Abstract:
An electrothermal deployment system may be configured for controlled release of various apparatus from their prelaunch stowage positions in small satellites. The deployment system includes a fusible line secured to a structural component of the satellite, as well as to various deployable apparatus secured to, within, or on the satellite. The deployable apparatus may include items such as solar panels and antennas. The deployment system includes an electrically resistive element such as a burn bar formed of a cylinder or tube, including a resistor pad overlying and/or incorporated within an exterior surface of the burn bar. The burn bar may be coupled to an electrical circuit configured to heat the resistor for the purpose of melting the fusible line secured in direct contact therewith, thus causing the fusible line to break to cause deployment. The fusible line is configured to remain in secure contact with the resistor until apparatus deployment.

Description:
FIELD 
     The present disclosure relates generally to deployment of equipment stowed in or on a very small satellite, and more specifically to devices configured for electrothermal deployment of apparatus such as solar panels and antennas from their launch-secured stowage positions aboard such satellites. 
     BACKGROUND 
     Very small satellites having a wet mass of between 1 and 10 kg. (2 to 22 lbs.) have been commonly termed “nanosats”. Satellites of this category, which may be as small or smaller than a loaf of bread, are relatively inexpensive to build, but are typically very delicate structures. They may be configured to carry onboard computers adapted to interface with communication systems designed to not only control directional stability including orbit commands, but also to permit deployments of onboard apparatus, such as solar panels and antennae, from their prelaunch stowed positions to their operational positions on an orbiting satellite. 
     Weight management is critical with respect to design and operation of a nanosat. As such, normal earth-bound structures such as spring-loaded latches and motorized structures to operate such devices, even when miniaturized, may be too massive for consideration for use in a nanosat. Instead, alternatively designed structures are often developed to manage nanosat functions. 
     For example, the simple operation of remotely uncoupling a solar panel or an array of antennae may require use of electrically controlled structures involving extremely lightweight elements. Achievement of sufficient combinations of strength and lightness can be challenging, particularly when pre-testing protocols may be required to qualify various parts for dependable operability. Indeed, the latter protocols may require that some parts critical to the deployment function may be subjected to several prelaunch cycles to demonstrate satisfactory repeatability, i.e. more than single use functioning without failure, in order to qualify for launch readiness. 
     One known deployment system used in prior nanosat structures has involved use of thin coiled nichrome wiring configured for melting a nylon fishing line adapted to release or deploy apparatus such as solar panels and antennae. Issues with the coils, including their overheating, fusing, and/or breaking prior to sufficiently heating the nylon to its melting point, as well as lack of system repeatability, have created a need for more reliable deployment structures. 
     It is therefore desirable to provide improved deployment systems for nanosats. 
     SUMMARY 
     In accordance with one aspect of the present disclosure, an electrothermal system is configured for controlled release of deployable apparatus relative to small satellites. The deployment system includes an electrical power source and a thermal energy release device in communication with the power source. 
     In accordance with another aspect of the present disclosure, a resistive element is configured to generate heat via the electrical power source to melt a fusible line, configured in one form as a monofilament, affixed to a structural component of the satellite to release at least one deployable apparatus secured to the satellite. 
     In accordance with another aspect of the present disclosure, the fusible line is configured for direct contact with the energy release device, and is melted by heat produced by the energy release device for deployment of the apparatus. 
     In accordance with another aspect of the present disclosure, a burn bar is adapted to melt a fusible line to cause deployment of an apparatus secured to a small satellite. The burn bar includes a substrate body secured to the satellite, and has an insulative material deposited on an outer surface of the substrate, and a layer of electroconductive material deposited over portions of the insulative material. 
     In accordance with another aspect of the present disclosure, a fusible line is secured against the electroconductive material, and the electroconductive material is heated, causing the fusible line to reach its melting point to cause release of apparatus secured to the fusible line. 
     In accordance with another aspect of the present disclosure, a method of deploying an apparatus secured by a fusible line to a nanosat includes steps of providing a metal substrate, securing the substrate to the nanosat, depositing an insulative material on a peripheral surface of the substrate, and depositing a layer of electroconductive material over portions of the insulative material. 
     In accordance with another aspect of the present disclosure, the method further includes providing an electrical source within the nanosat, and connecting the electroconductive material to the electrical source, stringing a fusible line over the electroconductive material, and securing the fusible line to the nanosat, and attaching the fusible line to the apparatus to be released. 
     In accordance with another aspect of the present disclosure, the method further includes stringing the fusible line against the electroconductive material under tension, providing an electrical current from the electrical source through the electroconductive material, the electrical current being sufficient to heat the fusible line to its melting point to release the apparatus. 
     In accordance with yet another aspect of the present disclosure, the method further includes laser etching the electroconductive material to form a resistor, and providing an electric current from the electric source through the resistor sufficient to heat the fusible line to its melting point. 
     The features, functions, and advantages disclosed herein can be achieved independently in various embodiments or may be combined in yet other embodiments, the details of which may be better appreciated with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary perspective view of a small satellite that incorporates the electrothermal deployment system of the present disclosure. 
         FIG. 2  is a perspective view of the satellite of  FIG. 1 , but with a solar panel shown in a deployed position. 
         FIG. 3  is a front elevational perspective view of an interior portion of the satellite of  FIGS. 1 and 2 . 
         FIG. 4  is an enlarged perspective view of a portion of the view of  FIG. 3 . 
         FIG. 5A  is a perspective view of a second embodiment of the electrothermal deployment system of the present disclosure. 
         FIG. 5B  is a perspective view of a third embodiment of the electrothermal deployment system of the present disclosure. 
         FIG. 5C  is a perspective view of a fourth embodiment of the electrothermal deployment system of the present disclosure. 
     
    
    
     It should be understood that the drawings are not to scale, and that the disclosed embodiments are illustrated only schematically. It should be further appreciated that the following detailed description is only exemplary, and not intended to be limiting. As such, although the present disclosure is, for purposes of explanatory convenience, depicted and described in only illustrative embodiments, the disclosure may be implemented in numerous additional embodiments, and within various additional systems and environments not shown or described herein. 
     DETAILED DESCRIPTION 
     The following detailed description is intended to provide both apparatus and methods for carrying out the disclosure. Actual scope of the disclosure is as defined by the appended claims. 
     With respect to references to elements depicted in the drawings, as each new embodiment is introduced the elements that are similar to those in previously introduced embodiments will share similarly numbered relationships, though separated by a multiple of one hundred, unless otherwise indicated. For example, the resistive element, i.e. the burn bar  42 , of the deployment device  40  is depicted in  FIG. 1  as element  42 , in  FIG. 5A  as element  142 , and in  FIG. 5B  as element  242 , etc. 
       FIG. 1  illustrates a very small commercial satellite, called a “nanosat”  10 , which incorporates a deployable panel  12 . The panel  12  incorporates a panel release mechanism  14  to which may be secured a fusible line as described below. The nanosat  10  incorporates structural frame, including elements  16 ,  18 , adapted to support all contents of the nanosat, including communications equipment, stabilizer elements, antennas, and the like. 
     Referring now to  FIG. 2 , a solar panel  20 , constituting an opposite side of the deployable panel  12  of  FIG. 1 , is shown as deployed from its prelaunch or stowed position (of  FIG. 1 ). In the deployed position, it will be appreciated that the solar panel  20  has been released by virtue of the panel release mechanism  14 , as further described below. It will also be appreciated that the solar panel  20  may be hinged to the structural frame element  18 , and stowed against a non-deployable interior panel  22  for, inter alia, assuring a compact envelope for pre-stowage of the nanosat  10  within a deployable launch module (not shown). Such launch module would normally be carried aboard an earth-to-orbit rocket (not shown). Although this embodiment may depict the solar panel  20  as the only panel containing solar cells (not shown), this disclosure is not to be construed as being so limited. For example, the exterior deployable panel  12  of  FIG. 1  may contain solar cells as well. 
     Contained within the body of the nanosat  10  are various satellite components, including stabilizer elements  24 , as shown. The structural frame elements  16 ,  18  are secured rigidly together via structural support beams  26 ,  28 ,  30 . In the described embodiment, the support beam  30  (exterior face shown, only) may be configured to contain a deployment device of the present disclosure. 
     Thus, referring to  FIG. 3 , an interior face  32  of the support beam  30  contains a deployment device  40 , as shown. Referring also to  FIG. 4 , the deployment device  40  contains an electrically resistive element  42 , herein also called a burn bar  42 , depicted as a solid cylinder, but which may also be tubular, or have a variety of other shapes, some of which are shown and described below as alternative embodiments. On an exterior surface of the burn bar  42 , an electric resistor pad  44  may be etched from an applied electroconductive material coated over the exterior surface of the burn bar  42 . 
     The burn bar  42  may be attached to the support beam  30  via epoxy to avoid weight of conventional weld materials. In the described disclosure, the solid cylinder or tubular burn bar  42  can provide a more robust heat sink than a simple resistive flat-styled burn bar (not shown). As such, it will be apparent to those skilled in the art that heat released from the resistor pad  44  may be better isolated via the cylindrical or tubular burn bar substrate from transfer into the physical nanosat structure, i.e., the support beam  30 . As such, the described configuration may require less electric power for deployment, while minimizing undesirable heat transfers to adjacent structures. 
     An electrical wiring harness  48  is secured to the burn bar  42  as shown. A positive electrical lead  50  and a negative electrical lead  52  have their respective ends  54 ,  56  secured to opposed sides of the burn bar  42 , more specifically to lead connection structures  58 . A fusible line  60  is secured tightly across the burn bar  42 , and specifically at a position to make direct contact with the resistor pad  44 . The fusible line  60  as shown and described herein is a single strand or monofilament. Such fusible line  60  may alternatively consist of a multi-strand line in appropriate scenarios, e.g. one requiring higher load-bearing, for example. An electrical source  36  (shown schematically in  FIG. 4 ) is contained within the nanosat  10 , and may be configured to apply sufficient voltage to the resistor pad  44  to physically heat the resistor pad to melt the fusible line  60  for achieving desired deployment, from prelaunch stowage position, of onboard satellite apparatus such as the solar panel  20 . 
     In the disclosed embodiment, the burn bar  42  may be configured for a lower voltage requirement than known prior art configurations. As such, it can be made robust enough to be reusable, as may be required under various test repeatability protocols, particularly to assure that a given burn bar will melt the fusible line  60  in a predetermined amount of time. The burn bar  42  may be configured as a printed heater embodiment, or may alternatively be configured as a simple non-printed resistor. 
     The fusible line  60  may be secured to the deployable solar panel  20  in a manner to assure direct contact between the line  60  and the resistor pad  44  for reliable deployment. For this purpose, those skilled in the art will appreciate that the line  60  may be strung under a tensile load through spaced apertures  70 ,  72  ( FIG. 4 ) of the frame support beam  30 , for connection of respective ends  62 ,  64  of the line  60  to the above-described panel release mechanism  14  (see  FIG. 1 ). The apertures  70 ,  72  may be chamfered to avoid chafing or damage to the fusible line  60 . 
     For convenience, particularly prior to launch of the nanosat  10 , a line guide  80 , depicted herein as a tube, may be utilized for control of one or both free ends  60 ,  64  of the fusible line  60  prior to securement thereof to the panel release mechanism  14 . In order to secure the guide  80 , a recess or channel  82 , sized and shaped to at least partially countersink the guide  80 , may be formed in the support beam  30 , as shown. Alternately, the guide  80  may be secured to the support beam  30  by an adhesive or bonding agent, such as an epoxy (not shown). 
     Example 
     By way of illustration only, the fusible line  60  may be formed of a fusible material of approximately 3.0 thousandth of an inch diameter, capable of bearing approximately at least 5, and up to 40, tensile pounds of force, as a nylon fishing line, for example. The resistive element or burn bar  42  may be of a solid or tubular structure, and the resistor pad  44  may be formed on an exposed exterior surface of the burn bar. The burn bar may be configured such that the burn bar  42  may be subjected to approximately 5-12 volts for less than 15 seconds, for example 3-8 seconds, to satisfactorily heat and melt the fusible line, which will typically heat up faster in a space or vacuum environment, as compared to an atmospheric environment. For both weight control and performance, the substrate body  46  of the burn bar  42  may be formed of an aluminum alloy. The burn bar  42  may be formed as part of a printed circuit board, and may be approximately 80 thousandths of an inch diameter, and configured to satisfactorily handle 12 volts without failure for achieving reliable and satisfactory electrothermal deployment. The positive and negative lead lines  50 ,  52  may each be of 30 gauge thickness, and may be formed of copper metal. 
     The resistor pad  44  may be designed as a 40 ohm resistor, with approximately 0.3-0.5 amperes of current sufficient to melt the fusible line  60 . The resistor pad  44  may be approximately sized at 0.092 inch length by 0.25 inch. The fusible line may be tensioned within a range of 4 to 15 pounds in the described embodiment, for example 11 pounds. Under noted voltage and current targets, the resistor pad  44  will reach at least 250° C. in ambient air, and a presumably higher temperature in a vacuum or space environment. 
     Method 
     A method of making an electrothermal deployment system for deploying an apparatus secured by a fusible line to a nanosat may include the steps of providing a resistive element to form a substrate, securing the resistive element to the nanosat, and depositing an insulative material on a peripheral surface of the resistive element. The method may further include depositing a layer of electroconductive material over portions of the insulative material, providing an electrical source within the nanosat, and connecting the electroconductive material to the electrical source. 
     The method may further include stringing a fusible line over the electroconductive material, and securing the fusible line to the nanosat, then attaching the fusible line under tension to the apparatus to be released, and providing an electrical current from the electrical source through the fusible line sufficient to heat the fusible line to melting point for release of the deployable apparatus. 
     The method may further include laser etching the electroconductive material to form a resistor, and providing an electric current from the electric source through the resistor sufficient to heat the fusible line to its melting point. 
     Alternative Embodiments 
       FIGS. 5A, 5B, and 5C  display second, third, and fourth alternate embodiments of the electrothermal deployment system of the present disclosure. 
     For example,  FIG. 5A  displays a second embodiment of a deployment device  140 , which includes a resistive element  142  formed of a straight solid cylindrical substrate body  146 , as depicted. However, the fusible line  160  of the deployment device  140  passes through a U-clamp line guide  180 . 
     In  FIG. 5B , a third embodiment of a deployment device  240  depicts a tubular shaped resistive element  242  that has a C-shaped curved substrate body  246 . The fusible line  260  passes through a U-clamp line guide  280 . 
     Finally,  FIG. 5C  depicts yet a fourth embodiment of a deployment device  340 , that includes a resistive element  342  having a solid Chevron-shaped substrate body  346 . The fusible line  360  passes through a U-clamp line guide  380 . 
     The various substrate bodies  46 ,  146 ,  246  and  346  may be formed of lightweight metal, for example, an aluminum alloy. Dielectric as well as conductive coatings may be selectively applied over the alloy substrate bodies, and various portions of the coatings may then be laser etched, or otherwise selectively removed in predetermined places for desired results, consistent with printed circuit board practices. 
     Although several embodiments have been disclosed herein, it should be appreciated that the depictions shown and detailed with respect to various aspects and features are not intended to be limiting, but are for economy and convenience of description, only. For example, although the fusible line  60 ,  160 ,  260 ,  360  shown and described herein is a single strand line, i.e. the described monofilament, such fusible line may also be multi-stranded; i.e. having two, three, or more strands (not shown). Such strands could be braided or otherwise cross-linked in some fashion.