In the nine hundred years since folk dreamed about traveling to other worlds, all kinds of fancy scientific inventions have played their part in making that happen. If you had to pick just one that was most important, it would be the grand unification of the theories of gravity and electromagnetism. This breakthrough led to a relatively cheap means of controlling gravitic attraction and inertia that changed the old notions of space travel and propulsion. Previously only elite astronauts could fly into the black. Now ordinary folk take such trips every day. The math behind all this will surely hurt your head, so we present the short version—the three techniques that cover most all of the basics:
Screening reduces the pull of one object (usually a planet or moon) on another (a spaceship, hovercraft, or maybe a chandelier) and essentially the other way around as well. This allows heavier- than-air vehicles to float without the need for wings and rotors and such. Putting up a screening field takes time and energy, but once the field is going, it doesn’t take much energy to keep it that way. Since aircraft no longer have to fight gravity every moment, and they can take advantage of the almost total lack of friction when flying, aircraft are now practical for all sorts of jobs—from freight handling to rubbernecking. Spacecraft can save their fuel for getting up to orbital velocity.
Note that screening by itself doesn’t change the inertia—the resistance to motion—that heavy objects have, else ships would be blowing away in the least little breeze. Screening does put every object within the field in what amounts to zero gravity, which would be awfully inconvenient for ladies in them fancy hooped skirts, if it weren’t for artificial gravity, which is next. Artificial gravity works the other way, pretending to be a planet-sized mass and pulling on everything in its range.
Artificial gravity provides nearly the same effect as normal gravity inside a screening field and also on ships in free fall. Although artificial gravity can’t actually change the forces of ordinary acceleration, careful handling of the artificial g-field can cancel out most of the tossing caused by movement and—so long as the pilot doesn’t get too crazy—make for a smoother ride. Artificial gravity has also been used on a grand scale in the terraforming of small worlds and moonlets, allowing them to keep a breathable atmosphere despite how dinky they are.
One last benefit of g-fields has to do with fusion, which we’ll get into in a bit under the Power heading.
All this was a big improvement over brute-force rocketry and early space flight. Sailing to the nearest planets would have still taken months if it weren’t for the third technique: inertia reduction. Artificial g-fields and g-screening wouldn’t normally affect the inertia of a ship, but setting them against one another in a particular manner made it possible to drop the ship’s resistance to motion in a specific direction to next to nothing. Spaceships designed to take advantage of this trick have gained greatly in speed and efficiency, though there are some limitations (which we’ll discuss under Propulsion).
Even though screening, artificial gravity, and inertian reduction are three distinct effects, most folks just call the whole gorram thing a grav drive.