Gravity is the bane of aerospace transportation. The force of the Earth’s gravitational field acts to pull all objects, whether in motion or at rest, downward toward its surface. Because aerospace transportation involves the motion of vehicles through the atmosphere and into space, propulsion engineers are faced with the requirement that aerospace vehicles will have to carry enough propellant and associated infrastructure in order to provide enough propulsive thrust to overcome the downward pull of gravity and achieve rectilinear motion. Energy has to be expended by a propulsion system to overcome the force of gravity in addition to providing for rectilinear motion, and the majority of propulsive energy is dedicated to overcoming gravity. The propulsion engineer is faced with two choices for the control of gravity in this regard: passive control and active control. Modern aerospace propulsion technology, which is based on accumulated scientific knowledge since recorded history, can only achieve the passive control of gravity whereby a given propulsion device must develop a thrust that will passively counteract the Earth’s gravitational pull, lift a vehicle off the surface, and propel it through the air or into space. Newton’s laws of motion and gravity require that the fuel fraction of any vehicle can never be less than that given by a simple function of the ratio of the vehicle’s maximum speed to the speed of its rocket plume, jet, fan, or propeller wake. For example, this limit implies that a single-stage rocket that accelerates to escape velocity must be composed of more than 93% fuel. That is because a rocket must accelerate its working fluid from rest (relative to the rocket) up to its exhaust speed. Thus, exhaust speeds for aircraft and chemical rockets are limited by material science, chemical reaction rates, and engineering factors to only a few thousand meters per second.
To date, there is no technology that can achieve the active control of gravity. If one could nullify or otherwise control the Earth’s gravity field, then one has the ability to dramatically reduce the amount of propellant, its tankage, and the overall structural size and mass of an aircraft or rocket because there will no longer be any need for these to overcome the pull of Earth���������������������������s gravity when transporting a payload across the globe or into space. Instead, aerospace vehicles will only need to have the propellant mass and infrastructure necessary to change their kinetic energy from rest to a final velocity necessary to achieve atmospheric flight or space orbit. The Earth’s gravitational field will no longer have any impact on aircraft, launch vehicle, or spaceflight dynamics if one were to achieve active gravity control. Aerospace vehicles would merely “levitate” in air or push themselves away from the Earth’s surface and their propulsion systems would be optimized for change-in-velocity missions, and so we can abandon the standard rocket equation. However, it is possible to envision a form of active gravity control propulsion that would not require a change in kinetic energy.
One of the primary concepts for active gravity control is antigravity, which is technically defined as a repulsive gravitational force. If antigravity exists, it can be exploited to counteract or nullify the gravitational pull, or attraction, of a planetary (or stellar) body that acts upon a much smaller body. Einstein’s General Theory of Relativity gives a prescription for a variety of different antigravity concepts. Even Newton’s law of gravity offers several different classical prescriptions. We can use Newton�������������s law of gravity to simply nullify the gravity field of one body acting on another body by using a clever arrangement of masses. The theoretical possibility of antigravity also appears in quantum gravity theories, cosmological vacuum or dark energy, and quantum field theory. Other types of gravity control include the production of artificial gravity via using ultrahigh-intensity electric or magnetic fields to tailor certain spacetime geometries; the production and use of gravitational waves for rocket propulsion; antigravity (self-lifting) forces induced by the Casimir Effect or by nonretarded quantum interatomic dispersion forces in a background gravitational field; and speculative quantum unified field theories which predict unusual new antigravity forces. The reader should bear in mind that many of these concepts are nowhere near having any form of practicable engineering implementation.
Stay tuned for more info to come…