Abstract:
A controlled corrosion release system for a payload is provided. The payload is submerged in a conductive medium, such as seawater. The system includes clips which restrain the payload against a housing. A circuit is established to allow electrical current to flow from a power source contained within the housing, through the clips which serve as anodes, through the seawater, into the housing which serves as a cathode, and back to the power source. Accordingly, the clips corrode and weaken structurally. The clips eventually fail and the payload is released. The time for release is proportional to the power supplied, such that the release time can be controlled.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to release systems. More particularly, the present invention relates to controlled corrosion release systems for underwater payloads. 
     (2) Description of the Prior Art 
     A number of applications require the placement of a payload in an underwater environment. Typically, the payload is buoyant and is attached to an anchor that holds the payload underwater. After a period of time, the payload is released from the anchor and rises to the surface. The well-known options for securing and subsequently releasing the payloads from the anchor in these applications include constant corrosion releases, mechanical releases utilizing a motor/actuator, or burn wire releases. 
     A constant corrosion release starts corroding the moment it is emplaced. Therefore, with this method the actual moment of release cannot be changed. Also, the mechanical strength of the restraining member that forms the release will necessarily decrease, as this restraining member must also be the corroding member. Additionally, the corrosion release cannot be guaranteed to release when desired. 
     A mechanical release requires more volume for an actuator and more complexity and cost. This type of release will have a lower reliability and does not have an efficient or practical fail-safe release feature should the mechanical release fail to operate. A burn-wire release burns through a tensioned wire, releasing the pay load item. This method requires a more complex mechanism overall and has limited holding strength. As in the case of a mechanical release, a burn wire release does not have a fail-safe release feature. If the mechanism for initiating the burn-wire fails, the payload will not be released. 
     Thus, a need has been recognized in the state of the art to provide a release mechanism that reduces both complexity and costs, while increasing reliability. There is also a need to provide a release mechanism that includes a fail-safe feature, i.e., the release mechanism should eventually release the payload regardless if the primary release mechanism fails. 
     As in the case of a mechanical or burn-wire release, the payloads need to be released within a predetermined time after the release command is issued. Additionally, there is a need to provide a release mechanism that requires a small amount of volume to implement, while being able to vary the holding strength of the mechanism. 
     SUMMARY OF THE INVENTION 
     It is therefore a general purpose and primary object of the present invention to provide a controlled corrosion release system for a payload submerged in a conductive medium, such as seawater. The system includes one or more clips, which restrain the payload against a housing. A majority of the clips are anodes and the housing serves as a cathode. A power source is contained within the housing and is wired to the anodes and cathode. 
     When a release command is given, electrical current passes from the power source, through the anodes, into the medium and to the cathode. The anodes are oxidized in the solution, with the ions formed in the process being deposited on the cathode. Accordingly, the anodes erode and dissolve and weaken structurally. The anodes eventually fail and the payload is released. Typically, the payload is positively or negatively buoyant and the buoyant force of the payload accelerates the failure of the anodes as they weaken. The time for release is proportional to the power supplied, such that the release time can be controlled. 
     The system provides a simple and reliable means for releasing a payload. There are no complex mechanical linkages that are subject to corrosion and failure. Additionally, the system provides a fail-safe mechanism in that the anodes corrode over time even when no current is applied between the anodes and the cathode. 
     In one embodiment, a payload release system includes a housing, one or more clips attached to the housing, and a retaining ring secured to the clips. The payload is secured to the retaining ring and the housing maintains the payload submerged in a medium. 
     The system also includes a power source contained within the housing. A positive terminal of the power source is connected to a majority of the clips and a negative terminal of the power source is connected to the housing. The power source, the connected clips, the medium and the housing form a circuit. A controller is disposed within the circuit, wherein corrosion of the connected clips is proportional to a current modulated by the controller and flowing in the circuit. 
     In one embodiment, the clips connected to the power source are, in the absence of the medium, electrically isolated from the housing. Corrosion of the connected clips is confined to an end portion of each of the clips that abut the retaining ring. The end portion overlaps the retaining ring so as to resist the buoyancy of the payload. The end portion can have a sloped face, which abuts a complementary sloped face of the retaining ring. 
     In one embodiment, the housing can include a body portion to which the clips are attached. The housing also includes a lid. The power source is contained within a cavity formed between the body portion and the lid. The lid is sealed against the body portion and sealed against intrusion of the medium into the cavity. 
     In one embodiment, each of the connected clips includes a connection element attached to the clip and penetrating through the body portion into the cavity to connect to the positive terminal. An insulating layer can be secured between each connected clip and the body portion. 
     In one embodiment, a controlled corrosion payload release system includes a housing having a negative buoyancy, and one or more clips attached to the housing. The payload is secured to the clips and the housing maintains the payload submerged in a medium. A power source is contained within the housing. 
     A positive terminal of the power source is connected to a majority of the clips and a negative terminal of the power source is connected to the housing. In the absence of the medium, the clips connected to the power source are electrically isolated from the housing. The system also includes a controller, wherein corrosion of the connected clips is proportional to a current modulated by the controller. The current flows from the positive terminal to the connected clips, through the medium, to the housing and returns to the negative terminal. 
     In one embodiment, the housing includes a body portion, with the clips being attached to the body portion. The housing also includes a lid. The power source is contained within a cavity formed between the body portion and the lid. The lid is sealed against the body portion and sealed against intrusion of the medium into the cavity. 
     In one embodiment, each of the connected clips includes a connection element attached to the clip. The connection element penetrates through the body portion into the cavity to connect to the positive terminal. The clips include an end portion having a sloped face that overlaps a complementary sloped face of the payload so as to resist the buoyant force of the payload. The corrosion of the connected clips can be confined to their respective end portions. 
     In one embodiment, the system includes an insulating layer secured between each of the connected clips and the body portion. The system can also include a first seal about the connection element and disposed between each connected clip and the insulating layer, and a second seal about the connection element and disposed between the insulating layer and the body portion. The first and second seals prevent intrusion of the medium about the connection elements and into the cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein like reference numerals and symbols designate identical or corresponding parts throughout the several views and wherein: 
         FIG. 1  illustrates a schematic side view of a controlled corrosion release system; 
         FIG. 2  illustrates a schematic top view of a controlled corrosion release system; 
         FIG. 3  illustrates a cross-sectional view of the release system of  FIG. 2 , taken at line  3 - 3  of  FIG. 2 ; 
         FIG. 4  illustrates a schematic wiring diagram of the system of  FIG. 1 ; and 
         FIG. 5  illustrates a detailed view of a clip for the system of  FIG. 1 , taken at area A of  FIG. 3 ; 
         FIG. 6  illustrates a schematic side view of an alternate embodiment of a controlled corrosion release system having a buoyant housing and negatively buoyant payload. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , there is shown a schematic side view of controlled corrosion release system  10  deployed within conductive medium  2 , such as seawater. In the illustrated embodiment, payload  4  is buoyant and housing  14  is negatively buoyant and capable of holding payload  4  submerged in medium  2 . Thus, when payload  4  is released, it will rise to the surface of the sea for easy recovery. However, it should be understood that payload  4  need not be buoyant and housing  14  need not be negatively buoyant to remain within the scope of the present invention. For example, payload  4  and/or housing  14  may be positively, negatively, or neutrally buoyant without departing from the scope of the invention, as discussed later hereinbelow. 
     In the preferred embodiment illustrated in  FIG. 1 , buoyant payload  4  (shown dashed in  FIG. 1 ) is attached to retaining ring  12 . As will be described in further detail hereinafter, retaining ring  12  is secured against housing  14 . Housing  14  is weighted such that system  10  together with payload  4  is negatively buoyant and rests on bottom  6  of medium  2 . 
     Referring now to  FIG. 2 , there is shown a schematic top view of controlled corrosion release system  10 . Retaining ring  12  is secured against housing  14  by clips  16 . Referring also to  FIG. 3 , there is shown a partial cross-sectional view of system  10 , taken at line  3 - 3  of  FIG. 2 . For clarity of illustration, but not limitation, payload  4  is not shown in  FIGS. 2 and 3 . In  FIGS. 1 ,  2  and  3 , clips  16  are illustrated as being recessed into cutouts  14   a  of housing  14 . 
     Power module  18  is fixed within body  14   b  of housing  14 . Lid  14   c  of housing  14  attaches to body  14   b  and, with o-ring  20 , forms a watertight seal against body  14   b . Conductive rod  22  is attached to clip  16  and penetrates through body  14   b  into cavity  14   d  formed between body  14   b  and lid  14   c . Wiring  24  connects clip  16  to positive terminal  18   a  of power module  18  via conductive rod  22 . 
     Current flows from module  18 , through wiring  24 , into rod  22  and to clip  16 . Current flows from clip  16  through medium  2  surrounding system  10  to body  14   b  and returns to negative terminal  18   b  of module  18  via connection  26 . Thus, clip  16  serves as an anode and body  14   b  serves as a cathode in the circuit. Accordingly, and in the manner known in the art, clip  16  is oxidized and corrodes in conductive medium  2  when current flows as described hereinbefore. When clip  16  is sufficiently corroded, retaining ring  12  is released. In an exemplary embodiment, the anode (i.e., clip  16 ) is comprised of aluminum and the cathode (i.e., body  14   b ) is comprised of stainless steel. 
     In order for current to flow through medium  2  from anode clip  16  and then to cathode body  14   b , clip  16  must be electrically isolated from direct contact with body  14   b . Accordingly first insulating material  28  is placed between clip  16  and body  14   b . O-rings  30  prevent intrusion of medium  2  into cavity  14   d  adjacent rod  22 . 
     Additionally, second insulating material  32  surrounds fasteners  34 , which attach clip  16  to body  14   b . Further, third insulating material  36  surrounds rod  22  as it penetrates through body  14   b . To prevent unintended corrosion of retaining ring  12 , face  12   a  of retaining ring  12 , which abuts clip  12 , is formed of an insulating material. 
     Referring to  FIG. 4 , there is shown a schematic wiring diagram of circuit  100  formed by module  18 , wiring  24 , rod  22 , clip  16 , medium  2 , body  14   b  and connection  26 . In addition to power source  18   c , module  18  includes controller  18   d  in communication with an operator (not shown). When the operator provides a release signal to controller  18   d , controller  18   d  initiates the current flow described hereinbefore, in the direction illustrated by arrows C in  FIG. 4 . 
     As is known to those of skill in the art, the time for release depends on a number of factors, including, but not limited to, the power supplied, the surface area of clip  16  exposed to medium  2 , the quantity of material that needs to be corroded to effect the release, and the buoyancy of payload  4 . These factors can be controlled such that the time for release can be determined for a specific design. 
     Referring now to  FIG. 5 , there is shown a detailed view of retaining ring  12  and end portion  16   a  of clip  16 , taken at area A of  FIG. 3 . For clarity of illustration, cross-hatching is omitted from  FIG. 5 . Face  12   a  of retaining ring  12  is sloped such that top edge  12   b  has a greater interior radius than lower edge  12   c . End portion  16   a  of clip  16  has a slope complementary to that of face  12   a , such that retaining ring  12  closely abuts clip  16 . 
     The power required to corrode clip  16  depends on the surface area of clip  16  exposed to medium  2 . To reduce the power required to release retaining ring  12 , corrosion of clip  16  can be concentrated at end portion  16   a . To that end, non-conductive coating  16   b  is applied to clip  16  except at end portion  16   a.    
     When the release signal is given, current flows and end portion  16   a  begins to corrode. As end portion  16   a  corrodes, the strength of end portion  16   a  holding payload  4  against a separation force, or buoyant force, F of payload  4  is diminished. After the determined or designed release time period, the strength is no longer adequate to resist force F and retaining ring  12  and payload  4  are released. 
     Obviously many modifications and variations of the present invention may become apparent in light of the above teachings. For example,  FIG. 2  illustrates three clips  16  holding retaining ring  12 . The number of clips  16  can be varied to accommodate the design of payload  4  and as few as one clip could be used, where appropriate. Note that the power required to corrode anode clips  16  increases with an increasing number of clips  16 . 
     To lessen the power requirements for the configuration of  FIG. 2 , not all clips  16  need to function as anodes. For example, in the illustrated example using three clips, only two of the three clips  16  need to corrode to effectively release payload  4 . Buoyant force F can provide sufficient lifting force such that face  12   a  of retaining ring  12  can slide up end portion  16   a  of non-corroding clip  16 . Various means can be taken to ensure that one such clip  16  is non-corroding, including, but not limited to, not providing power to non-corroding clip  16 , or fully covering non-corroding clip  16  with non-conductive coating  16   b.    
     Additionally, face  12   a  of retaining ring  12  is described with respect to  FIG. 3  as being formed of insulating material. Those of skill in the art will recognize that retaining ring  12  itself can be formed of an insulating material, without the need for having its face  12   a  formed of a separate insulating material. Similarly, fasteners  34  may also be formed of an insulating material, without the need for separate second insulating material  32 . Further, insulating coatings can be used on rod  22  and fasteners  34  in lieu of third insulating material  36  and second insulating material  32 , respectively. 
     In a further alternate configuration, clips  16  need not be recessed in cutouts  14   a . Also, clips  16  can be fabricated with slotted bores therethrough for fasteners  34 . With this configuration, clips  16  can be radially adjusted to firmly abut against face  12   a  of retaining ring  12 . Still further, controller  18   d  can be in communication with payload  4  to receive the release command. Additionally, the shape of housing  14  can vary from the round or frustoconical shape illustrated in  FIGS. 1-4 . 
     In another embodiment, payload  4  and retaining ring  12  can be separated from housing  14  by a separation force other than buoyant force F. For example, payload  4  can be negatively buoyant and housing  14  can be positively buoyant to maintain payload at the surface  60  of the sea, as illustrated in  FIG. 6 . Thus, when clips  16  corrode and no longer have the strength to resist the force W caused by the negative buoyancy of payload  4 , payload  4  and retaining ring  12  are released and allowed to sink to the seafloor. 
     It will be understood that many additional changes in details, materials, steps, and arrangements of parts which have been described herein and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.