Rocket thrusters

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

Propulsion System. The propulsion system performs occasional maneuvers required to keep Earthorbiting satellites on station or interplanetary probes on course. The propulsion system consists of rocket thrusters, propellant, pumps, valves, and pressure vessels. Attitude control thrusters control the rotational dynamics of the spacecraft. Course correction thrusters change the speed or direction of motion of the spacecraft. The propellant must be storable for long periods of time under the harsh conditions of space. Special pressurization techniques are necessary to move liquid propellants from tanks to thrusters in zero gravity. The spacecraft must carry enough propellant for the planned mission lifetime plus a reserve necessary for deorbit at end of life. 

Currently, there is a good deal of interest in HfC for rocket thrusters (Patterson, 1996). Shimada et al. (1997) have examined the oxidation of HfC from 600 to 900 °C. There are many similarities to ZrC oxidation. A two zone structure is formed where the inner layer forms with diffusion-con-trolled kinetics and the outer layer forms with interface-controlled kinetics. Unlike ZrC oxidation, only the monoclinic form of the product oxide (Hf02) is observed. Carbon is observed in both layers (Shimada, 1999). At temperatures of 1400-2100 °C Bargeron et al. (1993) also observed a multi-layer product structure. In this case the outer layer contained no carbon. 

Iridium Coating for Spacecraft Rocket Nozzles. The coating of rocket nozzles with iridium is a good example of the ability of CVD to provide a complete composite material, in this case a structural refractory shell substrate coated with a corrosion- and oxidation-resistant component. The device is a thruster rocket nozzle for a satellite. The rocket uses a liquid propellant which is a mixture of nitrogen tetroxide and monomethyl hydrazine. 

The use of N2H4 as a hypergolic propellant fuel for rocket propulsion is discussed in detail in this Vol under Hypergolic Propellants. It has also been used extensively as a monopropellant fuel or in combination with hydrazine nitrate and/or water as a thruster for maneuvering space vehicles (Ref 31)... 

The use of N2H<, as a hypergolic rocket fuel is described under the topic Hypergolic Propellants in this Vol. Another major research effort has seen the development of hydrazine thruster rockets based upon the catalytic de-... 

Thrusters are rockets for maneuvering and controlling the attitude of space vehicles. The usual monopropellant for thrusters is catalytically decomposed Hydrazine. The usual catalysts are iridium, rhodium or ruthenium and their mixts. For a review of Hydrazine thrusters see Refs 33, 34 35. Russi (Ref 34) emphasizes that, in spite of many studies and the general acceptance and apparent success of hydrazine thrusters, new rocket motor design is still largely empirical. A biproplnt consisting of Hydrazine mixed with Hydrazine Nitrate has also been tried in thrusters but is no longer popular... 

Applications. To date, the liquid propellant systems used in chemical propulsion range from a small trajectory control thruster with only 0.2 lbf (0.89 N) thrust for orbital station-keeping to large booster rocket engines with over l. 0 million lbf (4.44 MN) thrust. Bipropellant propulsion systems are the most extensively used type today for... 

Moreover, there is a current need of miniaturized propulsion system for widening the capabilities of low cost micro-satellites. Recently, the development of a turbo-pump fed miniature rocket engine has been proposed as a new propulsion system for micro-satellites (10 to 100 kg) [6] the bipropellant tlmister uses 70 wt.-% H2O2 as oxidizer and ethanol as fuel. The engine displays four sub-components (i) two propellant micro-pumps, (ii) a HP decomposition chamber, (iii) a turbine coupled to an electric power generator and driven by the hot gas released from HP decomposition, and (iv) a thruster for the combustion reaction. 

Thrusters can be used in either continuous or pulsed operation, according to the application. Miniature rocket launchers and micro air vehicles require a continuous thrust and are best served by a unique thruster or engine with a continuous feed of propellant. Alternatively, digital micropropulsion refers to an array of single-use thrusters that provide a small impulse (short burst of thrust) to accurately orient a small spacecraft or correct a vehicle s trajectory. 

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