In our previous discussion here and here, we covered various methods to reach space without the use of rocket propulsion in its entirety. We have covered static and dynamic structures.

Today, in this last part, we will end this topic with a discussion on the method of using “Projectiles” as a launch system for reaching orbit.

Early thoughts: Newton’s Cannonball

Newton’s cannonball is a famous thought experiment in which you fire a cannonball from the top of a high mountain. Had there been no gravity or air resistance, the body would fly away in a straight line away from Earth, in the direction that it was projected.

However, in presence of gravity, it will follow a parabolic path and fall back to earth. The beautiful idea of this is, if the initial velocity is high enough (equal to the orbital velocity of that height), the ball will “keep” falling but never touch the earth’s surface, thereby reaching orbit.

An illustration of Newton's cannonball thought experiment.
An illustration of Newton’s cannonball thought experiment.

So how do we launch the projectile?

With a projectile launcher, a high velocity is provided at, or near, ground level. In order to achieve orbit, the projectile must be given enough extra velocity to punch through the atmosphere, unless it includes an additional propulsion system (such as a rocket).

Importantly, the projectile also requires something that can circularize the orbit. This is a consequence of orbital mechanics — all orbits must pass through the point where the orbital velocity was last changed, eg:- the muzzle of the gun or projectile system.

The different projectile systems are categorized into three: Electromagnetic, Chemical, and Mechanical systems.

Electromagnetic System

Mass Driver

Also called an electromagnetic catapult, it is a proposed method in which a linear motor is used to accelerate and catapult payloads up to high speeds. Here, a very long and horizontally aligned launch track or tunnel is used for accelerating payloads to orbital or suborbital velocities.

The concept is somewhat similar to the concept of maglev trains. Here also, repulsion is used to keep a payload separated from the track or walls. Then it uses a linear motor to accelerate the payload to high speeds. After leaving the launch track, the payload would be at its launch velocity.

A mass driver for lunar launch (artist's conception). Credits: NASA
A mass driver for lunar launch (artist’s conception). Credits: NASA

Star Tram

This is similar to Mass driver in concept. Instead of horizontal rails, the idea here is to launch vehicles directly to space by accelerating them with a mass drive from a mountain peak at an altitude of 3 to 7 kilometers.

StarTram launching a rocket. (Concept). Credits: NASA
StarTram launching a rocket. (Concept). Credits: NASA

Chemical System

Space Gun and Ram Accelerator

A space gun is a proposed method of launching an object into outer space using a large gun, or cannon. Ram accelerator on the other hand utilizes a jet engine propulsion method to accelerate a projectile inside a tube to high speeds.

Mechanical Methods

Slingatron

In a slingatron, projectiles are accelerated along a rigid tube or track that typically has circular or spiral turns, or combinations of these geometries in two or three dimensions.

The entire curved tube is propelled in a small-amplitude circular motion with constant or increasing frequency to accelerate a projectile inside of it; in other words, the entire tube gyrates but does not spin.

It is common practice to use this motion to stir beverages by holding the container still and moving it in tiny horizontal circles, which causes the liquid inside to spin independently of the container.


Join here for informative articles on Rockets and Space, twice a month.


Leave a Reply