To install Sector Space mods via SSFML, drop the SSFML jar into the Sector Space install folder, install Java 25, point Steam's launch option at the SSFML jar ("Path to SSFML.jar" %command%), drop each mod .jar into the mods folder, and set each entry to enabled=true in mod_list.cfg. Restart through SSFML every time you change the config.
More context
Launching through SSFML does not track Steam stats, so leave the launch option off and disable every mod for achievement runs. Back up saves before the first modded launch because unmodded play can convert modded content into Null items until you boot back into the same modded session.
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Install Java 25 and SSFML
Download SSFML and Java 25
Step 1 is to download the SSFML jar (Nexus is the standard release, GitHub hosts a fork with experimental features), then download a Java 25 SDK.
Done when: You have both an SSFML .jar and a Java 25 SDK ready to use.
Drop SSFML into the install folder
Step 2 is to drop the SSFML jar into the Sector Space install folder, easiest at steamapps/common/Sector Space, though it can technically be installed anywhere.
Done when: The SSFML jar is in your Sector Space install folder.
Run SSFML once to create the mods folder
Step 3 is to double-click the SSFML jar to run it; the loader installs its libraries and creates a mod folder in the game directory. Step 3.5 is to manually create steamapps/common/Sector Space/mods if the loader did not.
Done when: A mods folder exists inside the Sector Space install directory.
Force Java 25 if the jar will not open
Step 3.6 covers the case where the jar does not open the game: force Java 25 by creating a .bat with jdk-25.0.2\bin\java.exe -jar SSFML.jar + pause. Mod files in the mod folder should be .jar files, not .zip.
Done when: You have a working .bat or shell script that boots the game through SSFML with Java 25.
Add mods to the mods folder
Install mods from Nexus or Discord
Step 4 is to install from Nexus or Discord channels. Drop each mod .jar into the mods folder. Mods placed inside the mod folder are disabled on load by default and must be re-enabled in the mod_list.cfg file, after which the game is restarted to apply changes.
Done when: Each mod .jar is sitting inside the mods folder.
Enable each mod in mod_list.cfg
Open mod_list.cfg in a text editor, set each installed mod to enabled=true, and save. Restart the game through SSFML for the changes to take effect; running the unmodded Sector Space.exe will skip the mod folder entirely.
Done when: Each mod you want active reads enabled=true in mod_list.cfg.
Point Steam at the loader
Step 5 covers Steam launch options: launch the game through Steam play with "Path to SSFML.jar" %command%. Replace "Path to SSFML.jar" with the absolute path to the loader jar, including quotes. Steam will then call SSFML on every launch and SSFML will boot the actual game.
Note: launching through SSFML does not track Steam stats. If you need stats tracking for an achievement run, launch Sector Space directly from Steam without the launch option and disable every mod first.