Liquid Fuel Rockets
Liquid Fuel Rockets
On the cold day of March 16, 1926, Dr. Robert H. Goddard made history in Auburn, Massachusetts. His liquid-fuel rocket named "Nell", powered by gasoline and liquid oxygen, rose from its launch frame into the winter sky. The little rocket reached just 41 feet in a flight that lasted only 2.5 seconds before landing in a cabbage field.
Robert Goddard with His Liquid Fuel Rocket
By modern standards, Goddard’s achievement seems very modest. However, he had achieved a major breakthrough, launching the first liquid-fuel rocket in history. Although Goddard had not originated the idea (that honor belongs to Russian mathematician Konstantin Tsiolkovsky), he was the first one to make it work.
Since that pioneering flight, the liquid fuel rocket has advanced substantially. These rockets now launch payloads weighing many tons into Earth orbit and on toward the moon, Mars and other destinations. They have lofted astronauts to the International Space Station and landed men on the moon.
Despite all the changes over the years, the basic design of a liquid-fuel rocket remains the same. There are three types of liquid rockets: monopropellants, which use a single type of propellant; bipropellants, which use two types of propellants (a fuel and oxidizer); and tri-propellants, which use three types of propellants.
Many different combinations of fuel have been used since Goddard flew his first rocket. Common fuel combinations include:
|Fuels and Oxidizers||Vehicles|
|liquid oxygen (LOX) and gasoline||Goddard's rockets|
|liquid oxygen (LOX) and alcohol (ethanol, C2H5OH)||Redstone (USA); V-2 (Germany)|
|unsymmetric dimethylhydrazine (UDMH) and dinitrogen tetroxide (N2O2)||Cyclone 4 (Ukraine); Proton (Soviet Union/Russia)|
|liquid oxygen (LOX) and kerosene (or RP-1)||Atlas, Delta, Saturn I, Saturn IB, Saturn V, Titan I (USA); R-7 Semyorka, Soyuz (Soviet Union/Russia); Zenit (Soviet Union/Ukraine)|
|liquid oxygen (LOX) and liquid hydrogen (LH2, H2)||Centaur, Delta IV, Saturn V, Saturn IB, Saturn I, Space Shuttle (USA); Ariane 5 (Europe); H-II, H-IIA, H-IIB (Japan)|
|monomethylhydrazine (MMH, (CH3)HN2H2) and dinitrogen tetroxide||Space Shuttle orbital maneuvering system engines and reaction control system thrusters (USA)|
Liquid rockets have several advantages over solid-fuel boosters. They are usually more powerful; the low density of liquid fuel allows for lightweight fuel tanks, which saves weight and boosts the rocket’s payload capacity; and the propellants can be kept under low pressure.
Liquid rockets can be throttled in flight, shutdown and restarted, making them ideal for a variety of space missions. By contrast, solid-fuel rockets must burn once they start and shut down only when they are completely burned out. Liquid-fuel engines can be test fired ahead of time and reused after a flight, unlike solids.
Liquid fuel rockets have a number of disadvantages, however. They burn at high temperatures and require high-speed moving parts. Loss of proper pressurization of thin-walled propellant tanks can cause a catastrophic failure. If propellants such as hydrogen leak, this can result in an explosion. Turbo-pumps are complex and are subject to several types of failures that can result in the loss of a vehicle.
Despite these risks, liquid-fuel rockets remain the most commonly used booster for launching payloads into space because of their high performance and reliability.