Johan Bejhed

A Hybrid Cold Gas Microthruster System for Spacecraft

A hybrid cold gas microthruster system suitable for low Δv applications on spacecraft have been developed. Microelectromechanical system (MEMS) components together with fine-mechanics form the micr ...

Demonstration of a single use microsystem valve for high gas pressure applications

Demonstrated and characterized here is a single use valve developed for high-pressure applications. Incorporated within the single use valve is a particle filter. The filter serves to remove any particle debris created by the activation process. The valve is solder sealed to be leakage proof. The solder is remelted to obtain activation of the valve. Local heater elements are incorporated on the valve surface together with solder wetting pads. The gas mass flow through the device was evaluated prior to sealing and after activation. The valve was functional at pressures of 100 bar, and opened in less than 10 s with an applied power of 13 W.

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?10 V to a 5 ? copper film resistor for a few seconds and was found able to drive an intermediate layer of paraffin away and seal a 0.2 mm diameter circular via by wetting 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 85 ?C.

The Development of a Micro Machined Xenon Feed System

A Xenon feed system, manufactured by the means of micro machining, is under development. The system comprises several multifunctional modules described in the paper. A large part of the effort has been directed to the flow control unit, in which the flow is modulated using a thermal flow regulator. The regulator includes a heater and a temperature sensor, and has been manufactured and evaluated. A flow sensor is also included in the flow control unit. The mass for the xenon feed system, including housing and electronics is estimated to 150g.

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 1.0×10−8to1.0×10−4sccs gaseous helium under a pressure of up to 10bars 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.

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 silico ...

MEMS technology to achieve miniaturization, redundancy, and new functionality in space

Development of MEMS-based (Micro Electro Mechanical System) components and subsystems for space applications has been going on for at least two decades. The main driver for developing MEMS components for space is miniaturization through reduced mass, volume and power of individual components. However, the commercial breakthrough of MEMS has not occurred within the space business as it has within other branches such as the IT/telecom, the automotive industry, or other areas. In addition to miniaturization, increased redundancy and improved (or in some cases unique) performance has also been achieved by using MEMS-based components. MEMS pressure sensors integrated into the mechanical housing of another component is one example. Another example is an isolation valve which is both redundant and has an integrated particle filter on a single silicon chip weighing less than one gram. Currently there are few space missions using allowing newly developed MEMS devices onboard, but one of the exceptions is the Swedish-built Prisma satellites. One of the Prisma satellites has a MEMS-based cold gas propulsion system onboard, which contains a number of miniaturized and novel components. This paper presents the MEMS based cold gas propulsion system developed for Prisma including a number of novel components and their maiden spaceflight onboard Prisma last year.

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 the 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.

Development of MEMS-Based Components and Subsystems for Spacecraft Propulsion

Development of a MEMS-based (Micro Electro Mechanical System) components and subsystems has been pursued at Uppsala University, Sweden since 1997. Since 2005, the continued development towards the first flight the subject MEMS products onboard a satellite in 2008 is done within the frame of NanoSpace — a company dedicated to MEMS-based products for space. Currently, two major efforts to develop MEMS-based propulsion products are ongoing. First, NanoSpace is developing a miniaturized cold gas propulsion system. The major challenge in this effort is to develop the thruster module containing four individual thrusters with the capability to deliver proportional, low noise thrust in the micro- to milli-Newton range. The thruster pod even includes valves, filters, pressure- and temperature sensors and heaters. In a future step, even control electronics and a CAN interface will be included in the thrusters pod which has the size of a golf ball and a weight of about 100 grams. A prototype of this miniaturized cold gas propulsion will be flight tested onboard the PRISMA satellite. PRISMA is an international technology demonstration program with focus on rendezvous and formation flying. It is a two satellite LEO mission with a launch scheduled to September 2008. The other major development effort underway is a MEMS-based Xenon flow control system intended for electrical propulsion systems. Using MEMS technology, a Xenon feed system including an micro isolation valve, pressure regulator, and a number of parallel flow control modules can be built with significantly reduced size and mass compared to existing systems based on conventional technology. NanoSpace is a Swedish company with the goal to be a component and subsystem supplier of MEMS-based products to space industry, based on own research and development and intellectual property rights.© 2006 ASME

Development of MEMS-Based Spacecraft Propulsion

Development of a MEMS-based (Micro Electro Mechanical System) propulsion system has been pursued at Uppsala University, Sweden, since 1997. From 2005 and on, the continued development towards the first flight opportunity in 2009 is done within the frame of NanoSpace – a company dedicated to provide MEMS-based products for the space community. Currently, two major efforts to develop MEMS-based propulsion products are ongoing at Nanospace. Firstly, development of a miniaturized cold gas propulsion system. The major challenge in this effort is to develop a thruster module containing four individual thrusters with the capability to deliver proportional, low-noise thrust in the micro- to milli-Newton range. The thruster pod contains valves, filters, temperature sensors, heaters and nozzles. In a future step, even control electronics and a Controller Area Network interface (CAN) could/will be included in the thruster pod, which has the size of a golf ball and a weight of 60 grams. The first flight opportunity for this miniaturized cold gas propulsion system is the PRISMA satellites. PRISMA is an international (Sweden, Germany, France, Denmark, Norway) technology demonstration program, led by Swedish Space Corporation, with focus on rendezvous and formation flying. It is a two satellite LEO mission with a launch scheduled to first half of 2009. One of the satellites will act as a “target” while the other one will be a “chaser” that performs rendezvous and formation flying maneuvers. The current “chaser” design has the miniaturized cold gas propulsion developed by NanoSpace onboard. The other major development effort underway is a MEMS-based Xenon flow control system. Using MEMS technology, a Xenon feed system including an isolation valve, filters, pressure regulator, and a number of parallel flow control modules can be built with significantly reduced size and mass compared to existing systems based on conventional technology. The flight opportunity on PRISMA in 2009 represents a unique opportunity to demonstrate MEMS-based propulsion components in space, and thus take a significant step to enable greater satellite functionality, while significantly reducing cost and weight.