Rockets have been made for more than 1,000 years, and represent not only some of man’s oldest technology, but some of man’s most highly-developed technology. From the simplest bottle rockets to our modern rockets, they all rely on one basic principle—Newton’s Third Law of Motion: To every action there is an equal and opposite reaction.
In the rocket motor, the “action” is the hot gases rushing out of the nozzle of the motor at very high velocity, which is caused by the burning of fuel inside the motor. The “reaction” is the force generated on the front wall of the combustion chamber created by the exit of the hot gases from the nozzle.
Some rockets, like the model rockets you might build, and fireworks, use solid propellant. They are light, powerful, and reliable, but once ignited, they burn at a high rate until their fuel is exhausted. Most solid propellant rockets have a hollow core where ignition takes place. Probably the most notable example of a solid propellant rocket are the twin solid propellant boosters used to assist the Space Shuttle on launch.
Most large rockets used for space exploration use liquid fuel. In a liquid-fueled rocket, two types of liquid—fuel and oxidizer—are injected at high pressure into the combustion chamber, where they combine and ignite, generating very hot gases, which exit through the nozzle at very high speeds to provide the force and thrust. While the process might sound simple, large liquid-fuel rockets represent some of the most complex technology developed by humans. The many challenges that must be met to achieve a modern space launch are truly daunting and bear great testimony to the capabilities of our scientific community.
Most large space boosters use cryogenic liquid fuels, often liquid oxygen, as the oxidizer and liquid hydrogen as the fuel. The Space Shuttle’s main engines and the Saturn V are examples. Cryogenic fuels are gases at normal temperature and must be maintained at very low temperatures to remain in a liquid state. Most smaller space vehicles, however, use hypergolic fuels, which are liquid at normal temperatures and ignite spontaneously when mixed together. Since they have simpler handling requirements and require no external source of ignition, they are preferred for small, light space vehicles, which are used to explore other planets.
But whatever type of fuel or design, all rockets still rely on the same laws of motion.
Roy Reed is a board member for the Santa Maria Valley Discovery Museum at 705 S. McClelland in Santa Maria. Discovery Corner is a weekly column in the Sun, highlighting events, science activities, and more. Send comments to discoverycorner@santamariasun.com.
This article appears in May 19-26, 2011.