In all honesty, I haven't found a resource for disabling asteroids all together; I'd like to disable them.

Otherwise, I would like to decrease the spawn rate of asteroids by as much as possible. Is 10% of the default the absolute limitation?

I'm not sure if space platforms can really function without any asteroids whatsoever? Is this an attempt to reduce the amount of lag in the game? Or did you mean to reduce the amount of dangerous asteroids (since there's no other reason to completely eliminate the asteroid chunks).

The minimum percentage isn't anything hardcoded, it's just what seemed to be minimum viable amount for space platforms to use for fuel to propel themselves.

I'm honestly surprised that there isn't a mod on the portal to completely disable all asteroids, it actually wouldn't be that difficult (instead of multiplying the spawn probability, could set to zero, or just remove the field entirely). I'm not sure how viable that would be.. you would have to use rockets to mail in all the resources you need to propel the platform to the next destination, or else just let it drift after it runs out of fuel

EDIT: Hmm, looking further into this concept, it would be basically impossible to create space science, since there's no way to create carbon or ice in vanilla (you don't get the alternate recipes until you reach the other planets), which locks out thruster and planet discovery techs. Would need to create some kind of alternative in order to make the concept work

All that being said... I think this might be possible with Muluna? Since it moves the thruster earlier in the tech tree, allowing the player to reach Muluna, which provides access to asteroid mining and processing using resources from the moon instead of directly from space. Here's a concept test that no longer requires Muluna, uploaded via Google Drive

Personally, I'm making a custom map where enough tech is unlocked that its viable and requires on-planet production to sustain ship travel.

The general idea is that players can unlock resources through sabotaging AI bases, but they won't have access to raw materials to produce anything themselves until much later. Planets provide certain raw materials that changes typical progression.
Nauvis : Water
Vulcanus : Coal
Gleba : Iron
Fulgora : Copper

Besides that, it sounds like a fun change for my megabase.

Edited and updated the asteroid-disabling concept mod in the Google Drive link, removing the muluna requirement (and adding a new thumbnail), for your testing.

I might release it on the mod portal in the future, though it would be pretty much useless without other mods that allow the game to be completeable without asteroids, since it would also remove promethium asteroids, thus no promethium science