Bipropellant rocket

F-1 rocket engine (The kind used by the Saturn V.)

A bipropellant rocket is a rocket that uses separate liquid fuel and oxidizer propellants. In contrast, solid rockets require no oxidizer, and hybrid rockets use solid propellants with a liquid or gaseous oxidizer. Bipropellant systems are more efficient than monopropellant systems, but they tend to be more complicated because of the extra hardware components needed to make sure the right amount of fuel gets mixed with the right amount of oxidizer, known as the mixture ratio.

Thousands of combinations of fuels and oxidizers have been tried over the years. Some of the more common and practical ones are:

• liquid oxygen (LOX, O₂) and liquid hydrogen (LH2,H₂) - Space Shuttle main engines, Ariane 5 main stage, Saturn V, Saturn IB, and Saturn I upper stages as well as Centaur rocket stage

• liquid oxygen (LOX) and kerosene or RP-1 - Saturn V, Zenit rocket, R-7 family of Soviet boosters, which includes Soyuz, Delta, Saturn I, and Saturn IB first stages, Titan I and Atlas rockets

• liquid oxygen (LOX) and alcohol (Ethanol, C₂H₅OH) - early liquid fueled rockets, like German (WW2) A-4, aka V-2, and Redstone

• liquid oxygen (LOX) and gasoline - Robert Goddard's first liquid-fuel rocket

• T-Stoff (80% Hydrogen Peroxide, H₂O₂) and C-Stoff (methanol, CH₃OH, and hydrazine hydrate, N₂H₄.n(H₂O) - Walter Werke HWK 109-509 engine used on Messerschmitt Me 163B Komet a rocket fighterplane of (WW2)

• nitric acid (HNO₃) and kerosene - Soviet Scud-A, aka SS-1

• inhibited red fuming nitric acid (IRFNA, HNO₃ + N₂O₄) and unsymmetric dimethyl hydrazine (UDMH, (CH₃)₂N₂H₂) Soviet Scud-B,-C,-D, aka SS-1-c,-d,-e

• nitric acid 73% with dinitrogen tetroxide 27% (=AK27) and kerosene/gasoline mixture - various Russian (USSR) cold-war ballistic missiles, Iran: Shahab-5, North Korea: Taep'o-dong-2

• hydrogen peroxide and kerosene - UK (1970s) Black Arrow, USA Development (or study): BA-3200

• hydrazine (N₂H₄) and red fuming nitric acid - Nike Ajax Antiaircraft Rocket

• Aerozine 50 and dinitrogen tetroxide - Titans 2–4, Apollo lunar module, Apollo service module, interplanatary probes (Such as Voyager 1 and Voyager 2

• Unsymmetric dimethylhydrazine (UDMH) and dinitrogen tetroxide - Proton rocket and various Soviet rockets

• monomethylhydrazine (MMH, (CH₃)HN₂H₂) and dinitrogen tetroxide - Space Shuttle Orbital maneuvering system (OMS) engines

Robert Goddard and his rocket

One of the most efficient mixture, oxygen and hydrogen, suffers from the extremely low temperatures required for storing hydrogen and oxygen as liquids (around 20 K or -253 °C)) and low fuel density (70 kg/m³), necessitating large and heavy tanks. The use of lightweight foam to insulate the cryogenic tanks caused problems for the Space Shuttle Columbia's STS-107 mission.

For storable ICBMs or interplanetary spacecraft, keeping the fuel cool seems to be an unsolvable problem. Because of this, mixtures of hydrazine and its derivatives in combination with nitrogen oxides are generally used for such rockets. Hydrazine has its own disadvantages, being a very caustic and volatile chemical. Consequently, hybrid rockets have recently been the vehicle of choice for low-budget private and academic developments in aerospace technology.

Small scale rocket engines

XCOR Aerospace, a California based company, is developing small scale rocket engines to power small airplanes for suborbital flights. They have tested various combination of propellants including nitrous oxide/propane, nitrous oxide/alcohol, LOX/alcohol, LOX/kerosene with success.

See also

• spacecraft propulsion
• tripropellant rocket
• hypergolic rocket fuels