Gravity appears to be an attribute of space itself and can not be shielded, but a directional gravitational forces can be generated to cancel out the local gravitational force (or even reverse it). In a certain sense a conductor does not really shield the object in the conducting box either. It mearly produces a field opposing (canceling) the external field inside the box.

The static fields are not too useful for propulsion. 1. They are always attractive. 2. They require large amount of matter to generate a significant field. 3. They can not generate an non-conservatice force (against space) field to propell a spaceship.
There is another field in electro-magnetism called the magnetic field. The magnetic field is generated by the motion of charge. The counter part of this field in terms of gravity would be a motional gravitational field (Mg). Thus a rotating mass should produce a motional gravitational field. This field would have properties analogis to the magnetic field such as a directionality (the axis of rotation).
An accelerating charge produces elecromagnetic radiation. It does so because the fields generated by the particle carry information to the rest of the universe about the location of the particle. When the particle accelerats, its position changes. Since the fields propagate at a finite velocity, they produce a propagting disturbance in the space-time. In electromagnetism this disturbance propagates at the speed of light. (and is light, micro-wave, RF {radio frequency}, x-rays etc.) If gravity propagates at a finite velocity, it to must produce a gravitational radiation.
Newton's law F=ma tells us it is impossible to produce a force against nothing. If vacuum space were nothing (which we know to be untrue) it would be impossible to propell an object by pushing against space itself. Actually the inertia of matter comes from matter interacting with space-time. By using a time changeing of acceleration or 'Hyper Accaleration' it is possible to produce a force against space. Many inventors have built and demonstrated deviced that to just that. This technology is call inertial propulsion.

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