Monopropellant rocket: Difference between revisions

The most commonly{{citation needed|date=January 2011}} used monopropellant is [[hydrazine]] (N₂H₄), a chemical which is a strong [[reducing agent]]. The most common catalyst is granular alumina coated with [[iridium]] (e.g. S-405 or KC 12 GA). There is no igniter with hydrazine. Shell 405 is a spontaneous catalyst, that is, hydrazine decomposes on contact with the catalyst. The decomposition is highly exothermic and produces an 1800 °F (1000 °C) gas that is a mixture of nitrogen, hydrogen and ammonia.{{Citation needed|date=February 2008}}

Another monopropellant is [[hydrogen peroxide]], which, when purified to 90% or higher concentration, is self-decomposing at high temperatures or when a [[catalyst]] is present.{{Citation needed|date=February 2008}}

Most{{Citation needed|date=January 2011}} chemical-reaction monopropellant rocket systems consist of a fuel tank, usually a [[titanium]] or [[aluminium]] sphere, with an ethylene-propylene rubber bladder or a surface tension propellant management device filled with the fuel. The tank is then pressurized with [[helium]] or [[nitrogen]], which pushes the fuel out to the motors. A pipe leads from the tank to a [[poppet valve]], and then to the decomposition chamber of the rocket motor. Typically, a satellite will have not just one motor, but two to twelve, each with its own valve.{{Citation needed|date=February 2008}}

The [[attitude control]] rocket motors for satellites and space probes are often very small, an inch or so in diameter, and mounted in clusters that point in four directions (within a plane).{{Citation needed|date=February 2008}}

The rocket is fired when the [[computer]] sends [[direct current]] through a small [[electromagnet]] that opens the [[poppet valve]]. The firing is often very brief, a few thousandths of a second, and - if operated in air - would sound like a pebble thrown against a metal trash can; if on for long, it would make a piercing hiss.{{Citation needed|date=February 2008}}

Chemical-reaction monopropellants are not as efficient as some other propulsion technologies. Engineers choose monopropellant systems when the need for simplicity and reliability outweigh the need for high delivered impulse. If the propulsion system must produce large amounts of thrust, or have a high [[specific impulse]], as on the main motor of an interplanetary spacecraft, other technologies are used.{{Citation needed|date=February 2008}}