10. Orbit deteriorates at high time acceleration

Orbiter uses numerical integration methods for propagating spacecraft states from one simulation frame to the next. The accuracy of this method depends on the simulation time interval between frames. While Orbiter's numerical implementation is quite sophisticated (including high-order Runge-Kutta and symplectic integrators, and subsampling of time steps), it may still lead to problems when extreme time accelerations are used during high-acceleration phases of a spacecraft (e.g. in low orbit).

It is generally a good idea to avoid high time accelerations when in low orbit, and in particular during powered flight. Orbiter also provides an "orbit stabilisation" mechanism that disables the numerical state integration in critical phases. Orbit stabilisation can be configured in the "Extra" tab of the Orbiter Launchpad.

B11. Orbiter dies unexpectedly during startup ...

... and the Orbiter.log file shows something like

ERROR: DDraw object is still referenced: 50

ERROR: Destroy framework objects failed

This orbiter log message is a generic indicator that something went wrong and orbiter tried a shutdown during which it couldn't remove all its previously created graphics objects.

This could be caused by any number of problems, for example by low system memory, by a graphics driver problem, another process running in the background, a misbehaving addon, or by a bug in the Orbiter core.

Try running a fresh orbiter installation (without any addons), use a low-resolution video resolution (say 800x600), try different video devices, turn off all the options in the "Visual parameters" tab, and don't use any high-resolution textures.

If nothing helps, your last option may be posting a message on the forum with as much information about your system (hardware, OS, graphics drivers, DirectX version etc.) as possible. With any luck, somebody with a similar system may have a solution.

Running Orbiter

C1. I've installed Orbiter, how do I start?

Assuming you have configured the video and other options in the Orbiter Launchpad dialog, you are ready to take off. Pick a scenario from the list, and click the "ORBITER" button.

In a nutshell, the most important controls are on the numerical pad of your keyboard: Ctrl+ for increasing main thrust, Ctrl- for decreasing main thrust or engaging retros, Ins and Del for increasing/decreasing hovers (if available), and cursor keys for attitude controls. You should read the Orbiter manual in the Doc folder for a full list of keyboard functions, as well as explanations of the instrumentation.

C2. Why can't I get into orbit?

To reach orbit from a planetary surface, you need to do two things: attain sufficient altitude, and sufficient tangential velocity. The first point is easy, but unless you reach sufficient tangential velocity, you will simply fall back to Earth again in a ballistic trajectory. The required velocity depends on the orbit altitude and planet mass. For example, a low Earth orbit (LEO) requires a velocity of more than 7000 metres/second.

Orbital launchers usually take off vertically to clear the dense part of the atmosphere quickly, before pitching down to add to the tangential velocity component. You should always launch into a prograde orbit (towards east) to utilise the planet rotation. Orbit insertion normally occurs in two stages: the initial burn leads to a ballistic trajectory, and a second (orbit insertion) burn at the highest point of the trajectory (apoapsis) to raise the periapsis (lowest point of the orbit).

If you are new to Orbiter, you should try your first orbit insertions with one of the more powerful spacecraft, like the Delta-glider. The more realistic launchers, like the Space Shuttle, don't provide much margin for error. If you feel ready to take on the Shuttle, make sure you turn on the "limited fuel" option. With unlimited fuel, the Shuttle is too heavy to reach orbit!

C3. I want to rendezvous with the ISS, but I can't even get close

The first step for a successful rendezvous manoeuvre takes place before launch. You should launch into an orbit with as little inclination to the orbital plane of the target as possible. This means waiting until the orbital plane of the target passes through your launch site (use the Map MFD to monitor this). By launching at the right time and into the right direction, you can minimise the need for later corrections of the orbital plane (once in orbit, you can use the "Align orbital plane" MFD for eliminating any residual inclination).

The next step is to catch up with your target, by modifying your orbit appropriately. Use the "Sync Orbit" MFD for this.

C4. I can get close to the ISS, but haven't succeded docking

Once you got close to your target (see C3), use the Docking HUD mode and the Docking MFD for final approach. The Docking HUD contains relative velocity indicators which help closing in on your target. You need to tune your navigation radios to the target's transmitter frequency to make use of the docking instrumentation. (You can find the target's transponder frequency (XPDR) in the vessel info sheet (Ctrl-I). Set one of your navigation radios (Shift-C) to that frequency, and slave the HUD and Docking MFD to the appropriate receiver).

In the final approach stage, switch the nav receiver to one of the target's IDS (instrument docking system) frequencies, if available. This will activate approach path indicators in the HUD, and docking indicators in the MFD, to guide you to your final docking position.

C5. How can I get from Earth to the Moon/Mars?

Orbiter now includes Duncan Sharpe's TransX MFD mode, which is a great tool for setting up interplanetary routes. You need to activate the TransX module in the Orbiter Launchpad dialog to use this.

TransX is quite a complex navigation tool, so to understand the concept and options, make sure you read the TransX manual (in the Doc folder) carefully.

C6. I want to see imperial units instead of metric

All internal calculations performed by Orbiter are done in metric units (metre, second, kilogram, Joule, Pascal, etc.), for the simple reason that this is the only system I am familiar and comfortable with, and it is widely used by the scientific community. Likewise, all standard instrument readouts and data displays are in metric units (with very few exceptions, like the use of astronomical units (AU) for large distances). There is however nothing preventing an addon developer from implementing instruments which display their data in a different unit system, and it would be entirely possible to write imperial unit replacements for all standard MFDs. Just don't expect them to feature in the stock Orbiter distribution. If you want to see feet, fathoms, stones, barns or quarts, you will probably have to code them yourself.

C7. Why does the moon look so small?

The moon, as seen from Earth, covers an angular diameter of approximately 30 arc minutes (at a distance of ~385 000 km and diameter ~3 476 km, you can work it out for yourself). This is exactly the size at which it appears in Orbiter. There are two possible reasons why it may appear too small to you:

Too large field of view setting. If you want to see the moon and other objects in the simulation window at the same angular size as you would, for example, when looking out of a window, then the field of view (FOV) setting of the simulation must correspond to the viewing geometry. That is, the simulation window size and eye-screen distance. As a typical example, for a 19 inch monitor (4:3 aspect ratio) running Orbiter in full-screen mode, and a viewing distance of 60 cm, the correct (vertical) FOV setting would be 27 degrees. In practice, a much larger value is usually selected, to compensate for missing peripheral vision.

Optical illusion. People perceive the size of the moon to be much larger than it really is, in particular close to the horizon. Several explanations have been brought forward. You might want to take a photograph of the moon yourself, with a normal-focus length lens and including some trees or houses for reference. It is going to look smaller than you thought!