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Ishiaki edited this page Oct 12, 2026 · 1 revision

Warm Start: the long description

The front page is kept short. This is what it said in full until 2026-10-12, when it was cut down: what the mod does at length, what is good to know, and what was tried on each system. Nothing was lost in the cutting.

Kerbal Space Program starts in less than half the time, because what it works out afresh at every start is kept from the last one.

From starting the game to its main menu: 55 seconds as the game ships, 21 with Warm Start (measured)

Where the seconds of a start go, as the game ships and with Warm Start

For Kerbal Space Program 1.12.x. Needs Keystone, a separate download (its page on SpaceDock): this mod does not load without it.

Three things take most of a start, and each comes out the same every time:

  • The expansions' files. Making History and Breaking Ground keep their models and scenes in three files that the game unpacks whole, into memory, at every start. A copy of each is kept that needs no unpacking.
  • Textures. Every PNG picture is unpacked and squeezed into the graphics card's own format, every time. What the game makes of each is kept, and handed back. The DDS pictures, which are finished already, are read by several threads at once.
  • The small bundles. The game opens each of a couple of hundred small bundles (its manual's pages, mostly) to read a short description out of it. The descriptions are kept.

None of the game's code is changed, and what the game ends up with is what it makes by itself: that was checked texture by texture and description by description.

Install

Install Keystone first: it is a download of its own, and its Keystone folder goes into your KSP GameData. Then copy the WarmStart folder from this mod's download into GameData beside it.

The first start after that is as slow as ever, and at its main menu a minute of work goes on in the background (a line at the foot of the screen says so). From the second start on it is fast.

What it costs

About a gigabyte of disk, in GameData/WarmStart/PluginData: three quarters of it the expansions' copies, the rest the textures. Deleting that folder loses nothing but the time to make it again.

It costs no memory. With it the game used 1.2 GB less here (7.0 GB against 8.2), because the expansions' files are no longer unpacked into memory whole.

Settings

In the Keystone window (the keystone button on the game's toolbar, or Option-K on a Mac, Alt-K elsewhere). Each part can be switched off by itself; what is kept stays on the disk.

Setting Installed as
Warm start on off: the game starts as it always has
Textures, ready made on PNG pictures kept as the game made them, DDS pictures read ahead
What is in the small bundles, kept on the descriptions the game reads out of its small bundles
The expansions' files, unpacked on the copies that need no unpacking (most of the disk)
Do not wait on the loading screen on the loader does not slow down while one loading picture fades into the next
Load at any frame rate on the game's frame-rate limit is lifted until the main menu is there

The page also says how long this start took, and the last one without anything kept. And (from 0.2.0) where the start went, mod by mod: which mods' parts, models, pictures and sounds the seconds were spent on, so that with hundreds of mods one can see which are worth their wait.

Good to know

  • When a file changes (a mod updated, added or taken out), only what was kept of that file is made again, in the start that follows.
  • It does not make everything faster. The game's own start before any mod runs, its parts, and its planets and space centre take 17 of the 21 seconds that are left on the Mac, and are left alone.
  • With KSP Community Fixes installed, which loads the game its own, faster way, Warm Start does nothing: use one or the other.

Where it works

System
Mac Made and measured here (Apple silicon, the game under Rosetta, OpenGL, 2026-10-08): 55 s to the main menu as the game ships, 21 s with it.
Windows Tried on Windows 11 (KSP 1.12.5, Direct3D 11, 2026-10-09), the game on an SSD: 47 s to the main menu with it switched off, 17 to 18.5 s with it; 18.3 s with the game started on OpenGL (-force-glcore).
Linux Never run. It is plain C# with nothing of one system's in it.

More: how it works, what was measured and what was tried.

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