how do install old versions of KSP I wanna install 1.3.1but don't know how

[i wanna play with mods]

how do i install them

[Lisias]

40 minutes ago, i wanna play with mods said:

how do i install them

The hardest part is to download it.

Where did you bought KSP?

[DeadJohn]

This link summarizes how installing old versions works for different online stores. If you need more help, please let us know where you bought the game. https://support.privatedivision.com/hc/en-us/articles/360037243914--Kerbal-Space-Program-Is-it-possible-to-download-old-versions-of-KSP-

Why go all the way back to 1.3.1? What must-have mod requires such an old version?

Edited September 9, 2021 by DeadJohn

[Lisias]

3 hours ago, DeadJohn said:

Why go all the way back to 1.3.1? What must-have mod requires such an old version?

One possible reason is having an old rig. I play KSP since the 1.4.0, and on 1.4.3 with the new PQS system KSP started to overtax a bit my older rig (mobile i5 sandy-bridge and HD3000 gpu).

The difference were significative, but not enough to prevent me from  playing 1.4.5 for a lot of time (I essentially jumped all the 1.5 and 1.6 and gone straight to 1.7.3).

However, the 1.4 series broke a lot of add'ons, mainly due the change from Unity 5 to 2017, and so there's little incentive to play KSP 1.4.1, 1.4.2 or 1.4.3 (1.4.0 was terribly buggy). But since only 1.4.5 is available for downloading nowadays (what I think it's a mistake - KSP 1.4.3 with Making History is very playable on my older rig), 1.3.1 ends up being the best (if not the only) choice.

Edited September 9, 2021 by Lisias
ERRATA: the PQS was changed on 1.4.4.

[i wanna play with mods]

21 hours ago, Lisias said:

i bought it on steam

i bought it on steam

Edited September 9, 2021 by i wanna play with mods

[i wanna play with mods]

4 hours ago, DeadJohn said:

This link summarizes how installing old versions works for different online stores. If you need more help, please let us know where you bought the game. https://support.privatedivision.com/hc/en-us/articles/360037243914--Kerbal-Space-Program-Is-it-possible-to-download-old-versions-of-KSP-

Why go all the way back to 1.3.1? What must-have mod requires such an old version?

i bought the steam ver

[Lisias]

1 hour ago, i wanna play with mods said:

i bought it on steam

Locate the KSP on your Library, right-click on it and select Properties.

Then Select the BETA tab, and search for the version you want to use:

From now on, your Steam maintained KSP copy will be downgraded to that version.

I strongly suggest that you do a copy of the KSP installment to some other place before modding it - modding installments handled by Steam is a source of head aches, trust me on this.

Cheers.