I played with this mod yesterday and decided to experiment with space science. However, when I tried to launch the space platform starter kit, I couldn't do it. I started to figure it out and it turned out that I was locked on the starting planet. Because the platform is created above Nauvis, where I simply don't have access. Thus, it turns out that I can't leave the starting planet in any way. After all, in order to leave it, I have to start creating space science, but as I said above, the platform is created not above Vulcanus, but above Nauvis.

Oh, and I forgot to say in the title that the starting planet is Vulcanus. I play with many mods, but they are very unlikely to affect this kind of softlock.
Edit: The culprit has been identified. The Editor Extensions mod does not allow you to create a platform above Vulcanus. I found this out experimentally:
First, I disabled all mods except the standard ones and yours, then I enabled EE, and it immediately turned out that it was blocking the creation. For the final check, I enabled absolutely all mods except EE - and was able to create the platform without any problems. You have been given a tip, I am waiting for a fix.