The term "gravitational engineering" calls to my mind at least large earth moving equipment, hauling tons of rock and soil in a load, excavating the entire side of a mountain. It evokes images of heavy duty machines, carrying very heavy loads, large scale construction projects, and the shaping and reshaping of the features of the earth on a fairly large scale.
Human beings so far have paid little direct attention to the notion of gravitational engineering, which can be defined in terms of the development of working systems based upon differentials of gravity and gravitational energy, though we have long deployed forms of gravitational energy in our energy production processes. Dams and water-mills that are powered by the downward flow of a stream of water are examples of common gravitational engineering applications--indeed the use of dams for power utilizes gravity both in the production of water in a long water column to drive generators, and in the filling of the reservoir from watershed produced by rain-fall. We can look to simple inclined planes, levers, pulleys and gears as working systems based indirectly upon differential distribution of weight produced by gravity. Less obvious are systems that depend upon water pressure and or geothermal energy produced by the pressures generated by the earth's crust to produce steam or other forms of heat energy. Alternatively are the use of tidal differentials of the oceans and large bodies of water created by the moon's gravitational pull. Even less obvious are applications like the use of "lighter than air" gases as a form of buoyancy to create aerodynamic lift, or similarly, in the water, the use of gas to create similar buoyancy to lift otherwise heavy objects from the bottom of the sea floor. Rockets that travel to space beyond the grab of the earth's gravity, and airplanes that use aerodynamic lift to suspend them in the air in motion, provide alternative examples of mechanisms that are used to counter the force and pull of gravity that is, on earth, forever earthward.
I would assert the claim that we have otherwise paid very little attention to the possibilities of alternative energy systems created by the continual presence of gravity upon earth. It is possible for instance to systematically exploit the differential in lifting a mass along a low inclined plane, especially under conditions involving minimal friction, to a level that we can exploit the differential energy created from a free fall or accelerated descent downward. We can alternatively exploit the possibilities of hydraulics to lift large masses by means of very small but steady inputs of energy, and realize gain created by the potential energy created by a large, elevated mass. We cannot create perpetual cyclical systems that defy the laws of thermodynamics, but we can take into account the principles of gravitational dynamics to balance the books of the energy budge of nature in our favor. Heaving a well aimed rock at a distant window in an effort to shatter it attempts to convert the mechanical energy transmitted from the arm to the stone, into a form of gravitational energy that combines the momentum of the velocity and weight of the rock that is created by its descent to earth. Those who know how to ring the bell at a carnival game by swinging a large hammer or mallet, know that the use of gravity in the fall of the mallet-head creates the necessary energy to ring the bell, when muscle power alone cannot reach half the height. Similarly, before the advent of Trebuchet's in classical siege-castle warfare, reliance was not upon the use of gravity to fling a stone, but upon the use of energy transmitted directly from some device, like a bow, or an crank or spring, to the projectile. The advent of the Trebuchet transformed such warfare in the couple of centuries before the arrival of gun-powder. With gun powder large siege mortars that fired projectiles in a high arc of trajectory made up in destructive power what they lacked in range and accuracy, and larger long range cannons that could hurl larger projectiles further, tended to increase the destructive capabilities of the projectiles not just from their explosive content, but from their acquired gravitational energy.
We can stretch our definitions a bit and add to this growing list the use of pendulums and fly-wheels for the inertia they maintain and their gyroscopic stability that seems to defy the laws of gravity at every point except at the center of the system where its axis touches or connects with a support.
In none of the cases above, except perhaps in the use of dams to create extremely high water columns, has the use of gravity been deliberately exploited, in and of itself, as a means to create an overall gain of additional energy in a working system. Therefore, it stands to reason that there is yet room for considerable development in this direction, if we pursue it innovatively and inventively. I have myself devised on paper several different possible mechanisms in this regard, and I think the object and lessons of a course in gravitational engineering can be extended and elaborated to include such principles in the design of new vehicles, power generation systems, power-train and transfer systems, and even in the potential for the directional measurement and detection of gravitational energy on a fine scale.
I will make a simple set of propositions that makes the concept of gravitational engineering possible, if not completely efficacious--
1. a total gain in energy can be created from the free-fall or accelerated descent of a heavy mass, representing the potential energy of that mass at a given elevation, over the total amount of energy that was mechanically expended, in efficient systems, to achieve the elevation of the object in the first place.
2. the gain in energy that is created by such a gravitational descent of an object may be efficiently transferred into a form of mechanical or other energy that can be utilized or reutilized for purposes of production.
3. potential gravitational energy achieved by the effective elevation of an object may be indefinitely stored and accumulated until needed.
4. gravitational energy is continuous and always available--it is essentially boundless. It occurs in unlimited supply, if we can capture it, and it occurs in a manner that can be considered to be anti-entropic.
I would assert that under the right conditions, we can create a continuous gain of net energy output compared to the working energy input, less the friction and energy loss involved in the operation of the system, in such a way that we can make such systems highly productive in the long run. In gross terms, such a system might have to be very large, to produce quantities of usable energy that would make such production worthwhile a scale, but it is possible to build a mechanism as fine as a watch that can produce gains in gravitational energy in small and measured doses.
The possibilities of gravitational engineering beyond earthbound conditions takes on new meaning, and in deep space where gravitational force in any one direction tends to be weak or muted out, the problem of such engineering in relatively gravity-free environments, without gravitational mass, becomes a central issue. If we are to extend the idea of gravitational engineering to other planets, for instance, such as the moon, or Mars, where gravity is about half of what it is on earth, or on a planet like Saturn or Jupiter, where gravity would be much greater, new sets of problems would arise.
But for the time being, the problem of gravitational engineering remains mostly an earthbound one. It involves, among the variables listed above, the problems of countering the effects of gravity, especially in terms of being able to escape the hold of gravity beyond the earth's gravitational boundaries, especially in a manner that is cost effective and efficient. This problem has received considerable attention, especially in the last decade, and warrants further research and involvement.