The Gravity Drive was another theory before the discovery of SubSpace. Contained onboard large capital ships (no current Terran ship has been designed large enough to carry the Gravity Drive ), the Gravity Drive is essentially a monstrous partical accelerator. Inside the accelerator, Helium and Hydrogen ions are crashed into each other with such force that the elusive Z-particle. The electrical charges created by the collision cling to the Z-particles, increasing the mass and gravity.
After only a few seconds of this process a critical mass begins forming in the accelerator and the particles must be ejected. High Density Transfer Tubes carry particles from the accelerator to a "staging area," where they are lined up by charge. When the magnetic poles of the particles align, they are fired into space immediatly in front of the ship by means of high powered lasers.
Once a concentrated beam of particles is fired space begins to distort. The heavy gravity of the ionized Z-particles is so great that space itself folds into the beam. As the particles continue to be ejected space begins to "tear." This "tear" creates a controlled black hole functioning similarly to Jump Nodes. The exit "Node" is determined by the intensity of the partical beam.
In theory, the Gravity Drive could create an exit from Sol, however no current Terran laser is powerful or large enough to fire the partical beam. The super turrets aboard Orion Destroyers can only handle 5-8% of the energy load from a Gravity Drive.
Unless we lear better ways to harness laser capabilities, the Gravity Drive is not an option for reopening the supply routes in Sol.