Tractor beams are a staple of science fiction space adventures, but I never liked them. They were all too random, with no real science behind them. They were just a lazy prop—a bit of fantasy thrown in to help with the story.
A long time ago, I invented the tractor beam technology I would use. Yes, as a future development, the physics was never explained, but the rules of operation were rigid.
The beam was always double-ended, you could never have a single tractor beam lancing out into space to grab something, there always had to be a beam in the opposite direction as well. The “polarity” of the beams had to match. Both could pull, a tractor beam, or both could push, a pressor beam. And most importantly, momentum is conserved.
You couldn’t pull on a rock in space in one direction and dump the back beam out into empty space. Since momentum is conserved, the back beam would have no effect since there was no mass in its volume so the front beam would have no effect either even when it reached the rock. However, if you had the mass of a planet in the back beam and a rock in the front beam, because Mass X Acceleration = Mass X Acceleration, nearly all of the energy would go into the rock, since the pass of the planet was so overwhelmingly larger.
Beams could be focused with magnetic fields. They could be made narrow like a laser beam or spread out like a floodlight.
The energy for a beam came from a power cell which was just a storage cell where conflicting high energy beams were confined. All operations of the tractor beams conserved, like the operation of a spring. You could put energy into a spring by compressing it, and then that energy was released when the spring returned to normal.
With those basics, a much more elaborate technology developed.
You can charge the power cell by having physical mass overwhelm the force of the beam. Aim the fore beam into the wind and the back beam into the rocks behind you. If the pressor beam is stronger than the wind, moving the air backward, then you drain power. If the beam is weaker than the wind, you slow it down and the energy of the wind flows into your power cell.
Once you get above the atmosphere, more dramatic charging situations can occur. Put yourself between Mars and Venus as they move in their orbits. Venus travels faster than Mars, so if there is a beam attempting to slow down Venus and speed up Mars, the vast mass of the planets overwhelms the beam and enormous energies can be harvested without making a perceptible dent in the planets’ orbital velocities. Energy from the motions of the planets could run all energy needs of Earth and do so much more as well.
Smaller asteroids and moons could be moved, assuming beams and power cells powerful enough to contain those energies.
Space ships no longer needed rockets. Aim the forward beam at the planet of destination and spread the back beam to include part of the hull of the ship and turn on a tractor beam. All of the acceleration goes into the ship. Tens, hundreds of gravities of acceleration was possible, although a counteracting bubble of forces would need to be maintained to keep the pilot from being squashed.
Lifting from Earth’s atmosphere is a harder task. The beam propagates at the speed of light. Almost immediately, the back beam would encompass the mass of the planet and none of the acceleration would go to the ship.
Switching the beam on and off rapidly was the answer. Pulse the tractor beam for a few microseconds and grab the air above, dragging it down, lifting the ship, wait a fraction of a second and repeat. An external, pulsing blast of air goes down as the ship goes up. Repeat until you clear the atmosphere and can push against the atmosphere and planet below you. They coined the name “cirrance” for the process.
Rapid switching in the nanosecond range of tractor beams located below you could give you the illusion of gravity while in space, called “floor gravity”.
With the unlimited energy available from harvesting the planets motions, ships could travel the solar system with reasonable travel times. Asteroids could be relocated. A whole space-based civilization could grow.
And planets could be terraformed.
The core Tractor/Pressor technology was never invented in the Project Saga storyline, only inherited. The Cerik that attempted to invade Earth in Star Time had ships that used TP engines, and there was a crash. Decades later during In the Time of Green Blimps, one of the engines was salvaged and reverse engineered. After that continual refinement of the basic technology created a wide range of devices from tiny floor gravity units to behemoths that were used to move moons. The basic story of the development of the space-based civilization is detailed in a number of short stories combined into a teaching narrative Captain’s Memories.
Several times in the saga, a technically adept character will confront the reality that TP technology and the starship drives are incompatible with physics as we know it. But, as long as the devices follow their own rules, the engineer can use them.
As the author, I could appeal to new physics. New things are being discovered all the time. Instead, in the final book of the saga, Children of Earth Part Three: Demon and the Saint, it is revealed the core science of those impossible technologies came another universe with its own physical rules.