Lighter than air vehicles.
For the same reasons blimps don't rise indefinitely.
Yes.
Quote from: "Tom Bishop"For the same reasons blimps don't rise indefinitely.human controls ensuring that proper density is maintained at the correct altitude?
of course the controls are heavier than air, but the vehicle as a whole would not have to be.look at the pods on blimps which are defiantly heavier than air, yet blimps fly.
Blimps are normally controlled by people at very low altitudes. Satellites, on the other hand, are not.