Page 39 - Curriculum Visions Dynamic Book

Propulsion in space
Fuels burn because they have a supply of oxygen. In space there is no oxygen, so this must be provided. All spacecraft – rockets, space shuttles, etc. – must have their own on-board supply of oxygen. This can be supplied as liquid oxygen or as an oxidising chemical.
The strongest of all common acids is called perchloric acid. If even a small amount of perchloric acid gets into contact with any organic matter, the reaction is so swift that it can cause an explosion. This oxidation potential can be used
to great advantage under controlled
conditions. In the booster rockets
of the space shuttle, ammonium
perchlorate and aluminium powder are
packed together. The fuel (aluminium
powder) thus has its own oxygen
supply as ammonium perchlorate
As it burns, the mixture throws
out clouds of white aluminium oxide powder, hydrochloric acid gas, nitrogen oxide gas and water vapour. It is the rapid expansion of these gases that provides the thrust for the space shuttle and the white trail that you can see.
combustion: the special case of oxidisation of a substance where a considerable amount of heat and usually light are given out. Combustion is often referred to as “burning”.
fuel: a concentrated form of chemical energy. The main sources of fuels (called fossil fuels because they were formed by geological processes) are coal, crude oil and natural gas. Products include methane, propane and gasoline. The fuel for stars and space vehicles is hydrogen.
welding: fusing two pieces of metal together using heat.
 A space shuttle taking off. The brown tank underneath the space shuttle contains liquid oxygen and hydrogen fuel.
 Oxyacetylene welding in progress.
Oxyacetylene cutting and welding
Liquid oxygen is used in bottled form for oxyacetylene cutting and welding.
In this process, the acetylene fuel (kept liquefied in a cylinder) is fed into a nozzle, where it combines with oxygen supplied from a separate cylinder. When this mixture is ignited the reaction releases
a large amount of heat, while producing carbon dioxide gas and water vapour.
Oxyacetylene torches can reach temperatures of over 3300°C. This flame is so hot it can melt metal, which is why it is used in welding.
By changing the nature of the oxygen and acetylene head, the torch can be made to cut metal. In this case a jet of oxygen is introduced into the centre of the acetylene flame. This oxidizes the white-hot metal, leaving a narrow, clean- edged cut.
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