Abstract:
A microsatellite comprising a propulsion module for moving and/or pointing the microsatellite and an imaging device ( 100 ) mounted to the propulsion module. Furthermore there is a fuel supply ( 210 ) located within the imaging device ( 100 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Patent Application No. PCT/SG2008/000471 filed on Dec. 10, 2008 and which claims priority thereto, disclosures of which is hereby incorporated by reference in its entirety. 
     The invention relates to systems, modules and methods for the use of vehicles, such as those used for orbiting microsatellites, and the ancillary devices used therewith. 
     BACKGROUND OF THE INVENTION 
     Imaging from Space to Earth or other Space targets rely on the use of spacecraft equipped with cameras or telescopes using refractive or reflective lenses and sensor, detectors and attitude control devices such as thrusters, reaction wheels, gyroscopes to point such optical systems in the desired direction. Using more than one of such spacecrafts imaging the same target it may be possible to achieve a resolution higher than the one of each single optic. However, this requires precise knowledge and control of the relative position of the spacecraft. 
     Reaction wheels, gyroscopes and other “internal systems” are ineffective to control relative positions of spacecraft; the only useful systems are based on the action-reaction principle thereby requiring ejection of mass from the spacecraft to generate the needed thrust. Therefore all such thrusters require a container for the material to be expelled which is usually stored in a fluid form such as gas or liquid. Independently on the containment method and propulsion principle, the size of the container ultimately limits the maneuvering lifetime and therefore the usability of the imaging spacecrafts. A bigger container will allow for a longer lifetime for identical other parameters. 
     High resolution optics, in whichever part of electromagnetic spectrum, requires big focal lengths for high magnifications and large apertures to collect sufficient amount of radiation from the far away targets to impress the detection sensors. 
     For a given configuration and technology, a bigger optical system will allow for a higher quality image of better resolution. 
     It is therefore clear that propellant containers and optical systems are competing for volume available on the spacecraft when designing them for the best performances. Having such systems separately arranged on a spacecraft requires strong structures for both of them; in fact the propellant container has to withstand pressures and accelerations loads, while the optics needs high structural stiffness to guarantee precise positioning of the lenses. Such separate strong structures increase the total mass of the spacecraft and ultimately their manufacturing and launch costs. 
     SUMMARY OF INVENTION 
     In a first aspect the invention provides a microsatellite comprising a propulsion module for moving and/or pointing said micro satellite; an imaging device mounted to said propulsion module; a fuel supply; wherein said fuel supply is located within said imaging device. 
     In a second aspect the invention provides an electromagnetic valve comprising a substrate having an inlet port; a planar valve assembly said valve assembly comprising a valve frame and a selectively movable seat member co-planar with said static member; said planar valve assembly forming a layer on the valve frame; an electro magnetic coil having an axis perpendicular to a plane of said valve assembly; said electromagnetic coil being adjacent to said valve assembly; said seat member having a ferromagnetic material placed on a portion adjacent to said electromagnetic coil; wherein on energizing the electromagnetic coil the seat member is arranged to move within the plane of the valve frame towards said coil from a closed position sealing the inlet port to an open position opening the inlet port. 
     In a third aspect the invention provides an electromagnetic valve for selectively switching fluid communication between an inlet port and either a first and second outlet port the valve comprising a substrate having the inlet port; a planar valve assembly said valve assembly comprising a valve frame and a selectively movable seat member co-planar with said static member; said planar valve assembly forming a layer on the valve frame; an electro magnetic coil having an axis perpendicular to a plane of said valve assembly; said electromagnetic coil being adjacent to said valve assembly; said seat member having a ferromagnetic material placed on a portion adjacent to said electromagnetic coil; wherein on energizing the electromagnetic coil the seat member is arranged to move within the plane of the valve frame towards said coil from a first position opening the first outlet port and sealing the second outlet port to second position opening the second outlet port and sealing the first outlet port. 
     In a fourth aspect the invention provides an isolation valve for sealing a fluidic channel comprising a membrane located across the channel said member capable of withstanding pressure within said fluidic channel; a heating source congruent with said membrane; the heating source arranged to disrupt the membrane and so permit fluid flow across the membrane through the fluidic channel; wherein said heating source includes a resistor connected to a power supply said resistor having a heating surface congruent with said membrane. 
     In a fifth aspect the invention provides a multiple actuation valve comprising a block having an inlet and an outlet; a deformable membrane congruent with said inlet and outlet; a biasing member arranged to selectively bias the membrane into sealing contact with the inlet and outlet, wherein on removal of the bias applied by the biasing member, the deformable membrane is arranged to by deform to permit fluid communication between the inlet and outlet. 
     In a sixth aspect the invention provides a latch assembly comprising a housing; a socket within said housing, said socket and housing in rotational engagement about a central axis; a pin in sliding engagement with said housing from a retracted position to an extended position along said central axis; wherein in the retracted position, a first portion of the pin is shaped to prevent relative rotation of the housing and socket, and in the extended position a second portion is shaped to allow rotation of the housing and socket. 
     In a seventh aspect, the invention provides a support apparatus comprising a first and second magnet having axial magnetization and facing opposite polarity and positioned so as to generate a selectively adjustable repulsing force; the first magnet fixed to a bracket; the second magnet positioned above the first magnet in rotational engagement; wherein the second magnet is arranged to be mounted to a rotating device with the repulsive force adjusted to support the weight of the device and permit free rotation of said device through relative rotation of the first and second magnets. 
     In one embodiment, the present invention may combine optical and propellant containment systems in order to share efficiently volumes and structures. For this embodiment it is only required that the propellant material is sufficiently transparent to the electromagnetic waves that need to be collected by the detector sensor, the propellant material refraction properties are negligible or can be taken in to account in the design of the optical system and the structure can withstand the pressure of the propellant with negligible or controllable deformation. 
     In the following sections we will elaborate the general features of the invention with reference to a possible configuration while other configurations will be evident to the experts in the field by applying the general features of this invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       It will be convenient to further describe the present invention with respect to the accompanying drawings that illustrate possible arrangements of the invention. Other arrangements of the invention are possible, and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention. 
         FIGS. 1A ,  1 B and  1 C—A Microsatellite with a telescope mounted thereto according to one embodiment of the present 5 invention; 
       FIGS.  2 A and  2 B—A Microsatellite with a telescope mounted thereto according to a further embodiment of the present invention; 
       FIGS.  3 A- 3 E—A Micropropulsion module according to a further embodiment of the present invention; 
       FIGS.  3 F and  3 G—A micropropulsion module according to two further embodiments of the present invention; 
       FIGS.  4 A and  4 B—A Micro nozzle and Micro thruster module according to a further embodiment of the present invention; 
       FIGS.  5 A and  5 B—A Heater and Vaporisation assembly according to a further embodiment of the present invention; 
       FIGS.  6 A and  6 B—A Microvalve according to the prior art; 
       FIGS.  7 A- 7 D—Further Microvalves according to the prior art; 
       FIG.  8 —An Interdigitated electrostatic actuator according to the prior art; 
       FIGS.  9 A and  9 B—A Microvalve according to one embodiment of the present invention; 
       FIG.  10 —A Microvalve according to a further embodiment of the present invention; 
       FIGS.  11 A and  11 B—The Microvalve according to  FIG. 10 ; 
       FIG.  12 —The Microvalve according to  FIG. 10 ; 
       FIGS.  13 A- 13 C—The Microvalve according to  FIG. 10 ; 
       FIGS.  14 A- 14 C—A Microvalve according to a further embodiment of the present invention; 
       FIGS.  15 A and  15 B—A method of constructing a Microvalve according to one embodiment of the present invention; 
       FIGS.  16 A and  16 B—A method of constructing a Microvalve according to a further embodiment of the present invention; 
       FIG.  17 —A Microvalve showing an integrated pressure sensor according to a further embodiment of the present invention; 
       FIG.  18 —A Microvalve showing an integrated micronozzle according  5  to a further embodiment of the present invention; 
       FIG.  19 —An Isolation Valve according to one embodiment of the present invention; 
       FIGS.  20 A and  20 B—An Isolation Valve according to a further embodiment of the present invention; 
       FIGS.  21 A and  21 B—An Isolation Valve according to a further embodiment of the present invention; 
       FIGS.  22 A and  22 B—An Isolation Valve according to the embodiment of  FIGS. 21A and 21B ; 
       FIGS.  23 A and  23 B—The resistive heater according to the embodiment of  FIGS. 21A and 21B ; 
       FIGS.  24 A and  24 B—The resistive heater and isolation membrane for an Isolation Valve according to  FIGS. 23A and 23B ; 
       FIG.  25 —A characteristic of downstream Pressure-v-Time for an Isolation Valve according to  FIGS. 21A and 21B ; 
       FIGS.  26 A and  26 B—An isolation valve for multiple uses according to one embodiment of the present invention; 
       FIGS.  27 A and  27 B—A Pyrotechnic Latch according to a further embodiment of the present invention; 
       FIG.  28 —A Microbalance according to one embodiment of the present invention; 
       FIGS.  29 A and  29 B—A Microbalance according to a further embodiment of the present invention; 
       FIG.  30 —A characteristic of thrust versus time for various level of heating power for one embodiment of the present invention, and; 
       FIG.  31 —A Magnetic levitation bearing according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention involves a vehicle moving through space, such as a microsatellite traveling in an orbital path. The microsatellite according to the embodiment of  FIGS. 1A to 1C  and  2 A to  2 B includes an optical chamber, or tube  100  closed at one side by an optically transparent window  110  and at the other side by a flange  120  that allows for the placement of an optical detector  130  in correspondence with an opening  125 . The window  110  can also be conveniently shaped as a lens to perform a focusing or correction function in combination with the other lenses or mirrors that combine the optical system. The window  110  has at least the function of closing the tube  100  also with the help of a gasket so that the optical tube  100  can contain a pressurized fluid  200  to be used as propellant. The opening  125  allows for an optical detector  130  such as a CCD or CMOS to receive the image projected by the optical system of lenses and mirrors on the focal plane. The sensor  130  can be before or behind a cover  140  that close hermetically the optical tube  100  also thanks to a gasket. 
     A set of focusing and correcting lenses or mirrors can be placed inside the tube by means of spacers in a way commonly used in telescope optics with the only care of allowing for pressure equalization holes among the various sub-chambers created between the lenses. 
     In this configuration the elements  100 ,  110 ,  120  and  150  define a closed volume, such as a fuel supply or more specifically a fuel chamber  210  that contains the propellant fluid/fuel  200  preferably in the form of pressurized gas, but also possibly as liquid. 
     If the sensor  130  is inside the volume/fuel chamber  210  then its electrical and electronic connection cables will pass through the containing walls by means of a dedicated feed-through connector  220 . 
     For the purpose of clear explanation, the  FIGS. 2A and 2B  represent an optical configuration known as Matsukov-Cassegrain which typically guarantees a very compact volume with a considerably long focal length. The light from the imaged target first passes through the window  110  which has also the function of correcting lens to reduce the typical aberration of such kind of reflective optic. Then the light rays pass in the optical tube through the stored propellant gas and are reflected by the main mirror  160  placed at the end of the tube  100  on the flange  120 . After reflection they hit the secondary mirror  170  placed at the entrance of the tube  100  and are reflected back again until they reach the sensor  130  through the opening  125  in the main mirror and in the flange  120 . 
     If the optics are attached to various points of the tube  100 , care should be taken in the design to ensure negligible deformations of the tube under pressure so that the optical geometry is not disturbed. Alternatively the optics can be suspended to a structure internal to the tube and subjected to balanced pressures. 
     In case the variation of propellant refractive index due to changes in pressure and temperature need to be compensated, the optics can use deformable supporting structures ( 100 ,  101 ) composed by sealed chambers that deform in a shape canceling the optical effects on the fluid. 
     In case the propellant is stored in liquid form it is essential to avoid any liquid free surface or sloshing. This can be achieved by a bellow  260  inserted in the optical tube  100  and terminated by a flat transparent window  261  that contains the liquid  200  and contracts as it is used in order to keep it under pressure. The transparent window  261  will be part of a piston sliding inside the optical tube  100  and keeping pressurized the fluid by means of a spring or pressurized gas inserted in the chamber defined by the windows  261  and  110 . 
     Although this invention is applicable to any size of space imaging spacecraft, it shows its best advantages in the smallest satellites such as the Cubesats which have a typical square cross section of 100 mm.times.100 mm and length between 100 mm and 300 mm. With reference to a Cubesat satellite,  FIGS. 2A and 2B  show the propulsion module  300  attached to the optical tube and propellant main container  100 . In its configuration most efficient with respect of volume usage the propulsion module is also performing the function of secondary propellant container, whereby its internal volume  310  is connected to the optical tube volume/fuel chamber  210  through the window  125 . For optimal use of space, the optical sensor  130  and its electronics  135  as well as other satellite electronics  136  can be contained inside the volume  310  where they are also very well protected from space radiations by the metallic walls constituting the module  300 . 
     Placement for thruster modules  320  that control the attitude of a spacecraft is at the opposite corners of the spacecraft external envelope. It is also known that 2 couples of modules each with 4 nozzles  330  in cross and opposite configuration can control the attitude of the spacecraft on the 3 axes by subsequent rotations about two axis thanks to the torques achieved by firing opposite thrusters on opposite modules. 
     This invention allows the integration of such oppositthruster modules  320  at opposite corners a &amp; b of the propulsion module  300  without using any connecting pipe that is typically a risk of leakages and also of difficult assembly. The pipeless integration is obtained by screwing the thrust control valves  360  directly between the wall of the propulsion module and the thruster module. Since the valves  360  may still present a minimal leakage an isolation valve  400  is introduced to separate the actual gas volume  310  from the valve inlet volume  315 . For easy assembly and replacement the isolation valve  400  is attached to one of the corners of the micropropulsion module  300  left available by the thruster modules. A drilled channel connects the inlet of the valve  400  to the volume  310 , while another drilled channel  311  connects the outlet of the valve  400  to the plenum  315  drilled in the walls of the module  300  also connected to the thrust control valves  360 . The transversal channel  312  necessary to connect the isolation valve  400  with the thruster module  320   b  at the opposite corner is drilled in an internal rib of the module  300  that acts as structural stiffening element. Nearby the isolation valve is placed the gas filling check valve  362  and the pressure sensor  363  also connected to the volume  310  by means of drilled holes. 
     In order to allow the insertion of the sensor  130  and electronics  135  and  136  the micropropulsion module is shaped as a box with a lid attached by screws and sealed by a gasket. The lid can be joined or made integral with the flange  120 . 
     The electronic cables pass through the module wall  300  by means of feed trough connectors  305 . 
     For a higher amount of gas to be contained a pressure regulator  380  may be necessary to supply the various valves at lower pressure. The pressure regulator can be on the inlet of the isolation valve, at its outlet or between the main tank  100  and the secondary tank  300 , especially if the electronics  135  and  136  do not tolerate high pressures. 
     In order to achieve optical lengths longer than the total volume allowed during the satellite launch, an extendible structure may bring the first group of lenses forward once the satellite is deployed and ready to operate. This structure can be made by 2 or more sliding rods activated by compression springs or other extension actuators and released and locked in place by pyrotechnic latches  500 . Alternatively, the whole optical tube can be divided in cylindrical sliding sections  101  extending to the full length under the pressure of the propellant once the latches are released thereby reducing the pressure in the tank to produce less stress on joints and gaskets and less risk of leakages. Accordingly, this may act as stress relaxation on the structure to minimize or eliminate fatigue, creep or other detrimental time dependent effects. 
     The embodiment allows for the existence of a double hierarchy of chambers, the main chamber  210  containing the fuel and connected to the telescope volume, the second chamber connected to the thruster modules  320  by means of the thrust ports on the housing walls, the two chambers connected together by means of peripheral equipment (i.e. an isolation valve) that allows said connection only when thrust is required, otherwise isolating the main chamber from the second chamber to minimize or cancel the risk of leakages. 
     If the electronics  359  that control the valves  360  are placed inside the tank volume  320  to optimize the use of space, then the valves  360  can be conveniently placed inside the second chamber  315 , as shown in  FIG. 3F , thereby avoiding at least one fluidic joint and the related risk of leakages or reduced reliability. 
     For applications that do not require the use of optics integrated with the propellant containment, the lid can be simply flat and even soldered on the box if no electronic needs to be inserted. 
     The rest of spacecraft components  50 , other payloads and even commercially available photographic cameras can be attached by means of adapters to the bottom of the box or to the flat lid. 
     Micro Thruster Module 
     As shown in  FIGS. 4A and 4B  the thruster module  320  are mainly composed by a body  321 , a set of microvalves  360 , a microvalve gasket retainer  361  that compresses the sealing gaskets  362 , a set of micronozzles  330 , a micronozzle retainer  326  that lock them against the body  321  and compresses the sealing gaskets  326 , all assembled by screws. 
     Simplified versions may be made employing  3 ,  2  or even just one nozzle and valve. 
     Alternative embodiments include the use heating or vaporization of the propellant by introducing a resistor  381  in the duct  380  before the nozzle  330  as shown in  FIGS. 5A and 5B . Nozzle and duct are sealed by gaskets  382  and  384 , the resistor is connected to an external electric circuit by means of conducting wires  383  passing through the duct  380  which is made of high temperature insulating material such as machinable ceramic “Macor™”. The wires  383  are sealed by means of glass frit or similar means. The whole group is kept assembled by the head  386  and screws  387 . 
     Microvalve 
     Although commercially available microvalves are perfectly compatible with the described configuration, we present a novel microvalve which achieves size and mass reduction by possible full integration in the micronozzle without sacrifice simplicity of manufacturing and assembly. 
     Microvalves can be classified first in terms of manufacturing technology, which defines the general architecture, as MEMS or Precision Engineering microvalves. 
     MEMS microvalves, as any other MEMS device, are realized on a typical flat substrate (Wafer), which could be a combination of silicon, glass or plastic, in order to use photolithographic and etching batch processes. Precision engineering microvalves have a more three-dimensional structure enabled by individual machining, punching or molding of each component. 
     When aiming for high miniaturization, low price, high volume and high integration with other electronic devices, the MEMS approach is generally followed and is followed by the invention described here. As shown in  FIGS. 6A and 6B , typical MEMS microvalves are composed by a cavity realized in one of the substrates and closed by the other substrate which presents one hole that is the valve orifice. 
     Such valve orifice is then closed or opened by an actuator, often realized in the form of a membrane, moving perpendicularly to the flat substrates and actuated in different ways, typically by means of
         deformation of piezoelectric crystals subjected to high voltage   deformation of thermally actuated elements heated up by current flowing in to them using principles such as:
           thermal volume expansion of solid structure, fluid phase change or expansion;   shape memory alloy effect;   
               

     Examples of commercially available microvalves are shown in  FIGS. 7A to 7D , which represent a thermally actuated MEMS microvalve from the company Redwood Microsystems and an electromagnetically actuated precision engineering microvalve from the company Lee. 
     On the other hand, the performances obtainable with the use of electromagnetic effect are higher for the same actuator volume and energy used in terms of resulting speed and force on the actuator. This is due to the intrinsically higher energy density achievable with a well designed electromagnetic actuator. Another reason that normally discourages MEMS system to use the electromagnetic actuation is the complication in the realization of necessary coils and magnetic circuits due to material incompatibility, difficulty to be arranged in the typical flat architecture of MEMS and difficulty to realize the three-dimensional winding of the coil. 
     For these reasons, typical MEMS actuators use the effects mentioned above with the result of several drawbacks:
         weak actuation forces   need of high actuation power or voltage.   thermally actuated MEMS microvalves needs long time for the actuation due to the thermal inertia of the actuator in reaching the required opening temperature.   the temperature needs to be maintained during the whole actuation constantly providing the electrical energy to compensate the thermal losses through the actuator material. This results in a high electrical consumption of the microvalve.       

     At this point it must be reminded that the primary functions of a microvalve are:
         when closed: to provide a safe closing of a fluidic orifice without allowing any leakage   when open: to allow a good opening of the same orifice with minimum pressure drop in the flow of the fluid       

     For the first function it is necessary to guarantee a high closing force by means of springs or by means of the high pressure in fluid in the inlet channel; this force must be overcome by the actuator during the opening to perform the second fundamental function of the microvalve. 
     Therefore, the capability to obtain high actuation forces is fundamental for a good valve. 
     Additionally, the opening speed is very important to perform precise control of the amount of fluid allowed to flow. This can be achieved if the actuation force is high and it can be applied instantaneously. 
     As it will be explained in the following section, the invention described here makes full use of the electromagnetic actuation and its advantages in a MEMS microvalve specially conceived without facing the typical problems of electromagnetic actuation described before. 
     Differently from microvalves, in the micro positioning application the function of the moving part does not relate to any fluidic channel or orifice, therefore the movement can be directed along the flat surface of the MEMS substrates and the electrostatic principle of actuation has been generally used; typical structures in this case are commonly called “interdigitated” due to the fingerlike shape as clearly shown in  FIG. 8 . 
     By means of such principle, only very small forces may be generated, but they are generally sufficient for the actuation of microscopic parts internal to the devices, while such electrostatic forces are typically not enough to actuate a valve 
     The valve actuator is a miniaturized electromagnetic coil which axis is placed perpendicular to the substrate in which the microvalve mechanism is realized. This solution, not yet applied by any MEMS valve allows using relatively big magnetic circuit to actuate the microvalve mechanism. The moving part of the valve contains a little element of ferromagnetic material which interacts with the electromagnetic coil for the actuation. The axis of the electromagnetic coil is mounted out of the center of the ferromagnetic element at its resting position when the valve is closed. The actuation is achieved when the coil is energized and the magnetic field pulls the ferromagnetic element towards the centre of the coil to minimize the energy of the electromagnetic field. 
     The return and keeping in the closed position is realized by a spring embedded in the structure of the valve. The spring is preloaded during assembling of the valve by the insertion of the sealing element which is slightly thicker than the room provided for it at zero loading of the spring. Such preload guarantees the compression of the sealing element and therefore the absence of fluid leakages through the valve. 
     The extension of the actuator to the open position of the valve is limited by a stopper realized in the geometry of the actuator moving part; such limit guarantees that the stresses in the spring element are kept under the levels compatible with the elastic behavior of the material and well below the yield margin of the material. 
     The fluidic valve is mainly composed of the same basic elements as any other valve such as described earlier, which are here arranged in a planar fashion along the substrate material in a particular embodiment: inlet channel  5009 , orifice  5010 , sealing gasket  5005 , gasket seat  5003  outlet channel  5011 , closing element  5003 , spring  5004  and actuator  5020 . The electromagnetic actuating solenoid  5020  with its coil  5021  can be arranged independently from the substrates in any position suitable for the magnetic field to interact with the moving element. A possible configuration is shown in  FIGS. 9A and 9B . 
     The microfluidic planar part of such configuration can be realized by means of Etching technology on silicon and it requires 2 internal silicon layers  5102 ,  5103  and  2  external glass layers  5101 ,  5104  in its most efficient embodiment as shown in FIG.  10 —4 layers valve construction: a) view; b) cut view  FIG. 10 ,  FIGS. 11A and 11B  and  FIGS. 13A to 13C . 
     The four layers construction  5100   a - d  has the spring  5004  and moving body  5002  split in two symmetric parts (i.e.  5004   a  and  5004   b ) with the orifice  5010  realized in between them. This symmetry is necessary to allow a perfectly symmetrically aligned loading of the spring  5004  pressing the gasket  5005  on its seat  5002 . 
     As shown in  FIGS. 13A to 13C , the opening of the valve is achieved with the translation of the moving body  5103  by the action of the electromagnetic field provided by the electromagnet  5120  when its coil  5121  is energized and attracts the anchor  5122 . In this situation the moving body  5103  releases its pressure on the seal  5105  and the fluid is allowed to flow from the inlet channel  5109  through the opened orifice in the outlet channel  5111  that can be made exiting perpendicularly to the substrates or parallel to them in a micronozzle  5090 . 
     It must be noted that the sealing  5105  is inserted in a slot between the moving body and the orifice seat. Such slot is realized by manufacturing at a slightly smaller size than that of the gasket in order to compress the inserted gasket by means of the extension required to the spring  45004  when the gasket is in place. This special feature may allow the complete valve body, spring, moving body, orifice and gasket seat to be formed as only one monolithic part. 
     A simplest embodiment  5200  is possible using only two wafers (named “2 L” microvalve) for fabrication in facilities with less experience. In this case, only half of the sandwich will be realized using only one silicon wafer  5201  and one glass wafer  5202  and the structure will not be symmetric about its mid plane and it will be completed by inserted the chip in a packaging  5203  providing the bottom of the inlet  5209  and outlet fluidic connections. This simplifies the alignment requirements during the bonding and double side etching, but introduces a small asymmetric behavior in the extension of the spring  5204  and in the compression of the sealing element. 
     The fluidic passages are then completed by pressing the two-wafer sandwich chip in a packaging with a profiled seal  5212 . Such package can be made in any material provided it is diamagnetic and it allows to keep the magnetic circuit with minimum gaps. 
     As shown in the  FIGS. 13A to 13C  and  FIGS. 14A to 14C  this embodiment has been configured to have one inlet  5209  and two outlet channels  5211   a  and  5211   b  as well as two gaskets  5205   a  and  5205   b  so that the valve can have one channel open for return of fluid at any time while the other is closed. 
     The process for the realization of the 4 L microvalve requires a combination of Deep-Reactive Ion Etchings, fusion and anodic bonding and dicing as depicted in  FIGS. 15A and 15B . The two silicon wafers  5102  and  5103  are lithographed and etched on both faces to create the channels, and to create the gap that will allow the moving part to translate and they are etched through to create the elastic spring and allow the movement of the moving part. 
     The four layers construction  5100  has the spring  5004  and moving body  5002  split in two symmetric parts (i.e.  5004   a  and  5004   b ) with the orifice  5010  realized in between them. This symmetry is necessary to allow a perfectly symmetrically aligned loading of the spring  5004  pressing the gasket  5005  on its seat  5002 . 
     As shown in  FIG. 13 , the opening of the valve is achieved with the translation of the moving body  5103  by the action of the electromagnetic field provided by the electromagnet  5120  when its coil  5121  is energized and attracts the anchor  5122 . In this situation the moving body  5103  releases its pressure on the seal  5105  and the fluid is allowed to flow from the inlet channel  5109  through the opened orifice in the outlet channel  5111  that can be made exiting perpendicularly to the substrates or parallel to them in a micronozzle  5090 . 
     It must be noted that the sealing  5105  is inserted in a slot between the moving body and the orifice seat. Such slot is realized by manufacturing at a slightly smaller size than that of the gasket in order to compress the inserted gasket by means of the extension required to the spring  5104  when the gasket is in place. This special feature may allow the complete valve body, spring, moving body, orifice and gasket seat to be formed as only one monolithic part. 
     A simplest embodiment  5200  is possible using only two wafers (named “2 L” microvalve) for fabrication in facilities with less experience. In this case, only half of the sandwich will be realized using only one silicon wafer  5201  and one glass wafer  5202  and the structure will not be symmetric about its mid plane and it will be completed by inserted the chip in a packaging  5203  providing the bottom of the inlet  5209  and outlet  5210 ,  5211  fluidic connections. This simplifies the alignment requirements during the bonding and double side etching, but introduces a small asymmetric behavior in the extension of the spring  5204  and in the compression of the sealing element  5205 . 
     The fluidic passages are then completed by pressing the two-wafer sandwich chip in a packaging with a profiled seal  5212 . Such package can be made in any material provided it is diamagnetic and it allows to keep the magnetic circuit with minimum gaps. 
     As shown in the  FIG. 13  and  FIG. 14  this embodiment has been configured to have one inlet  5209  and two outlet channels  5211   a  and  5211   b  as well as two gaskets  5205   a  and  5205   b  so that the valve can have one channel open for return of fluid at any time while the other is closed. 
     The process for the realization of the 4 L microvalve requires a combination of Deep-Reactive Ion Etchings, fusion and anodic bonding and dicing as depicted in  FIG. 15 . 
     The two silicon wafers  5102  and  5103  are lithographed and etched on both faces to create the channels, and to create the gap that will allow the moving part to translate and they are etched through to create the elastic spring and allow the movement of the moving part. 
     Before proceeding with the fusion bonding of the two silicon wafer the gasket, realized in a soft metal able to withstand the bonding temperature must be inserted in place. 
     Before proceeding with the anodic bonding of the bottom layer of glass, the anchor made of ferromagnetic material is put in place. 
     After the 3 bonding steps are completed the chips are diced from the wafer. 
     As shown in the  FIGS. 16A and 16B  the process for the realization of the 2 L microvalve require a similar set of steps, but simplified due to the absence of difficult bonding alignment requirements and due to the accessibility of seat and anchor cavity after bonding and dicing, so that low temperature materials can be used for the seal (i.e. rubber) and for the anchor (i.e. magnetized alloys) 
     A pressure sensor can be easily integrated in the system by taking advantage of the deformation of the chamber of the valve under pressure. As shown in  FIG. 17 , an electrodeposited and lithography patterned layer of resistors  5301   a  to  5301   d  and conductors will realize a Wheatstone bridge which electric unbalance produced by the chamber deformation can be detected by an external circuit and correlated to the internal pressure. The electrical connection will be realized by probes or wire bonding or by soldering to the electrode pads  5302   a  to  5302   d.    
     The outlet of the valve can be connected on the hole realized on the bottom  5111  or on the side of the chip  5090  through a convergent divergent micronozzle, thereby realizing a fully integrated MEMS controllable microthruster or micro-mass flow controller as shown in  FIG. 18 . 
     Characteristics of the electromagnetic valve according to various embodiments of the present invention include:
         i. its movement parallel to the substrates, while all the actuators developed for similar functions are moving perpendicular to the substrates   ii. the actuation by means of energy provided by an external electromagnetic field created by a solenoid completely decoupled by the actuator itself, while all the other similar actuators are working on thermal-expansion or electrostatic or piezoelectric system requiring a much intimate contact of the energy providing element with lower energy densities, higher complication and cost.   iii. The design based on only 1 simple and reliable micromachining process, namely Reactive Ion Etching (RIE) and two simple and reliable packaging processes, namely Anodic Bonding and Silicon Fusion Bonding.   iv. The opening of the microvalve seat in the direction parallel to the substrates   v. The closing force and preload of the microvalve produced by means of springs realized in the bulk of the substrates   vi. The realization of valve body, moving element, elastic element, orifice, gasket seat in one monolithic part   vii. The integration of a separate sealing element that can be inserted in the assembly allowing for the choice of virtually any material depending on the final destination of use (i.e. aggressive fluids)   viii. The absence of contact of the circulating fluid with any electrical part of the system   ix. The use of the microvalve as MEMS integrated microdruster   x. The use of the microvalve as MEMS integrated micro flow controller
 
Isolation Valve
       

     The isolation valve  400  is made in two different configurations: single actuation and multiple actuation. 
     The single actuation valve is based on a membrane melted by a small resistor reaching high temperature by Joule effect. 
     As shown in  FIG. 19 , the thermally actuated isolation valve is composed by a thin membrane  4005  supported on a robust diaphragm  4003  with holes  4006  which separate the tank volume from the piping connection. The membrane is weakened and eventually locally melted by a heater  4004  in order to allow the pressure of the gas in the tank to brake the membrane and open the valve. The supporting diaphragm is placed between the tank body  4001  and the piping collector body  4002 . 
     The heater  4004  is a commercial Surface Mounted Device resistor of 50 Ohm or two or more of them placed on the sides around the hole  4006  for a total resistance of 100 Ohm in a combination of parallel and series (two resistors of 100 Ohm in parallel or two parallel couples of 25 Ohm resistors in series). A voltage of 12V is applied to the resistors  4004 . 
     There are two basic configurations, one in which the fluid passes through the valve in one direction (named “T”), suitable to be mounted between threaded pipes or between a tank and a threaded pipe and a second one in which the fluid passes through the valve and returns on the same side where it entered after the opening of the valve, (named “R”). 
     As shown in  FIGS. 20 to 24 , the membrane  4105  is supported by a printed circuit board, “PCB”  4103  also supporting one or more resistors  4104  to which it provides electrical connections. The membrane  4105  and the PCB  4103  are sandwiched between the body  4101  connected to the pressurized tank and the body  4102  connected to the downstream piping. The resistors  4104  are placed besides one or more holes  4106 . The complete sandwich is leak free thanks to two gaskets  4107  and packed by means of screws  4108 . 
     The basic embodiment of the valve “R” is made by a main body  4201  and a closing head  4202  sandwiching the membrane  4205  and its support  4203  carrying the resistors  4204  and presenting holes  4206  for the passage of the gas through the valve. 
     The difference with the valve “T” is evident by observing the function of the head  4201  to redirecting the flow to the main body  4201  through a second hole in the membrane support  4203 . In this way, provided the tank mantel or case contains also the downstream channel, the isolation valve “R” is of easier replacement operating only from one side of the tank and not between tank and piping as in the case of the valve “T”. 
     There are two variations in the embodiments for the isolation valve “R”, one in which the body of the valve is made by two bulky bodies  4201  and  4202 , named “RB”, and one in which the valve is a sandwich of thin substrates (named “RS”). The main difference consists in the sealing used between the membrane and the downstream body. Such body is in contact with the backside of the PCB supporting the sealing membrane. 
     In the case of the bulky bodies, as shown in  FIGS. 21A and 21B , the sealing is achieved by means of micro O-Rings  4207  compressed between the bodies and micropipes  4209  that runs between the bodies thereby creating alignment to the tank and solidity of the system. 
     In the case of the sandwich “RS” the sealing is obtained, on one side in the same way as the bulky bodies, while on the other side by means of soldering of pre-tinned surfaces on the substrates. 
     In any case the membrane is glued on the heater substrate by means of an additional sticky tape layer  405   a  or being itself realized by punching from a sticky tape. 
     The choice of the membrane material must be such as to be able to withstand normal high temperature up to 150 C and low temperature down to −50 C, and at the same time it must be able to reach melting point at around 250 C before the heat produced by the heater reaches other vital elements such as the O-Rings  4207  or more peripheral areas of the membrane thereby. A typical opening time of 500 ms is obtained and a complete opening is stabilized by keeping the heating as long as 1 s or 2 s. The opening of the valve can be observed by monitoring the downstream pressure rising as shown in  FIG. 25 . 
       FIGS. 26A and 26B  show a multiple actuation valve, here represented as a modification of the previous single actuation “R” isolation valve, is based on a rotating cam  4510  moved by an electric motor which  4520  closes and opens a deformable membrane  4530  placed between body  4201  and head  4540  of the valve. The motor, using a reduction gearbox if necessary, moves a biasing member, in this case a sliding element  4560 , by means of the eccentric cam  4510  mounted on its shaft. The sliding element pushes the deformable membrane  4530 , possibly made in rubber, which is pressed against the inlet and outlet holes as well as against the flat region between the holes thanks to a tight tolerance assembly. When the sliding element  4560  is lifted due to the cam rotation, the membrane is deformed by the pressure of the fluid from the inlet hole and the fluid starts to flow along the channel created by the deformation of the membrane. The valve is completely opened and closed at each half turn of the cam. 
     Characteristics of the isolation valve according to various embodiments of the present invention include
     i. The use of a membrane to interrupt and seal a fluidic channel or pipe to separate a higher pressure side from a lower pressure or empty side   ii. The possible use of a polymeric membrane with one or both sides prepared with glue or sticky material to create a seal between the membrane and the body in contact   iii. The use of one or more resistors to melt such membrane in one or more points so to allow the flow of the fluid through it.   iv. The placement of the resistors with the heating surface at the same level of the surface supporting the sealing membrane.   v. The positioning of the resistors around a hole in the membrane supporting element in order to melt the sealing membrane closing such hole.   vi. The use of a sandwich structure to realize the channel to be sealed in a way transversal to the sandwich layers.   vii. The assembly of the sandwich structure by using soldering material.   viii. The use of the pressure in the pressurized side to press the sealing membrane on the resistor heating surface thereby obtaining the best heat transfer to melt the membrane   ix. The possibility to obtain a returning channel to convey the flow, once the sealing membrane has been opened, back to the same side it was originated, thereby creating the possibility to mount the isolation valve on a side of the tank, for easy replacement in case of re-use or in case of need multiple use for testing purposes.
 
Pyrotechnic Latch
   

     The pyrotechnic latch  500  can be “protruding pin” or “rotation locked” and is based on a small explosive charge  510  such as a mixture of Potassium Perchlorate and Aluminum powders ignited by a small resistor and displacing a small piston  530  which moves a protruding tip or disengage a rotating element. 
     The protruding pin latch is a simplified version of the rotation locked which will be described here. 
     The latch is mainly composed by a body  550  and a shaft  530 , the shaft has a chamber  535  at its inner end and a small Printed Circuit Board (PCB)  560  is inserted from a slot in the body  550  to complete such chamber volume. Such PCB has at least one small resistor  560  facing the chamber volume and connected externally to an electric circuit by means of isolated leads along the PCB. The other end of the shaft has a square section  536  which engages with a retainer element  570  screwed on the body and with the hub  580  attached to the body by means of a bearing  585  or equivalent rotating joint. Retainer and Hub have a rectangular slot  590  that does not allow the relative rotation of shaft, retainer and hub. The chamber is filled with explosive material  510  which is ignited if current passing in the electric circuit heats up the resistor and the adjacent explosive material to the ignition temperature. The resulting explosion pushes the shaft  530  forward as shown in  FIG. 27   b  and disengages its square end  536  from the retainer and hub presenting a circular portion  537  to their rectangular slot. At stroke completed the conical mating  538  between shaft and retainer is locked thanks to its small angle. In open configuration the hub is now free to rotate and the shaft is locked in open position. 
     Microbalance for Thrust Measurements 
     The thrust measurements have been realized by means of a new microbalance, based on the concept of torsion balance and modified by using a hollow pipe  2305  to supply the pressurized propulsion fluid from an external tank  2304  and to provide the elastic element sensing the thrust force whose deformation is measured at the tip of the arm  2306  where the thrust is produced by the thruster  201 . The elastic torsion suspension removes the presence of any friction therefore allowing, in combination with an optocoupling circuit or radio to actuate the thruster valve  220 , the measure of the exact force produced by the microthruster. If the optocoupler is not used, very thin conductors attached to a flange  2309  can be added to the system and the small additional stiffness introduced can be numerically deducted by the measurement of the oscillation period with and without such wires. Alternatively the valve can be placed upstream the elastic pipe loosing the capability to create very small thrust pulses but allowing for perfect elastic suspension. 
     There are two measurement methods possible: by allowing deflection which is then detected  2310  by optical means (i.e. laser displacement meter) or by compensating the thrust with another external and contactless reference and controlled force produced electrically (i.e. electromagnetic or electrostatic force). 
     The realization of the balance requires a perfect equilibrium of the various suspended masses in order to place the center of mass exactly below the hollow pipe  2305 . Furthermore, the pipe must be of very small diameter and thickness to allow for the smallest thrust forces to generate enough deflection force and in the same time, the pipe  2305  must be strong enough to suspend the whole oscillating part and to withstand the gas internal pressure. 
     The pipe  2305  is connected to the upper and lower flanges by means of glue, the upper flange is connected by means of a screw on the ceiling of the vacuum chamber in which the thrust is measured, and the lower flange is connected by screws to the lower flange that hold the balance arm and the equilibrium counterweight. 
     When the balance is operated by switching on the microthruster at the end of its arm, the force produced by the micronozzle  201  turns the arm  2306  around the suspension pipe  2305  and a dynamic oscillation starts according to the difference between thrust-torque and elastic reaction torque of the pipe. Since such two forces are generally not equal, the balance continues its forced harmonic oscillation which is measured by the laser sensor and since the elastic reaction produced by the suspending pipe  2305  is well known due to the material and geometry of the pipe  2305  and since the inertia of the balance is known by design and confirmed by free harmonic oscillation period measurements, the only unknown is the force produced by the micronozzle which can be therefore calculated versus time. For the case of the propellant heating microthruster configuration, a set of typical diagrams of such oscillations is shown by the red line in the  FIG. 30  which also shows on the blue line the pressure in the gas tank. Due to the use of a paper recorder, the time direction in the diagrams is from right to left. It can be clearly noticed how the oscillation amplitude (and therefore the thrust of the micronozzle) are reducing as the pressure is reduced by the use of the gas available in the tank. 
     Magnetic Levitation Bearing for Full Micropropulsion System Characterization 
     In order to test the complete micropropulsion system it is necessary to operate it in a vacuum box with a suspension that presents the smallest possible friction. Although the following description relates to the solution of such problem for the case of the micropropulsion, the present solution to such problematic can be applied to any instrument or device which includes a rotating equipment of relatively high weight in relation to its rotational friction. 
       FIG. 31  shows a support apparatus to achieve this which, in this embodiment, includes two ring magnets with axial magnetization in relative rotational engagement, said magnet consequently forming a magnetic levitation bearing. It will be appreciated that in some embodiments, such as when rotational friction is less critical, that the ring magnets may be replaced by a circular array of magnet sections, which may emulate a complete ring magnet. 
     Such bearing is placed in closest proximity and slightly higher than the center of gravity  6010  of the complete micropropulsion system assembled with the microsatellite components necessary for wireless control and telemetry as well as power supply. The bearing is realized by two ring magnets  6020   a  and  6020   b  with axial polarization and opposite polarity with typical magnetic field lines  6060 . One bearing is fixed on the levitating micropropulsion structure  6030  while the other is on top of a column  6040  reaching inside the microsatellite and fixed on a base  6050  capable of precise vertical alignment by means of adjustment screws and leveling bubble. Since two opposite magnets do not form a perfectly stable system it is necessary to guarantee a lateral alignment of the two repulsive forces and the gravity force. This is achieved by means of a needle  6100  protruding from one of the two parts (i.e. the column) and engaging a concave seat  6110  in the other part (i.e. the levitating object such as the microsatellite under testing). The distance between the two magnets is kept by the needle-seat at a value insufficient to generate a force that completely balances the weight of the levitating body. In this way there is still a small force keeping the needle  6100  in the center of the seat  6110  and therefore anchoring the two parts together in a stable way. Since such residual force can be selectively reduced by fine tuning the magnet distance thanks to a sliding support  6200 , also the friction can be reduced at minimal values also for very heavy levitating masses. By means of this system small lateral oscillations around the contact point needle-seat are allowed which are useful to judge the alignment of the thrusters and distribution of masses. 
     Having a very low friction compared with any classical bearing, the smallest effects of the microthruster forces can be evaluated and the actual resolution and impulse capability of the micropropulsion system can be fully characterized and demonstrated.