Invisible Crystal Spheres
by HåvardThis is one of my theories for adapting some of the elements from Spelljammer into the Mystara cosmology. A central point here is to adapt ideas from Spelljammer to Mystara, not the other way around.
As in the Spelljammer Universe, solar systems are surrounded by Crystal Spheres. However, these Spheres are invisible and usually intangible. Passing through this unseen barrier normally wont even be noticed by the crew, being no obstacle to a vessel on its way into normal space.
Certain parts of the Crystal Sphere, however, in areas where the planets cast their "shadows" on the sphere, dark spots form. They are hard to see upon the blackness of space, but they are actually gateways leading to the Phlogiston, a sort of "Hyper-Space" allowing ships to pass from one world to another in much shorter time than they would travelling through normal space. Only a skilled Void Navigator is able to locate these Void Gates.
Vessels in the Void
There are many kinds of vessels used to travel across the Void. Spelljammer ships are extremely rare near Mystara Space, and they are expensive and limited in their use. Most Mystaran vessels rely on fly spell enchantments. These can travel much faster in the Void than they are able to within the atmosphere. Some Voidships have great sails that harness the Solar Winds. However, these are also limited in use since Solar winds make it hard to sail towards the sun. Other ships use enchanted sails that push the ship forward.
Elements from Spelljammer and Other Settings
Although I have decided to use elements from the Spelljammer setting, I normally advice against incorporating other settings (especially the Forgotten Realms, Greyhawk, Dark Sun, Dragonlance, Ebberon etc.) if you want to keep true to the Mystaran feel. The meta-setting of Spelljammer however, can easily be adapted to fit with the Mystara cosmology.