Hi Cayliff. I haven't tried that exact thing with Unity, but I will tell you what I know:
- Yes, you can make asteroids with tunnels through them. You would have to model them using a normal 3D modelling program.
- Yes, you can allow the ship to collide with them (inside and outside). Note that collisions with complex meshes can be a little unreliable. If I recall correctly, Unity's Collider system works best with convex shapes. So you could create a set of convex Colliders which overall add up to the complex shape of the asteroid with tunnels through it.
- Asteroids could collide with each other, but I suspect it would be more tricky because of the odd shapes. It also depends whether you want the asteroids to break up when they collide, which would required custom modelling and perhaps scripting, e.g. making one asteroid out of a bunch of models connected with Joints which can break when hit hard. Or manually destroying the asteroids and instantiating new "blown apart" objects.
- Note that to allow collisions you need a RigidBody and a Collider. A RigidBody is affected by physics, a Collider is something that it can hit. An object may have both.
- Standard "downwards" gravity can be turned off. If you want your own outer space gravity (e.g. asteroids attracting each other) you can manually calculate it and add forces to each RigidBody, but it would get very slow if you have too many objects, because every object can affect every other object.
Unity has its own Mesh Collider that mimics the shape of the mesh and changes that into a collider. Works fine, but as said, convex shapes are better for large objects.
Truth be told, you can do anything with most Game Engines -- the monumental question is usually "How?". With Unity that question can be answered via the helpfull forum and robust reference pages. Still, some questions are tougher than others, and whether your game will work or not depends on your experience, the design itself (clever design will not bump against limitations while still being awesome) and the dedication you put into your work.
Disclaimer: Each my post is intended as an attempt of helping and/or brining some meaningfull insight to the topic at hand. Due to my nature, my good intentions will not always be plainly visible. I apologise in advance and assure I mean no harm and do not intend to insult anyone, unless stated otherwise
It is the year 3019 and we have used all the metal resources on earth. To get the resources earth needs we had to look somewhere else. So we looked at the astroroid field to get the resources we need. The two major corporations that mines the astroroid fiels is the Malon Corp and the Ditrix Corp and they fight to control the astroroid field. Since its not on earth there is no rules or laws. Each corperation has decided to build a fleet of warships to fight against the other corporation. This fight goes on until they find out they are not alone. and they decide to fight together not just to protect the astroroid field but there homes on earth.
This takes place between the orbits of mars and jupiter and arround boths planets and there moons