Fluidic Microsystems for Micropropulsion Applications in Space

Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission. Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work. Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified. A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve. The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements. For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine. A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar. The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility

Fluidic Microsystems for Micropropulsion Applications in Space

Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission. Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work. Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified. A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve. The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements. For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine. A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar. The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility

Experimental Studies of Sealing Mechanism of a Dismountable Microsystem‑to‑Macropart Fluidic Connector for High Pressure and a Wide Range of Temperature

As fluidic microelectromechanical devices are developing and often attached to, or embedded in, large, complex and expensive systems, the issues of modularity, maintenance and subsystem replacement arise. In this work, a robust silicon connector suitable for high-pressure applications – likely with harsh fluids – in the temperature range of +100 to –100°C is demonstrated and tested together with a stainless steel nipple representing a simple and typical macropart. With a micromachined circular membrane equipped with a 5 μm high ridge, this connector is able to maintain a leak rate below 2.0´10-8 scc/s of gaseous helium with a pressure of up to 9.7 bar. Degradation of the sealing performance on reassembly is associated with the indentation of the ridge. However, the ridge makes the sealing interface less sensitive to particles in comparison with a flat reference. Most evaluation is made through so called heat-until-leak tests conducted to determine the maximum working temperature and the sealing mechanism of the connector. A couple of these are followed by cryogenic testing. The effect of thermal mismatch of the components is discussed and utilized as an early warning mechanism

Thermally regulated valve for minute flows

In this work, a gas valve using a microstructured silicon valve lid and a stainless steel valve seat clamped axially together in an aluminum cylinder is investigated. The difference in coefficient of thermal expansion of these components makes the valve open and close on a temperature change. A simple model accounting for elastic deformation of the system’s components is proposed to facilitate design of the valve. By means of a helium leak detector, a typical increase in flow rate from 1.0×10−8 to 1.0×10−4 sccs gaseous helium under a pressure of up to 10 bars was observed upon the increase of temperature from 12 to around 98 °C, after a single breaking-in. Plastic deformation of the valve seat as a consequence of an imprint of the microstructured valve lid and contaminating particles was studied. Microscopy confirmed a tolerance for particles of up to a few micrometers in diameter. Larger particles were found to be a possible cause of failure

A solder sealing method for paraffin-filled microcavities

Demonstrated and investigated here is a method to seal microfluidic systems by soldering. As a particularly difficult case of growing importance, the sealing of openings contaminated with paraffin wax was studied. Solder paste, screen printed on a metallized silicon, substrate was melted locally through application of 6.5 to 10 V to a 5 Ω copper film resistor for a few seconds and found able to drive an intermediate layer of paraffin away and seal a 0.2 mm diameter circular via by wetting to a surrounding copper pad. Although verified to be robust, the process did result in failing seals on excessive heating because of consumption of the pads. Correctly performed, the technique provided a seal at least withstanding a pressure of 8 bar for 8 h at 85ºC

Numerical modeling and verification of gas flow through a network of crossed narrow v-grooves

The gas flow through a network of crossing thin micro-machined channels has been successfully modeled and simulated. The crossings are formed by two sets of v-grooves that intersect as two silicon wafers are bonded together. The gas is distributed from inlets via a manifold of channels to the narrow v-grooves. The narrow v-grooves could work as a particle filter. The fluidic model is derived from the Navier–Stokes equation and assumes laminar isothermal flow and incorporates small Knudsen number corrections and Poiseuille number calculations. The simulations use the finite element method. Several elements of the full crossing network model are treated separately before lumping them together: the straight v-grooves, a single crossing in an infinite set and a set of exactly four crossings along the flow path. The introduction of a crossing effectively corresponds to a virtual reduction of the length of the flow path, thereby defining a new effective length. The first and last crossings of each flow path together contribute to a pressure drop equal to that from three ordinary crossings. The derived full network model has been compared to previous experimental results on several differently shaped crossed v-groove networks. Within the experimental errors, the model corresponds to the mass flow and pressure drop measurements. The main error source is the uncertainty in v-groove width which has a profound impact on the fluidic behavior

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In this work, a gas valve using a microstructured silicon valve lid and a stainless steel valve seat clamped axially together in an aluminum cylinder is investigated. The difference in coefficient of thermal expansion of these components makes the valve open and close on a temperature change. A simple model accounting for elastic deformation of the system’s components is proposed to facilitate design of the valve. By means of a helium leak detector, a typical increase in flow rate from 1.0×10−8 to 1.0×10−4 sccs gaseous helium under a pressure of up to 10 bars was observed upon the increase of temperature from 12 to around 98 °C, after a single breaking-in. Plastic deformation of the valve seat as a consequence of an imprint of the microstructured valve lid and contaminating particles was studied. Microscopy confirmed a tolerance for particles of up to a few micrometers in diameter. Larger particles were found to be a possible cause of failure

MEMS Micropropulsion Components for Small Spacecraft

This paper presents a number of MEMS-based micropropulsion components for small spacecraft. First a description of four components, all integral parts of the cold gas micropropulsion system custom designed for the Prisma satellites (launched June 2010). One of the most complex miniaturised micropropulsion components on board Prisma is the MEMS thruster chip, comprising four microthrusters integrated in a six-silicon-wafer package weighing only 4 grams. Proportional MEMS thruster valves and internal gas heaters are key integral parts of the thruster chip, providing μN-to-mN thrust in four orthogonal directions. Other MEMS components on Prisma are: a MEMS isolation valve, a MEMS pressure relief valve, and a MEMS pressure sensor. Hereafter, further developments of the MEMS components are presented, e.g. implementation of closed-loop thrust control on the MEMS thruster chip and proportional valves for ion engines to regulate xenon in the 5-50 μg/s regime with a 0.2 μg/s resolution. Finally, a concept of a completely miniaturised propulsion system intended for CubeSat applications is shown. All components are good examples of how extreme mass savings can be achieved by using MEMS technology, and by integrating several components and functionalities into one common chip or housing, which is of special interest for small spacecraft missions