Abstract:
A shield comprised of carbon nanotube materials is used to provide a level of protection to a spacecraft. Shield segments are produced in a facility in space. The segments are transported from the facility to a vicinity of a spacecraft hull. The segments are assembled over the hull to substantially cover an area of the hull.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to shields for use with a deployed spacecraft. In particular, this application addresses the use of carbon nanotubes in a spacecraft shield configuration. 
     BACKGROUND OF THE INVENTION 
     Missions in space face the problem of spacecrafts being bombarded with space debris including meteoroids ranging in size from microscopic particles to visibly larger compositions. Compounding this problem is the case where the debris is traveling at high velocities. 
     Some high velocity debris can penetrate a traditional hard shelled spacecraft or cause a great deal of impact damage that weakens the shell of the craft making the shell more susceptible to subsequent failure. In the case of a penetration of the hull, this can lead to loss of a habitable pressurized environment that can endanger a crew. The debris could also impact sensitive equipment in a spacecraft, which could cause a variety of failures. 
     One solution to this problem has been the application of impact shields disposed about the outer surface of a spacecraft. There are a variety of techniques used including monolithic shielding. Monolithic shielding is typically a hard structure that is designed to prevent the debris from penetrating the shield. These types of shield cover a wide range of materials including metal coverings on the outside of a spacecraft. 
     Naturally, a solid metal shield—like steel—would be very heavy for a large spacecraft and that translates into a great deal of expense to place such a shield into orbit. This can be particularly true where the spacecraft has a complex geometry. 
     Carbon nanotubes have a higher strength than steel and yet are lighter. The carbon nanotubes are presently grown in a laboratory environment with the lengths of the tubes being relatively short. What is needed is a spacecraft shield that is comprised of carbon nanotubes of a longer length. 
     SUMMARY OF THE INVENTION 
     A method of producing a shield for use with a spacecraft to provide some protection to the spacecraft&#39;s hull against space debris is disclosed. A facility is placed in space to grow carbon nanotubes in a low gravity environment. The nanotubes are grown to form a segment of a spacecraft shield. The shield is then attached to the outer surface of a spacecraft&#39;s hull. Multiple shields are arranged to substantially enclosing the outer surface of the spacecraft&#39;s hull. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is generally shown by way of reference to the accompanying drawings in which: 
         FIG. 1  is a side view of a portion of a carbon nanotube. 
         FIG. 2  is a side view of a facility in orbit around the Earth. 
         FIG. 3  is a perspective view of a CNT shield segment. 
         FIG. 4  is a cut away side view of an embodiment of CNT shields disposed over a spacecraft&#39;s hull. 
         FIG. 5  is a cut away side view of another embodiment of CNT shields disposed over a spacecraft&#39;s hull. 
         FIG. 6  is a cut away side view of an embodiment of CNT shields disposed over a spacecraft&#39;s hull. 
         FIG. 7  is a perspective view of several CNT shield segments assembled. 
         FIG. 8  is a cut away side view of another embodiment of CNT shields using a hook type connector. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One aspect of the present invention is the use of carbon nanotubes (CNTs) as a bumper in a spacecraft shield for a Whipple type configuration. CNTs are cylindrical in shape and can have a length-to-diameter ration of up to approximately 132,000,000:1. 
     CNTs also have a strength between 10-60 GPa (gigapascals), which is much higher than steel. Even so, the specific density of CNTs is between 1.3-2 while steel is 7.8 making CTNs attractive for space deployment. CNTs can take numerous shapes such as single walled or multi-walled. 
       FIG. 1  identifies the general structure of a CNT  10 , which is comprised of carbon atoms  12  bonded together.  FIG. 2  identifies a space deployed facility  14  for producing carbon nanotubes. The facility  14  can be a spacecraft suitable for human habitation. In the embodiment identified, the facility  14  is an inflatable spacecraft for human use. In this figure, the spacecraft  14  is in orbit about the Earth. 
     The carbon nanotubes can be grown by techniques such as arc discharge, chemical vapor deposition, and laser ablation. The facility in space is situated in a low gravity environment. Low gravity also includes the case of zero gravity. The low gravity allows for growing longer CNTs. The CNTs can be combined with other compounds to form mixtures that can be tailored to specific operational and environmental requirements for shield segments. Such compounds can include plastics, polymers, other carbon based compounds such as Buckminsterfullerenes, or a combination of these materials or other appropriate materials. Growing techniques combined with bonding, the inclusion of other compounds, and the low gravity environment allows for the production of CNT shield segments of a wide variety of geometries. 
     In one embodiment this can be demonstrated by producing a surface that is more desirable for bonding two shield segments together with, for example, an adhesive. In other embodiments, the shield segments can include holes for receiving bolts in securing the shield segment to a spacecraft. 
     The facility can be a separate structure from a spacecraft to receive the shielding, or can be the spacecraft. By having the operation of producing the carbon nanotubes as part of the spacecraft, the logistics of transporting the completed shielding can be less complicated. 
       FIG. 3  identifies a shield segment  16  comprised of CNTs. The CNTs can be formed in shield segment shapes such as embodied in  FIG. 3 .  FIG. 4  identifies one embodiment of the shield segments attached to the hull of a spacecraft. The shield segment  16  is substantially the shape of a corresponding section of the hull  20  in that the shield segment  16  is set away from the hull  20  and therefore not necessarily the exact shape of the hull  20 . The shield segment  16  is attached to the external spacecraft hull in space  18 . The Hull  20  can be a solid hull or a flexible hull as found in an inflatable spacecraft. In the present embodiment, a skeletal structure  22  surrounds the hull  20 . The skeletal structure  22  has a plurality of connection points  24  to receive connecting pins  26 . The shield segments  16  are placed in contact with the skeletal structure  22 . The connecting pins  26  are secured to the connecting points  24  thereby holding the segments  16  in place. 
       FIG. 5  identifies another embodiment for securing the shield segments to the hull of a spacecraft. In this embodiment, the shield segments are secured one to another using adhesive. Adhesive  27  is used to secure the shield segments to the hull  20 . In another embodiment, an intermediate layer could be placed on the hull to receive the adhesive. The adhesive holds the segments  16  in place and other segments  16  are mounted on top. This procedure could be repeated until a desired lever of layering is achieved. 
       FIG. 6  is another embodiment that uses adhesives to secure the shield segments together. In this embodiment the shield segments  16  are formed to partially overlap. Adhesives  27  secure the overlapping portions of the segments together. In this way, the segments  16  do not generally contact the hull  20 . However, in other embodiments the segments  16  can be in contact with the hull while lacking an adhesive between the segment and the hull. 
     In  FIG. 7 , an inhabitable inflatable spacecraft  28  is deployed in space. Inside the spacecraft  28 , equipment produces CNT spacecraft shield segments. In this embodiment, shield segments  30  are transported outside the spacecraft  28  and assembled into larger segments  32  that can then be placed over an area of the spacecraft  28 . This embodiment also illustrates the use of shield segments of different shapes to accommodate the outer hull geometry of a spacecraft. In other embodiments the shield segments can individually be placed over the outer hull of a spacecraft. 
       FIG. 8  identifies a CNT spacecraft shield arrangement with a receiving CNT shield  34  having holes  36  to receive a hook type structure  38  that is part of a retaining CNT shield  40 . A variety of geometries for the holes and hook type structures could be used and the invention does not limit such a variety. 
     While embodiments have been described in detail, it should be appreciated that various modifications and/or variations may be made without departing from the scope or spirit of the invention. In this regard it is important to note that practicing the invention is not limited to the applications described herein. Many other applications and/or alterations may be utilized provided that such other applications and/or alterations do not depart from the intended purpose of the invention. Also, features illustrated or described as part of one embodiment may be used in another embodiment to provide yet another embodiment such that the features are not limited to the embodiments described herein. Thus, it is intended that the invention cover all such embodiments and variations. Nothing in this disclosure is intended to limit the scope of the invention in any way.