VRTK is a Toolkit that we used mainly to implement the interaction with the User Interface and the objects in the space using the controllers of the HTC VIVE. It is compatible with the SteamVR library for Unity. It has been useful particularly the feature of the simulator of a VR headset with its relative controllers to test our project on our PCs even without a VR device.
We found on the web textures that can be applied to identify different planets in the 2D view and in the 3D models. They have been found by searching on celestiamotherlode.net. For planets from our Solar System and for the stars we used the textures already present in Andy's sample project.
We used a very immersive background song that accompanies the user in a total experience inside our VR application. It was found on a YouTube video of a game and downloaded, because the author made it publicly available for download.
As an additional feature we added a space platform on which the user can move across the systems and inside the 3D model of all the stars, feeling like he/she is really flying around the space. The model for the platform has been downloaded on the site turbosquid.com.