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Bloodhound


On the trail of bloodho


Development and testing of the hybrid rocket by Daniel Jubb.


The hybrid rocket for Bloodhound SSC will be the largest hybrid rocket ever made in the UK. In order to propel Bloodhound SSC to 1000 mph, it will provide an average thrust of 111 kN (25,000 lbs) for 20 seconds. The peak thrust will be 122 kN (27,500 lbs). The development of such a large rocket engine is an enormous technical challenge and it was decided that most of the development work would need to be conducted on a smaller research chamber. The 15.2 cm (6-inch) diameter chamber, has proved an excellent development tool. Over the course of the 11 firings conducted to date, it has proved invaluable in the refinement of the catalyst pack, fuel grain and thermal insulation for the full size hybrid chamber.


A rocket is basically an engine which carries both a fuel and oxidiser (it does not require any oxygen from the air). In the early stages of


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the project we looked at the three main types of rocket: solid, liquid and hybrid propellant. Solid propellant rockets are simple and reliable, the fuel is usually a combination of a synthetic rubber binder and a metal powder. The oxidiser is generally a crystalline solid (such as Ammonium Perchlorate), the fuel and oxidiser are premixed into a propellant grain which is contained in a motor case.


Solids offer good performance, however once ignited they cannot easily be stopped, making them unsuitable for a land speed record car, which may need to slow down at any point during the run. Liquid propellant rockets offer high performance, although they are very complex and the flow rates and delivery pressures of the fuel and oxidiser must be controlled precisely to maintain the correct mixture ratio. Liquid fuels include kerosene, liquid hydrogen and alcohol. The main liquid


oxidisers are liquid oxygen, nitric acid, nitrogen tetroxide and High Test Peroxide (HTP). Hybrid propellant systems use a solid fuel and a liquid oxidiser. The fuel is contained within the combustion chamber and the liquid oxidiser is injected at the top of the chamber. Therefore a hybrid can be easily shutdown by turning off the supply of liquid oxidiser.


Hybrids use the same oxidisers as liquid propellant systems. Fuels can include synthetic rubbers and plastics (such as PVC). It was decided that a hybrid was the most suitable choice for Bloodhound SSC. The next question was the choice of propellants, Hydroxyl- Terminated Polybutadiene (HTPB) a synthetic rubber was selected as the primary fuel. All liquid oxidisers are hazardous, although the hazards take different forms. HTP was selected as the oxidiser; HTP is concentrated hydrogen peroxide H2O2 (in this case 86%, the balance


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