Modular Micro Propulsion System

The miniaturization of space applicable devices by means of MEMS technology is pursued by many research groups. MEMS devices are often designed as stand alone and require individual packaging which often makes them still quite large. Focusing on the integration of several MEMS components has the advantage of reducing size and mass much more. An integrated and miniaturized cold gas propulsion system for micro satellites is presented which consists of a valve, a particle filter, a pressure sensor, a nozzle and a gas tank. By selecting a convenient package first and adjusting the MEMS part to fit the package, costs are reduced and modularity is obtained. The baseline of the system is a glass tube bonded on a silicon disc which contains a valve seat as shown in Figure 1. The valve is normally closed by an embossed membrane which is stacked inside the glass tube. A piezo-disc is glued to the boss of the membrane to actuate the valve. The glass tube is functioning as hermetically sealed package as well as fluidic interconnect with the macro world. The pressure sensor and particle filter are suspended in the glass tube. This integrated system is connected to a pressurized N2 gas tank which is developed by TNO [1]. The tank contains 8 cold gas generators which makes it possible to reduce the working pressure to 3.4bar withoutcompromising on the amount of gas. During the symposium the technical development and results will be presented

Design of a cold gas micro thruster

Keywords: Micro satellites, Micro propulsion, MEMS technologie

System analysis of high speed, long range weapon systems

Many countries are developing technologies for future hypersonic air breathing cruise missiles. These missiles are foreseen to be employed against, amongst others, deeply buried targets. The main technological challenges are related to severe aerodynamic heating and complex physical processes of aerodynamics and combustion at hypersonic flight speed. This paper reports on a study of the flight mechanics of these systems. Engineering methods for both aerodynamics and propulsion were extracted from literature and have been integrated in a so-called system engineering tool which allows for a performance analysis of the complete system. Two baseline configurations have been defined for this performance analysis (an axi-symmetric and waverider type of configuration). The system engineering tool allows for studying design choices (e.g. ramjet or scramjet propulsion) and for studying the effect of subsystem model uncertainties on overall system performance. These studies can be done for a wide range of mission parameters (like cruise flight Mach number, weapon dimensions, etc). The first system analyses that have been performed have yielded insight in the effects of design choices and model uncertainties on system performance. More exhaustive system analyses will help in determining the directions for follow-on research by narrowing down the broad range of possible designs for hypersonic air breathing cruise missiles and by focussing on developing more detailed prediction models for subsystem aspects that influence system performance most. Copyright © 2005 by TNO

Economic Benefits of the Use of Non-Toxic Mono-Propellants for Spacecraft Applications

The European Space Agency and other institutions have identified the use of non-toxic (or "green") propellants as a substantial cost saving opportunity in manufacturing and ground operating of spacecrafts. This paper attempts to identify and quantify this potential by replacing, in the near future, hydrazine, the current state-of-the-art propellant for small-to-medium size spacecrafts, with green mono-propellants. While most existing publications report results of specific propellant formulation development and testing at thruster and component level, this paper intends to quantify the cost reduction potential for satellite manufacturers arising from simplification of hardware and ground operations. The economic benefit potential of the use of non-toxic spacecraft mono-propellants is investigated by focussing on the four main cost driving parameters: · Reliability and safety, · Manufacturing, assembly, integration and test operations, · Launch preparation and support, · Ground support equipment and personal protection. Further, an extensive market analysis is presented where the currently available and investigated propellant formulations are screened and graded against defined selection criteria. Based on this grading a potential future mono-propellant is arrived at. The economic benefit of this specific propellant formulation is then quantified. The potential recurring cost saving for a 10 spacecraft constellation-type program is evaluated being in the order of € 2.5M, a sum which could provide a business case, also when considering one-off non-recurring costs for verification and validation of a propulsion system utilising green propellants. An outlook for the short and medium term is presented. It is argued that with reasonable expenses for hardware development and validation a demonstrator for the replacement of hydrazine may be feasible in the near future. Finally a "road map" for the long term is shown, where propellant formulations with higher performance characteristics than hydrazine may increase the utilization envelope for mono-propellant systems into the lower domain of bi-propellant propulsion. This could lead to a real "quantum-leap" in the efforts to pursue significantly lower satellite costs. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved

Hybrid simulations of rarefied supersonic gas flows in micro-nozzles

We show that accurate predictions of gas flow and pressure in axisymmetric micro-thruster nozzles with throat diameters in the µm range, and thrusts in the µN range, cannot be performed using continuum based Computational Fluid Dynamics with slip flow boundary conditions, but can be performed by applying a static, one-way, state-based coupling between a CFD solver applied upstream from a properly chosen cross sectional (perpendicular to the nozzle axis) interface, and a Direct Simulation Monte Carlo solver applied downstream from that interface. These hybrid CFD/DSMC simulations can be performed in 5-25% of the CPU time required for a full DSMC simulation, with an accuracy better than 1-2%. A non-optimal choice of the interface location may increase the errors up to several tens of percents, when the interface is located too far downstream, or increase the CPU time by up to several tens of percents, when the interface is located too far upstream. The proper interface location does not generally coincide with the throat plane, but lies upstream or downstream from the throat, depending on the flow conditions. We provide a quantitative criterion, based on Knudsen numbers as estimated from full CFD simulations of the entire nozzle, to determine the proper interface location a priori. Due to frictional losses and rarefaction effects, the total thrust of micro-nozzles in the µN range is found to be several tens of percents lower than the thrust predicted from one-dimensional isentropic theory. © 2011 Elsevier Ltd

Effects of wavy surface roughness on the performance of micronozzles

Recent trends in small-scale (~1 dm3) satellites motivate the further development of microscale propulsion subsystems. In the present paper, we focus on flow dynamics simulations of conical convergent-divergent micronozzles and on the increased importance of wall effects due to the decrease in the characteristic length of such small systems. The inefficiency associated with viscous losses due to the developing boundary layer and the effect of sinusoidal surface roughness due to the employed microelectromechanical-system fabrication techniques are studied through computational fluid dynamics simulations for nonturbulent, nonrarefied flow conditions. Depending on the specific nature of the surface roughness, the formation and reflection of several weak shocks and, as a consequence, a decreased performance are observed. © 2010 by the American Institute of Aeronautics and Astronautics, Inc

Evaluation of micronozzle performance through DSMC, navier-stokes and coupled dsmc/navier-stokes approaches

Both the particle based Direct Simulation Monte Carlo (DSMC) method and a compressible Navier-Stokes based continuum method are used to investigate the flow inside micronozzles and to predict the performance of such devices. For the Navier-Stokes approach, both slip and no-slip boundary conditions are applied. Moreover, the two methods have been coupled to be used together in a hybrid particle-continuum approach: the continuum domain was then investigated by solving the Navier-Stokes equations with slip wall boundary condition, whereas the region of rarefied regime was studied by DSMC. The section where the domain was split was shown to have a great influence in the prediction of the nozzle performance. © 2009 Springer Berlin Heidelberg

Industrial benefits of applying HNF in monopropellant satellite propulsion

The benefits of advanced HNF monopropellants are discussed. The areas of consideration comprise the operational and performance aspects, the general handling, the benign less-toxic characteristics and the envisaged reduction of manufacturing, test and operational costs. The recently proposed developments and applications of advanced monopropellants for satellite propulsion are reviewed. Besides HNF monopropellants, others will be considered like Ammonium Dinitramide (ADN) and Hydroxyl Ammonium Nitrate (HAN). The evaluation of the parameter matrix justifies the selection of HNF as promising alternative as a less-toxic monopropellant for satellite propulsion. The selection of HNF is mainly based on the fact that HNF offers a higher potential performance growth than other monopropellants. The specific propulsion issues with the application of HNF are presented on both component and system level. The thruster has to cope, among other aspects, with catalyst compatibility and long-term stability. The system components like the feed lines, tanks and others need verification. The GSE however might be simplified significantly. In summary the application of HNF offers a high potential of operational advantages and will justify the required efforts for the introduction and the development of HNF in satellite propulsion