A report proposes monopropellant microthrusters for a new generation of miniature spacecraft with mission lifetimes stretching into years. These thrusters would include micromachined nozzle/chamber assemblies containing microvalves, designed according to emerging concepts of microelectromechanical systems (MEMS). Like some previously designed monopropellant thrusters, these thrusters would generate expanding gases and thereby generate thrust through catalytic dissociation of liquid hydrazine; however, these thrusters would be considerably smaller. Moreover, instead of putting catalytic pellets in chambers according to the previous designs, one would roughen the inner walls of the chambers and coat them with iridium or some other suitable catalyst. The micromachined thruster assemblies would be enclosed within aerogel bodies for thermal insulation. Each thruster would be heated with a small amount of power (< 1 W) to promote vaporization. Flow geometries and the characteristic times of residence and dissociation of hydrazine would be optimized.
This work was done by Philip Moynihan and Carl Guernsey of Caltech for NASA's Jet Propulsion Laboratory. To obtain a copy of the report, "Monopropellant Hydrazine Microthruster," access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Machinery/Automation category,or circle no. 180 on the TSP Order Card in this issue to receive a copy by mail ($5 charge). NPO-20159
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Micromachined Monopropellant Thrusters
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Overview
The document discusses the development of micromachined monopropellant thrusters designed for miniature spacecraft, which are expected to have mission lifetimes extending into years. The thrusters utilize liquid hydrazine as a propellant, which is decomposed in a catalyst chamber to generate thrust. Unlike traditional monopropellant thrusters that use catalyst pellets, this new design incorporates a roughened inner wall of the chamber coated with a suitable catalyst, such as iridium. This innovative approach allows for a significant reduction in size and weight, making the thrusters suitable for microspacecraft.
The report highlights the advantages of using microelectromechanical systems (MEMS) technology, which enables the construction of these thrusters through cost-effective manufacturing processes like micromachining and vapor deposition. The design aims to achieve a specific impulse approximately twice that of gaseous nitrogen, enhancing the efficiency of the propulsion system. The entire assembly is enclosed in aerogel, a lightweight material with excellent thermal properties, which provides thermal insulation and contributes to the overall efficiency of the system.
The need for such miniaturized propulsion systems arises from the increasing demand for smaller spacecraft capable of long-duration missions. These missions often require reliable and predictable thruster performance after extended periods of inactivity, necessitating a propulsion system that minimizes propellant loss due to leakage. The use of liquid propellant, as opposed to pressurized gas, simplifies the sealing requirements and enhances the system's reliability over long mission timelines.
The document also emphasizes the potential for these microthrusters to be integrated into three-axis stabilized platforms for attitude control, addressing the evolving needs of space missions. The development of these thrusters is part of a broader initiative at NASA's Jet Propulsion Laboratory to miniaturize components and sensors while maintaining or improving performance for future missions.
In summary, the report outlines a significant advancement in propulsion technology for miniature spacecraft, focusing on the design, manufacturing, and operational benefits of micromachined monopropellant thrusters. This innovation is expected to play a crucial role in the future of space exploration, particularly for missions requiring long-term stability and efficiency.
