I'm becoming sad as I see post after post treating it as "obvious" that it requires continuous power input to hover. It really, really, truly, does not. Energy is required to rise in a potential field (like a gravity well), and energy is dissipated when you fall in a potential field. If you are stationary, your potential energy is constant, and thus no energy is needed to maintain your position.

This is entirely distinct from the question of force. An object in a potential field experiences a force in the direction of lower potential, and if nothing counters that force, it accelerates in that direction. For a hovering helicopter, the counterforce is provided by pushing a lot of air downward. For my phone right now, which is "hovering" a meter above the floor and ~6000 km above the center of mass of the Earth, the counterforce is provided by the surface of the table it's resting on. One requires a lot of continuous power input; the other requires no power input at all.

If you could somehow (handwave, handwave) shield an object from the force induced by a potential field, you could hover in that field at the energy cost of whatever it takes to maintain that shield. Full stop.

On Fri, Aug 25, 2017 at 10:04 AM, David Shaw <xxxxxx@gmail.com> wrote:

On 25 Aug 2017 15:49, "David Shaw" <xxxxxx@gmail.com> wrote:
I have a vague memory of TNE stating that it neutralised *almost* all gravity, enough so that a 1g drive was sufficient to lift off from any surface and that's the way I play it. Unfortunately, my TNE books are not readily available, so I can't easily check.

Found it - FFS page 75

"Contra-Grav
Many spacecraft have contra-grav (CG) lifters as fuel-efficient means of landing and taking off from a planet surface, and CG lifters are also used on grav vehicles. CG lifters do not provide thrust and so cannot physically lift a craft or vehicle. Instead, they neutralize most of the gravitational attraction of a world (approximately 99% of gravitational force, beyond which power use becomes prohibitive). This, combined with atmospheric pressure, will provide buoyancy in very dense atmospheres and so allow the craft to float at low altitudes, but usually CG is used only as an adjunct to the ship's thrusters. By neutralizing most of a world's gravitational field, a ship with
only 1G of thrust can still escape the world's gravity well."

David Shaw
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