[ninty]

The whole train in a vacuum thing held the point that in order to achieve top speed, it would have to gradually speed up using different sections of the tunnel that are closed off to the vacuum to gain speed, then once at the right speed, entered into the vacuum and achieving its top speed.

And i'm not going to argue over the definition of inertia, because you just stated it and there would be no point to that.

Yes the shuttle when in orbit is affected by gravity. Thats what keeps it in orbit. If there was no gravity, there would be no orbit. However the further away you go, the less gravity. If someone stands on a mountain and someone at sea level, the weight of the person at the mountain will be less.

Anyway bottom line is I think its very possible to travel to mars alpha centauri or other stars at or near the speed of light.