Afew more things in general and about this tutorial
If you got KSP on Steam, it is recommend to move the game directory out of the Steam directory to prevent auto-updates! It is not possible to deactivate updates on Steam but a new game version may break a mod and/or your (modded) savegame, so you definitly don't want to update the game before you know if all your mods will still work fine or got updated.
Keep in mind that many mods which are compatible with KSP 1.4.x, are still compatible with 1.5.x and 1.6.x. If you play on 1.5.x or 1.6.x and the mod you want to install isn't available for your specific game version, you can still try an older mod version with good chances of success
For most parts of this tutorial, I'm going to use "SCANsat" as an example, for various reasons
Before you install a mod, you should know your game version so you can get the corresponding mod version. If you are not sure which game version you got, launch the game and take a look at the lower right corner in the main menu:
On Spacedock, you can download the latest mod version via the "Download" button and the compatible game version is listed in the information panel. If you need a different mod version, open the "Changelog" and Spacedock will present every previous released mod version to you, together with the game version it was build for:
The "Release" section looks a bit differently but the latest version will always be the first entry. Old mod versions are available as well but there is not always the corresponding KSP version number listed. Sometimes it can be found in the mod name or the changelog of a release. To download the mod, just click on the link for the .zip archive:
Quite a few mods require one or more other mod(s) to run properly or at all, these "other mods" are called dependencies. A distinction is made between hard- and soft dependencies:
Hard dependency: Required with no exception. If you don't install a hard dependency, you'll experience crashes, errors and misbehaviour of the mod.
Soft dependency: Required for additional features but not necessary to run the mod.
First of all, you need to find and open your KSP install directory. The install location depends on your system and where you bought the game so if you don't know where to look at, search your system for the "KSP_x64.exe". Keep a window with your KSP directory open.
Mods are usually distributed within .zip archives. You can un-zip the archive in a separate folder or unpack the files directly where they are supposed to be, that's up to you. I prefer the latter method
Open the folder/zip file of the mod in a separate window and place it somwhere next to the window which shows your game directory. Now, there are two cases which can happen:
Case 1: The mod folder comes with a "GameData" folder
As pointed out by @MaltYebisu, this method doesn't work on MacOS. Mac users, please scroll down a bit and read about case 2
If the mod folder contains it's own "GameData" folder, you can drag and drop it directly into your game directory, which also contains a "GameData" folder. This will merge both folders together (should work on each operating system):
On a sidenote: Some mod authors who wrote/maintain multiple mods, uses an additional sub folder for all of their mods (for example: Kerbal Alarm Clock and Transfer Window Planner). Don't worry about this, just treat them like the mod in the case 1 scenario and merge the folders together
(Case 3: ModuleManager)
"ModuleManager" (MM) is powerful mod on it's own and a common dependency for many other mods but so far, the install instructions don't fit for MM. It is a little bit special in two ways: First of all, you will not find a release version within the github repository, on SpaceDock or CurseForge. In order to download ModuleManager manually, you have to visit the MM thread here in the forum:
If you cannot find your KSP version in this list, follow the instructions in the MM thread.
Also, MM is distributed as a plain .dll file and to install it, you have to place the "ModuleManager.dll" directly within the "GameData" folder of your game....no sub folder or anything else, just like this:
(Picture was added quite some time after I wrote this tutorial, please don't get confused by the different mods which are installed here, compared to previous screenshots)
That's already everything you have to do, MM is now installed properly
CKAN is a powerful and very well supported tool to manage your mods. You can install, update and remove mods with just a few clicks and even dependencies are handled automatically. It is available for Windows, Linux and MacOS and can be downloaded here:
CKAN automatically searches in some default installation paths for KSP, but if you followed my recommendation from the beginning and moved it somewhere else, you need to add it manually. Click on "Add new", navigate to your KSP install and select the "buildID64.txt".
On the first run for a new KSP install, CKAN will also ask you if you want to update the modlist and repository on each launch. I would suggest to allow both options so you are always up-to-date but it's up to you:
By default, all mods which are compatible with your KSP version will be listed. Since the list will be pretty long, there are some search options available like "mod name", "author" and "description". You can also decide which mods are listed in general by setting up the filter:
Now, the "Apply changes" button becomes available. Click on it, to display the changeset (you can also click on the "Changeset" tab). In this example, you will notice that ModuleManager will be installed as well even though we didn't select it manually. ModuleManager is set as an dependency for SCANsat so CKAN will install it automatically:
Hit "Apply" in the lower right corner to proceed.
The next two steps are optional, it depends on the mod you want to install:
Some other mods may be recommend or suggested to use along with the mod(s) you want to install. The main difference between those options is the pre-selection: Recommend mods are "opt-out" and suggested mods are "opt-in". In both cases, you will find a button in the lower left corner to select or de-select all mods from these lists.
If any of these lists appears, pick your choices and click on "Continue" to proceed.
If you want to uninstall a mod, just unselect the mod in your list and repeat the installation steps.
Dependencies are not removed automatically but if you remove a dependency, every mod which depends on it will be removed as well!
Compatible KSP Versions
by default, CKAN will only lists mods which are compatible with your game version. Since many mods which are compatible with 1.4.x still work fine in 1.5.x and 1.6.x, you can allow CKAN to show and install these mods as well:
Dependencies are marked with a "star", recommendations got a "thumb up", suggestions are marked with a "i" and conflicts are marked with a "!". If a mod name is highlighted red, it is not compatible with your game version (if it's a dependency, you cannot install the mod!). You can double click on these mods to find the corresponding CKAN entry.
Versions provides a list of all available mod versions. Compatible versions are highlighted and if you want to install an older mod version, just double click on the list entry. If a newer version is already install, you need to remove it first.
The red highlight indicates a mod that's incompatible with your KSP version. Obviously that's good news for conflicts, since it means you aren't at risk of installing both, but if a dependency turns red then that'll block installation.
As far as I know, the installation procedure is the same on each operating system. The game still got a "GameData" folder, which is everything you need for the manual installation, and CKAN runs on a mac as well.
Once you are aware how mods work in KSP, you will less likely make mistakes trough (un)install of mods. More than 90% of bug reports comes from faulty installs somewhere. So, if you encounter some bug, be nice to mod authors and double check your installs before reporting issues. Install mistake may happen to new KSP players as well as veteran players. No wonder, considering the number of mods available and when you want to install significant number of mods it may be tedious and tiresome process that can lead to mistakes.
Actually, I honestly thought this is the correct spelling and I'm writing it this way since always (three times just in the OP)... I'm quite surprised you are the first one to correct me Thanks!
If the mod folder contains it's own "GameData" folder, you can drag and drop it directly into your game directory, which also contains a "GameData" folder. This will merge both folders together (should work on each operating system):
If you do that on macOS, you will not get the option to merge. You only get the options 'stop' and 'replace'. If you choose 'replace', the entire GameData folder will be replaced entirely (deleting the Squad folder and any mods you have installed).
I would like to say that direct install is much better e.g. planet mod lags the game, remove a few planets, currently im playing using, KW rocketry, Restock +, Kerbal Reusability Expansion, KSP interstellar, Extrasolar, Galaxies Unbound, Kopernicus
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