A very curious point comes up in the discussion of interplanetary traveling, that is of traveling through the almost complete vacuum of space. This is the power which would be required to propel a space ship, as it were, through space, when away from and out of the atmosphere of the earth. High resistance would be encountered in getting away from the earth due to the air. As long as the space ship, as we may call it, would be in the lower atmosphere of the earth at 10 or IS pounds pressure to the square inch, a great resistance to its motion and to its acceleration would be imposed by the air.
The overcoming of this resistance is the principal work of the airplane’s or dirigible’s engines. But if the ship, started vertically, or approximately so, from the surface of the earth, twenty miles of travel would get it rid of a very great part of the earth’s atmosphere, and ten or fifteen miles more would virtually bring it into the vacuum of outer space. As soon as there would be no air to oppose its motion, very little power— hardly any, in fact—would be required to drive it ahead, without regard to its speed, provided this were constant. Acceleration and its rate would be resisted only by the mass of the body to be accelerated. This resistance is due to what is called “inertia.” Inertia, if we look up its etymological origin, may be translated as the “laziness of matter,” for even in real life, especially in humanity, laziness is sometimes the deadest kind of resistance. The logical way to treat the subject would be to start our vehicle at a reasonably low, slightly accelerating velocity and to impose the real vigorous acceleration only when the vacuum of outer space would be reached and there was no air to oppose its motion, and to reach this place need not take but a few minutes. Here is the place where the so-called “ratiocination” of the Goddard rocket comes in.
Out of the earth’s atmosphere, and with practically nothing to contend with but the inertia of the mass of the object being propelled—and this only when accelerating—it would be found on calculation that an astonishingly small power would be required to accelerate and virtually no power to keep in motion a body of any mass in space. In the physical sense, mass is a definite factor, and weight may be expressed as an accident. The mass of a body is a real thing; it is 1/32 part, approximately, of its weight. If the body were taken out into space far away from the earth, it would have no weight, but its mass would be unchanged. Mass divided by 2 and multiplied by the square of the velocity in feet per second gives us its inertia, its resistance to a cessation of motion. To impart a velocity of 100 feet per second to a three-ton object in space would require the exertion of about 1,000,000 foot-pounds.