Active Structures

Introduction

Active structures rely on constant power input, in addition to the material and mechanical properties of their construction materials (active support). This is in contrast to passive structures, which solely rely on the aforementioned properties (passive support). An example of an active structure is the force of a jet of water holding up a tethered lid of a trashcan in the air, versus the passive structure of a concrete pillar.
Nearly everything, from skyscrapers to houses are passive structures. Low-power active structures are in use now, for things like roof support.

The advantage of active structures is that they can be much more massive than passive structures , enabling structures many kilometers tall without requiring significant tapering. Some proposals for non-rocket launch infrastructure rely on active support, with the advantage of the option for being built by modern, existing materials.

Most known designs of active structures rely on the force of a stream of mass to support them, using an accelerator to drive the mass stream.

Active Support Principles

As gravity is what pulls down objects, active support must counteract gravity. Since it is the acceleration that causes objects to be pulled down, it follows that active support should accelerate in the opposite direction; the acceleration must be equal to gravity to support the structure.

The gravitational acceleration of the planet is given by:

$A_{g}=G(M_{p}/r_{p}^{2})$

• Where $A_{g}$ is the gravitational acceleration.
• Where $G$ is the universal gravitational constant, defined to be 6.6743e11 m³/kg/s².
• Where $M_{p}$ is the mass of the planet.
• Where $r_{p}$ is the radius of the planet.

On Earth, $A_{g}$ equals 9.80665 m/s², a constant known as g.

Mass Streams

Mass streams generally use particle accelerators or similar technology to create the streams. They use a deflector, usually magnetic, to receive the force from the stream and redirect it back towards the ground to create a loop.

The force required to accelerate the active structure is given by Newton’s second law of motion:

$F=MA$

• Where $F$ is the force exerted on the deflector.
• Where $M$ is the mass of the structure.
• Where $A$ is the antigravity acceleration.

This also applies to the mass stream, the cumulative force of the stream must be equal to this force. If the total mass of the mass stream is lower than the mass of the structure, the acceleration for the stream must be higher.

The acceleration required for each particle or pellet of the stream is calculated with:

$A_{s}=F/N_{m}/M_{m}$

• Where $A_{s}$ is the acceleration of the particle.
• Where $N_{m}$ is the amount of particles or pellets in the stream. The amount for particles is given by:

$M_{s}/N_{s}$

• Where $N_{s}$ is the molar mass of the stream material.

• Where Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle M_s} is the mass of the stream.

• Where $M_{m}$ is the mass of the particle or the pellet.