Abstract:
A deployable/retractable expandable bag system for enclosure and release of space objects, constructed from materials exhibiting abrasion resistance and ballistic protection. Pressurized expandable textile trusses support textile membrane materials exhibiting radial contracting or collapsing contracting directional qualities. Stabilizing wires define bag length and minimize rotational forces of the captured object. Upon entry of the space object into the bag system, pressurized gas in trusses is released. The expandable trusses and membranes retract over and onto the space object. The expandable bag may be re-pressurized, and the bag re-opened, for removal and redirection of the space object; upon re-stowing, the system is ready for another capture mission.

Description:
FIELD OF THE INVENTION 
     The invention relates to an expandable, deployable and retractable bag system for capture of space-based objects for transfer or projection along new trajectories. More particularly, the present invention relates to a compact, low mass apparatus constructed from flexible and expandable truss structures, textiles, and pressure hoses that each flex and extend along specified, differing axes to effectively not only capture, but also pull in space objects for maximum control. 
     BACKGROUND OF THE INVENTION 
     In response to the relatively small meteor which broke up near Chelyabinsk, Russia in February 2013 and ongoing investigation of Near Earth Object (NEO) close encounters with earth which could seriously impact life on earth, the U.S. Congress has issued a mandate to the National Aeronautics and Space Administration (NASA) to protect planet Earth. NASA has since issued a Grand Challenge to capture an asteroid, or remove a boulder on a larger asteroid, and return samples to earth in about 2025. 
     The United Nations also has an international task force to investigate an asteroid re-direct demonstration project, currently planned for 2023. Several businesses are planning to mine asteroids in space. To optimally mine the asteroids, the asteroids may need to be transferred to other locations in space such as the earth-moon Lagrange Point L1 or into an orbit around the moon. 
     Man-made space-object debris is an additional concern. An estimated 4.4 million pounds of space-object debris are in low-earth orbit. These space objects can be catastrophic for humans and spacecraft. The International Space Station dodges man-made space-object debris each year. 
     Expandable capture bag concepts to capture an asteroid or other space objects have been promoted by NASA and various private enterprises. While these prior art expandable bags can be stowed somewhat compactly and deployed to a larger size to contain a space object, they typically are constructed from non-expandable/non-stretchable textiles impregnated with an elastomer to form a pressure barrier to contain the pressurized gas. 
     Expandable/stretchable textile fibers are similar to a coiled spring. The fibers uncoil under tension, and then return to their coiled configuration when the tension is removed. Expandable/stretchable textiles are difficult to impregnate with an elastomer and still allow the textile to expand or stretch. When an elastomer is impregnated into an expandable textile, the elastomer prevents the textile fibers from uncoiling. The result is that the textile becomes essentially non-expandable and non-stretchable. 
     Prior art capture bag systems utilize non-stretchable pressurization (hose/tube) systems because the impregnated elastomer restricts the textiles&#39; ability to stretch and expand. Consequently, the entire deployed length of the hose or tube must be stowed. The result is a system having a large stowed volume and a relatively high mass. 
     In addition, the prior art capture bag systems deploy to a large diameter and block sensors onboard the spacecraft used to identify and accurately locate a space object. 
     Accordingly, there is an as of yet unmet need in the art for a space-object capture apparatus that: 1) is made of components that may be compactly stowed at a size and length significantly less than when deployed; 2) is made of components having a lower combined mass than prior art systems; 3) maintains an adequate pressurized gas barrier without components constructed from non-expandable elastomer-impregnated materials; 4) is constructed using materials that are simultaneously expandable, stretchable, abrasion resistant, and impervious to ballistics; and, 5) upon deployment, continues to allow spacecraft sensors to operate and operators to view space from within the apparatus. 
     THE INVENTION 
     Summary of the Invention 
     The inventive Stretch Skin Receptacle for Space Object Capture and Release of this application comprises an expandable, deployable space object capture and release apparatus for mounting to a spacecraft vehicle, the apparatus deployable from a folded compact stowed position into a bag shape deployed position. 
     The apparatus comprises: 
     1) a plurality of truss assemblies, each of the truss assemblies constructed from a flexible, expandable, filament-reinforced generally tubular shaped material. The truss assemblies have a stowed non-pressurized length, a stowed non-pressurized diameter, a deployed pressurized length, a deployed pressurized diameter, and a deployed generally hexagonal ringed shape; 
     2) a bag attachment assembly of a diameter less than the deployed pressurized diameter of the truss assemblies. The bag attachment assembly is capable of secure attachment of the apparatus to the spacecraft vehicle; 
     3) a plurality of collapsing membranes generally spanning from the bag attachment assembly at a first end proximate the space vehicle, to a first truss assembly at a second distal end. The collapsing membrane is constructed from a material capable of expansion and retraction in a primary longitudinal direction; 
     4) a plurality of stretch skin clenching membranes generally spanning from the first truss assembly to an end distal truss assembly, the stretch skin membranes constructed from a material capable of expansion and retraction in a primary radial direction; 
     5) a plurality of external pressure hose assemblies constructed from hollow collapsible and flexible conduit materials, the hose assemblies in operative combination with the truss assemblies and capable of retaining and transporting a pressurized gas to each of the truss assemblies and capable of operating in a space environment; 
     6) a protective cover on the bag attachment assembly. The cover opens upon a release of the pressurized gas for a deployment of the truss assemblies into the deployed position; and, 
     7) at least one pressurized gas container in operative combination with the external pressure hose assemblies upon the deployment of the apparatus. 
     Each of the truss assemblies, collapsing membranes, stretch skin membranes and external pressure hose assemblies is defined by a respective stowed non-pressurized length and diameter that is at least one half the size of a corresponding deployed pressurized length and diameter. 
     A method of capturing a space object of interest located in earth-moon orbit or beyond earth-moon orbit comprises the operations of: 1) providing the receptacle as described above; 2) releasing the space vehicle with attached apparatus into earth-moon orbit; 3) maneuvering the space vehicle with attached apparatus to an orbit corresponding to an orbit for the space object of interest; 4) deploying the apparatus to the deployed position; 5) surrounding the space object of interest with the apparatus; 6) retracting the apparatus to the stowed position, thereby: a) causing the stretch skin membranes to retract radially around the space object to retain the space object within the apparatus; and, b) causing the collapsing membranes to retract longitudinally, pulling the space object towards the space vehicle; and, 7) manipulating the space object of interest. 
     The manipulating step of the method includes: retaining the space object within the apparatus, mining the space object, mining and releasing the space object, scientific examination of the space object, scientific examination and release of the space object, geological examination of the space object, geological examination and release of the space object, movement of the space object to a new orbit further away from earth, movement of the space object to a new orbit further away from earth and release of the space object, movement of the space object towards the earth&#39;s surface, movement of the space object towards the earth&#39;s surface and release of the space object, release of the space object, deploying the apparatus to release the space object, and, deploying the apparatus to release the space object and stowing the apparatus for future missions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail with reference to the attached drawings, in which: 
         FIG. 1  is isometric perspective view drawing of a spacecraft with a prior art stowed expandable asteroid capture bag in a stowed configuration; 
         FIG. 2  is an isometric perspective view drawing of a spacecraft with a prior art expandable asteroid capture bag in a deployed configuration; 
         FIG. 3  is an isometric perspective view drawing of a spacecraft with a prior art expandable asteroid capture bag loosely collapsing around a space object after the gas in the expandable bag has been removed; 
         FIG. 4  is a top view perspective drawing of the inventive Stretch Skin Receptacle for Space Object Capture and Release of this application in a stowed position; 
         FIG. 5  is a top view perspective drawing of the inventive Stretch Skin Receptacle for Space Object Capture and Release of this application in a deployed position; 
         FIG. 6  is a side view drawing of the inventive Stretch Skin Receptacle for Space Object Capture and Release of this application in a deployed position; 
         FIGS. 7A-7C  are isometric view drawings of the Stretch Skin Receptacle for Space Object Capture and Release in a deployed position approaching, surrounding, and retaining a space object; 
         FIG. 8  is a side elevation view drawing of the Stretch Skin Receptacle for Space Object Capture and Release in a deployed position showing a retained space object in transport to a different trajectory; 
         FIG. 9  is a side elevation view drawing of the Stretch Skin Receptacle for Space Object Capture and Release in a re-pressurized and re-opened position with space object still positioned within the apparatus; 
         FIG. 10  is a side elevation view drawing of the Stretch Skin Receptacle for Space Object Capture and Release in a re-pressurized and re-opened position backing away from a space object being released; and, 
         FIG. 11  is a side elevation view drawing of the Stretch Skin Receptacle for Space Object Capture and Release in a self-retracted stowed position ready for another mission. 
     
    
    
     DETAILED DESCRIPTION 
     In general terms, this application discloses a truly stowable and expandable capture bag system for repeated use and effective capture of space objects given a construction entirely out of two types of expandable materials: one material that wraps around the object, and another material which simultaneously pulls the object in closer to the space vehicle for controlled movement. 
     The apparatus can expand to two or three times its stowed length, and the system is one-third to one-half the mass and stowed volume compared to prior art expandable bag systems. As a result, the apparatus may be launched at a significantly lower cost. 
     The system utilizes a stretchable/extendable pressure hose system to pressurize expandable trusses. The pressure hose system comprises space-object protection materials. Current stretchable/extendable pressure hoses cannot survive the space-object debris and other space environments. 
     Once the space object is in the expandable bag, the pressure in the tubes/trusses is removed. The expandable material system begins to retract, capturing the space object within the bag. The expandable bag can be re-pressurized and the bag re-opened to remove and redirect the space object. 
       FIG. 1  shows a space vehicle  1  floating in space with a prior art stowed asteroid capture bag  3  in a stowed (non-deployed) configuration. Solar arrays  2  on either side of the vehicle  1  provide power to the space craft  1  and bag system  3 . 
       FIG. 2  shows the prior art bag system  3  of  FIG. 1  in a deployed position  4 . Referring to  FIG. 2 , the deployed bag system  4  expands into space via pressurized gas (not shown) carried through a series of pressure hoses  5 . The sides of the pressurized bag system  4  form tori  6 . The tori  6  are constructed from layered materials forming generally ovoid, circular pockets to retain the pressurized gas. 
     Referring again to  FIG. 2 , a space object of interest  7  is shown being surrounded by the prior art deployed bag system  4 . As the spacecraft  1  approaches the object of interest  7 , the containment bag  3  shown in  FIG. 1  is deployed and opened, and the spacecraft  1  signals the expandable bag system  3  to pressurize the expandable bag into the deployed configuration  4 . The prior art pressure hoses  5 , made of conventional non-stretchable materials, are located around the periphery of the deployed bag. The hoses  5  also provide a restraint system for the inflated bag  4 . The prior art hoses  5  cannot withstand ballistic impacts, and are subject to bursting in response to impact forces. 
       FIG. 2  depicts five expandable tori  6  which are the primary expandable structure members for the expandable bag  4 . These tori  6  provide structural support for the bag  4  while also containing the space object  7  when it is in the bag  4 . Due to the nature of many space objects  7  as spinning or tumbling when captured, it is likely that the bag  4  must remain pressurized to provide a somewhat rigid structure until the spacecraft&#39;s  1  control system can overcome the inertia of the space object  7 . Thus, the pressurized bag  4  continues to provide an opening where the space object  7  could possibly be inadvertently ejected from the bag  4 , requiring another capture attempt by the spacecraft  1 . 
       FIG. 3  shows the prior art expandable bag  4  loosely collapsing around the space object  7  after the gas in the expandable bag  4  has been released. Referring to  FIGS. 2 and 3 , once the space object  7  is within the bag  4  and the spacecraft  1  has minimized the space object&#39;s  7  inertia forces, the gas is released from the tori  6  resulting in the bag  4  loosely collapsing around the space object  7  to capture it. The asteroid  7  may still have a tendency to move, since it is loosely constrained within the collapsed bag  4 , introducing additional and undesirable spacecraft  1  control complexities. 
       FIG. 4  shows a top view perspective of the inventive system in a stowed configuration  21  within a six-sided protective closure  8 . The protective closure  8  can be of any suitable or desired geometry, from circular, to a variety of multi-sided enclosures, depending on the geometry of the attached spacecraft  1  (shown in  FIGS. 1-3 ) and the available volume within a launch fairing. The protective closure  8  is attached to the base of the system  21 . A central region contains sensors  10  mounted to the spacecraft  1  (shown in  FIGS. 1-3 ) to provide an uninterrupted view of objects in space, both when the system is stowed  21  and when the system is deployed  9  (shown in  FIGS. 5-6 , infra). 
       FIG. 5  shows a top view perspective of the inventive system in a deployed, generally hexagonal, configuration  9 , with the viewer looking into the inflated bag  9 . The deployed configuration  9  could also be circular or a variety of multi-sided geometries. 
     Referring to  FIG. 5 , the central region contains sensors  10  mounted to the spacecraft  1  (shown in  FIGS. 1-3 ). As shown in  FIG. 5 , upon deployment, the spacecraft sensors  10  are not blocked by the deployed configuration  9 . The present invention is designed and fabricated to allow spacecraft sensors  10 , such as microwave and radar, to be centrally located interior of the stowed  21  and deployed  9  expandable bag. In addition, the bag attachment assembly  11  may further comprise an image capturing and transmission device capable of transmitting to an operator a view into space from a perspective inside the apparatus in the deployed position  9 . 
     Referring again to  FIG. 5 , quadrilateral shaped collapsible membrane panels  12  expand radially from the central region  10  outwards towards the first side-defining truss assembly  13 . External pressure hoses  14  carry the pressurized gas (not shown) to the truss assemblies  13  upon deployment. 
       FIG. 6  shows a side elevation view of the system in a deployed configuration  9 . As shown in  FIG. 6 , the deployed configuration  9  comprises three rows of expandable truss assemblies  13 . The number of rows of expandable truss assemblies  13  may vary, depending on the structural requirements to contain space objects  7  (shown in  FIGS. 1-3 ) of different shapes and lengths. 
     Referring to  FIG. 6 , stabilizing wires  15  assist in maintaining the bag geometry when a space object  7  (shown in  FIGS. 1-3 ), which may have some movement, is entering or within the expandable bag system  9 . The wires  15  minimize the rotational or tumbling forces of the captured space object  7 . The stabilizing wires  15  also assist in constraining the expandable bag system  9  to a desired axial length. 
     Referring to  FIG. 6 , the collapsing membrane panels  12  have their preferred fiber alignment oriented in the longitudinal direction of the system  9 . The collapsing membranes  12  extend upward from their compactly stowed configuration when tension is applied to the membranes  12 . When tension is removed from the membranes  12 , the membranes  12  return to their compactly stowed configuration. A portion of the collapsing membranes  12  may be wrapped around the bag attachment assembly  11 , on the one hand, and the first truss assembly  13 , on the other hand, and retained in position by a filament sewn through the membrane  12  at an area of overlapping membrane  12  materials. Alternately, the collapsing membranes  12  may be secured by any suitable or desired method, including, without limitation: sewing, co-curing, vulcanizing, and adhesive bonding. 
     Referring again to  FIG. 6 , a second set of membranes  16 , referred to herein as the clenching (or stretch skin) membranes  16 , form the upper side walls of the expandable bag system  9 . The circumferential clenching membranes  16  have their preferred fiber alignment oriented in the circumferential direction of the expandable bag system  9 . The clenching membranes  16  extend outward (radially) from their compactly stowed configuration when tension is applied to the membranes  16 . When tension is removed from the membranes  16 , the membranes  16  return to their compactly, more centrally-located stowed configuration  21 . The clenching membranes  16  may be secured to the truss assemblies  13  by any suitable or desired method, including without limitation: sewing, co-curing, vulcanizing, and adhesive bonding. 
     Referring again to  FIG. 6 , the pressure hoses  14  provide a hollow conduit for the passage of pressurized and de-pressurized gases to and from each truss assembly  13 .  FIG. 6  also depicts the protective cover  8  in its deployed (open) configuration, permitting deployment of the expandable bag system  9  as the pressure hoses  14  fill the expandable truss assemblies with a pressurized gas. The protective cover  8  may be constructed from rigid or flexible materials. 
     Referring again to  FIG. 6 , the expandable trusses  13  are fabricated from materials exhibiting abrasion resistance and ballistic protection. In general terms, the truss material comprises: 1) a protective, abrasion-resistant outer layer; and, 2) a textile-based inner layer having an elastomeric barrier applied to one surface to act as a pressure barrier for the gas retained within the truss, and a shear thickening fluid applied to the opposite surface for ballistic protection. 
     Referring again to  FIG. 6 , the truss  13  outer layer may be constructed primarily from a polytetrafluoroethylene (PTFE) compound. One or more PTFE layers may be utilized depending on the level of abrasion protection required. The PTFE materials are expandable, similar to Gortex™, to render them capable of stretching and retracting. The inner textile layer is constructed primarily from an aramid compound. The inner layer comprises a stretchable/expandable rugged material conventionally fabricated by braiding, weaving or knitting methods. The textile material exhibits good abrasion and ballistic impact resistance. Kevlar™, Vectran™, PBO™ and Nomex™ are examples. The inner layer has a top surface and an opposing bottom surface. The top surface of the inner layer proximate the outer layer is coated with a shear thickening fluid compound, and the bottom surface of the inner layer is coated with an elastomer compound. The inner layer is capable of a circumferential diameter enlargement in a radial direction of two to three times an original radius when the bottom surface coated with the elastomer is placed under a tension force. Conversely, the inner layer is capable of a self-retraction upon a removal of a tension force applied to the elastomer. 
     Referring again to  FIG. 6 , the truss construction provides for axial or circumferential expansion with minimal expansion in the longitudinal direction. Typical extension is two to three times the length of the textile when the tension is removed. Consequently, the expandable truss assemblies  13 , when pressurized, expand radially outward to two to three times the diameter of conventional expandable structures using non-stretchable/non-expandable textile/elastomeric materials. 
     It should be understood that any suitable or desired components of the expandable bag system  9 / 21  may be constructed using the material system utilized for the trusses  13  to provide sufficient ballistic protection. For example, the pressure hoses  14  may be constructed from a layered material system comprising: 1) a protective, abrasion-resistant outer layer; and, 2) a textile-based inner layer having an elastomeric barrier applied to one surface to act as a gas pressure barrier, and a shear thickening fluid applied to the opposite surface for ballistic protection. 
       FIGS. 7A through 7C  show the expandable bag system in a deployed position  9  maneuvering around a space object  7 , and securing the space object  7  in a collapsed position  17 . It should be understood that the space vehicle  1  is operable via satellite to earth communication systems (not shown) to move the deployed system  9  around the object of interest  7 . 
     Referring to  FIGS. 7A and 7B , as the spacecraft  1  closes in on a space object  7 , the expandable bag system is deployed  9 . The spacecraft  1  is maneuvered to capture the space object  7 . 
     Referring to  FIG. 7C , once the space object  7  is within the expandable bag system  9 , the pressure within the expandable bag system  9  is removed. The truss assemblies  13  are no longer in tension since the internal pressure has been removed. The clenching stretch skin membranes  16  coil back into their compact natural state. The truss assemblies  13  self-retract to their unpressurized length which reduces the circumferential opening of the now-collapsed expandable bag system  17 . When the truss assemblies  13  self-retract, the tension on the clenching membranes  16  is removed and the membranes  16  self-retract circumferentially inward. The expandable bag system  17  shrinks and conformably wraps around the space object  7 . The collapsing membranes  12  also have the tension removed. The collapsing membranes  12  self-retract downward towards where the membranes  12  are attached to the space vehicle  1 . The captured space object  7  is pulled closer to the spacecraft  1 . The space object  7  is more-closely coupled to the spacecraft  1 , improving the spacecraft&#39;s  1  ability to control the captured space object  7 . 
     Referring again to  FIGS. 1-3  and  6 - 7 C, unlike the expandable capture bag  4  of the prior art where the bag  4  closes loosely around the space object  7  as depicted in  FIG. 3 , the expandable bag system  17  securely captures the space object  7  due to the self-retracting characteristics of the truss assemblies  13 , the collapsing membranes  12 , and the clenching stretch skin membranes  16 . 
     In particular, as shown in  FIG. 3 , the prior art system loosely contains the space object  7  so that the spacecraft  1  and the object  7  act more like independent masses, thereby increasing the complexity of controlling the spacecraft  1 . In contrast, referring to  FIGS. 6 and 7C , by utilizing the expandable bag system  17  of the present invention, the stretch skin membranes  16  conform to the actual, unique shape of the space object  7 , and the space object  7  is more closely coupled to the space vehicle  1  by the contraction of the collapsible membrane panels  12 . 
       FIG. 8  shows the spacecraft  1  with the self-retracted expandable bag system  17  wrapped around the captured space object  7  and travelling forward along a line and in the direction of arrow  18  to prepare to redirect and release the space object  7  into a different trajectory. 
       FIG. 9  shows the expandable bag system in a re-pressurized and re-opened position  9 . The space object  7  is no longer constrained by the expandable bag system as shown in the collapsed position  17  in  FIG. 8 . The object  7  is floating within the opened bag system  9 . 
       FIG. 10  shows the spacecraft  1  in a reverse trajectory of momentum, as shown along the line and in the direction of arrow  19 . As the spacecraft  1  reverses position, the floating space object  7  continues its momentum along the direction of arrow  18 . 
       FIG. 11  shows the expandable bag system returned to a de-pressurized, re-stowed position  21  ready for its next space object capture mission. Note that throughout the entire stowed/deployed/re-stowed activities, the spacecraft sensors located proximate the central region of the bag system  10  have had an unrestricted view of the entire mission operation. 
     Referring to  FIGS. 1 , and  7 A through  11 , a method of capturing a space object of interest  7  located in earth-moon orbit may comprise the operations of: 1) providing the inventive apparatus  21  as disclosed herein; 2) releasing a space vehicle  1  with attached apparatus  21  into earth-moon orbit; 3) maneuvering the space vehicle  1  with attached apparatus  21  to an orbit corresponding to an orbit for the space object of interest  7 ; 4) deploying the apparatus to the deployed position  9 ; 5) surrounding the space object of interest  7  within the apparatus  9 ; 6) retracting the apparatus to the stowed position  17 , thereby causing the clenching membranes  16  to retract radially around the space object  7 , thereby retaining the space object  7  within the apparatus  17 , and causing the collapsing membranes  12  to retract longitudinally, thereby pulling the space object  7  inwards towards the space vehicle  1 . 
     Once the space object  7  is retained within the collapsed system  17 , the object  7  may be manipulated. The manipulating step may include: retaining the space object within the apparatus, mining the space object, mining and releasing the space object, scientific examination of the space object, scientific examination and release of the space object, geological examination of the space object, geological examination and release of the space object, movement of the space object to a new orbit further away from earth, movement of the space object to a new orbit further away from earth and release of the space object, movement of the space object towards the earth&#39;s surface, movement of the space object towards the earth&#39;s surface and release of the space object, release of the space object, deploying the apparatus to release the space object, and, deploying the apparatus to release the space object and stowing the apparatus for the next mission. 
     Referring again to  FIGS. 1 , and  7 A through  11 , the apparatus may also be utilized to capture an object, such as a boulder, from the surface of an asteroid. The method of capturing a boulder from the surface of an asteroid located in an earth-moon orbit comprises the operations of: 1) providing the inventive Stretch Skin Receptacle apparatus  21  as disclosed herein; 2) releasing a space vehicle  1  with attached apparatus  21  into earth-moon orbit; 3) maneuvering the space vehicle  1  with attached apparatus  21  to an orbit corresponding to an orbit for the asteroid; 4) deploying the apparatus to the deployed position  9 ; 5) surrounding a boulder  7  on the asteroid in the apparatus  9 ; 6) retracting the apparatus to the stowed position  17 , thereby causing the clenching membranes  16  to retract radially around the boulder  7 , thereby retaining the boulder  7  within the apparatus  17 , and causing the collapsing membranes  12  to retract longitudinally, thereby pulling the boulder  7  inwards towards the space vehicle  1 . 
     For both methods disclosed herein, once the object of interest  7  has been released, the apparatus may be re-configured to the stowed position  21  while the space vehicle  1  is moved in the direction of another object of interest  7 . 
     The inventive Stretch Skin Receptacle for Space Object Capture and Release of this application has wide applicability to the space industry, namely to provide a low-cost, re-usable, reliable, and controllable method for capturing and releasing space objects  7 . The inventive system  21  may be compactly stowed adjacent to the upper portion of a spacecraft  1 , while the spacecraft  1  is attached to a launch vehicle and also while the spacecraft  1  is travelling independently to the space-object of interest  7 . When the spacecraft  1  approaches a space-object of interest  7 , the expandable bag system  9  is pressurized via a pressurization system. The expandable/stretchable pressure hoses  14  pressurize the expandable trusses  13  via a pressurized gas canister  20 , and also provide the restraint system to contain the deployed bag  9  at a desired axial length from the base  11 . 
     It should be understood that various modifications within the scope of this invention can be made by one of ordinary skill in the art without departing from the spirit thereof and without undue experimentation. For example, the expandable bag capture system  21  may be designed, fabricated and assembled as a modular unit to facilitate removal of worn units from the spacecraft  1  and installation of new units by either humans or robotic spacecraft while in space. 
     The base structure  11  may feature quick-release mechanisms for the purpose of quickly, easily and reliably removing the expandable bag capture system from the spacecraft  1  while in space. In this embodiment, the base portion  11  of the expandable bag system  21  is not removed, only the bag portion itself at its structural interface to the base portion  11 . 
     Any suitable or desired pressurized gas vessel(s)  20  may be utilized. Ideally, the gas canisters  20  are of sufficient capacity to provide multiple deployments of the expandable bag capture system  9 . An optional accumulator system would allow the gas to be collected for reuse. 
     This invention is therefore to be defined as broadly as the prior art will permit, and in view of the specification if need be, including a full range of current and future equivalents thereof.