How start on Asteroid

• Rimworld 1.6 with Odyssey DLC
  
• something to edit the XML file (eg. VScode, but Notepad could work too)

Create copy of Gravship scenario (feel free to disable pursuing mechanoids if you want) and save it.

Go to %userprofile%\appdata\locallow\Ludeon Studios\RimWorld by Ludeon Studios\Scenarios in explorer and open your saved scenario file with prefered text editor.

Find part that looks like this:

<li Class="ScenPart_ForcedMap">
<def>ForcedMap</def>
<mapGenerator>OrbitalRelay</mapGenerator>
<layerDef>Orbit</layerDef>
</li>

and replace OrbitalRelay with AsteroidBasic

Save your file, then go into Rimworld, and now if you Load your saved scenario when creating new game it will start you on an Asteroid :)