In our continuing exploration of Sci-Fi Propulsion Systems we continue with solid fuel chemical rocket engines. They were invented about a thousand years ago in China. They were the first engines created by man and have been used widely ever since. As a kid, I built a few model rockets using solid fuel chemical rocket engines and launched them. The C-130 Hercules aircraft uses solid fuel chemical rocket boosters to get heavy loads off the ground on a short runway. And, of course, the Space Shuttle program used solid fuel SRBs to help lift the shuttle into space. Solid fuel chemical rockets are also used in weapons systems such as missiles and torpedoes.
The Advantages & Disadvantages of Solid Fuel Chemical Rocket Propulsion Systems
Solid fuel chemical rocket propulsion systems have the advantage of being relatively cheap to make, simple, and safe (as long as the seals hold). Their disadvantages include the fact that once lit, you cannot shut the down. If they go out on their own they cannot be re-lit, and a pilot cannot throttle up or down. However, they can shape the fuel to provide more thrust early in the burn then taper off. Still, a pilot has no control over the thrust.
Still, solid fuel chemical rocket boosters can give a large, heavy ship a boost out of an orbital position toward its destination. They then discard the boosters or, if feasible they can recover them for reuse.
How Solid Fuel Chemical Rocket Propulsion Systems Work
Basically, you set things on fire explosively, direct the explosion away from where you want to go, and conservation of momentum does the rest. Why conservation of momentum? In the greater scheme of the universe, you must conserve momentum. You cannot create it spontaneously and you cannot destroy it. It’s one of those immutable laws. So, the only way to move is by exchanging momentum with something else.
In a frictionless environment such as space, throwing something as small as an apple would propel you backwards noticeably. This is what most fuels do in essence. They throw something backwards as hard as they can so that they can go forward.
In a solid fuel chemical rocket, engineers mix the propellants together and pack them into a solid cylinder. Under normal temperature conditions, the propellants do not burn but they will burn when exposed to a source of heat provided by an igniter. Once the burning starts, it proceeds until there is no propellant. With a liquid rocket, you can stop the thrust by turning off the flow of propellants but with a solid rocket, you have to destroy the casing to stop the engine. Liquid rockets tend to be heavier and more complex because of the pumps and storage tanks. They load the propellants into the rocket just before launch. A solid rocket is much easier to handle and can sit for years before firing.
Best Mixture to use in Solid Fuel Chemical Rocket Propulsion Systems?
Oxygen and hydrogen are used as propellants because they give off the most energy (isp – Specific Impulse) of any practical combination of chemicals.
Specific Impulse is one of the two key methods of measuring the performance of a rocket system (the other being mass ratio). Understanding Specific Impulse is one of the most important things to understanding orbital rockets.
Just like a measure of the efficiency of a car is MPH, rockets have Specific Impulse, measured in seconds.
Specific Impulse is the number of seconds that one unit weight of propellant will produce one unit force of thrust.
Table of effectiveness of different fuels:
The LOX/H2 mixture will move one unit of mass for the longest amount of time.
Hey, don’t forget to share this post. I’d really appreciate it! Thanks!