Abstract:
A vehicle launch system having an acoustic insulator, wherein the acoustic insulator is an inflatable assembly disposed between a shroud and a spacecraft vehicle and containing gaseous material for dampening the acoustic noise effect in a spacecraft vehicle ferrying cavity during the initial vehicle launch stages.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to vehicle launch systems, and more specifically to a vehicle launch system having an acoustic insulator for absorbing the acoustic energy generated during the initial stages of a space vehicle launch. 
     2. Description of the Prior Art 
     Traditionally, launchable spacecraft vehicles are enclosed in a protective shroud and mounted onto a high power launch vehicle which is used to propel the spacecraft vehicle into space. During the first three minutes of a launch, a significant amount of acoustic noise (or vibration) is generated at the launch vehicle, traveling up the sides of the spacecraft vehicle where it is conducted off the interior surface of the protective shroud. This conduction of the acoustic energy within the confined area between the spacecraft and the shroud causes the spacecraft components and electronics to be subjected to a high concentration of acoustic vibration. The acoustic vibration reaches levels that may cause structural damage to the spacecraft vehicle components and electronics. 
     Present launch systems use a variety of techniques to reduce the impact of acoustic vibration on the launchable spacecraft. One such technique requires spacecraft vehicle components that are structurally robust and have unique energy absorbing characteristics sufficient to survive extreme acoustic vibration. A second technique provides the use of a barrier between the source of the acoustic vibration and the spacecraft vehicle. The barrier is created by filling the area between the shroud and the spacecraft vehicle with a gaseous material that insulates the spacecraft from the extreme acoustic environment. However, each of the described conventional approaches has inherent drawbacks. 
     Regarding the first technique, building structurally robust components that are energy absorbent may require heavier components, special materials and additional design steps. As the overall weight of the spacecraft is increased, the amount of fuel required launching the spacecraft increases. Special energy absorbing materials and additional design steps further increase the spacecraft vehicle fabrication costs. 
     Regarding the second technique, creating a barrier from gaseous materials, typically helium, has been found to enable low voltage arcing within the electronic circuitry of the spacecraft vehicle. The low voltage arcing occurs when the unconfined gaseous material seeps into the electronic circuitry of the spacecraft. 
     Based on the techniques known in the art for reducing the acoustic vibration effect on launchable spacecraft vehicles, a vehicle launch system having an acoustic insulator which, maintains vehicle weight limitations, decreases overall launch costs and eliminates low voltage arcing effects is highly desirable. 
     SUMMARY OF THE INVENTION 
     It is an aspect of the present invention to provide a vehicle launch system having an acoustic insulator. Briefly, the vehicle launch system includes a spacecraft disposed on a launch vehicle where the launch vehicle has a means for launching the spacecraft. The vehicle launch system further includes a shroud extending from the launch vehicle forming a ferrying cavity whereby the shroud encloses the spacecraft. Disposed between the shroud and spacecraft is an inflatable, flexible element where the inflatable, flexible element contains a gaseous material having a means for dampening the acoustic vibration concentrated within the ferrying cavity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference is now made to the following specification and attached drawings, wherein: 
     FIG. 1 is an illustration of a vehicle launch system including an acoustic insulating balloon assembly in accordance with a preferred embodiment of the present invention; 
     FIG. 2 a  is an illustration of the elements of an acoustic insulating balloon subassembly in accordance with the preferred embodiment of the present invention; 
     FIG. 2 b  is an isometric illustration of an acoustic insulating balloon subassembly in accordance with the preferred embodiment of the present invention; 
     FIG. 2 c  is a front view illustration of an acoustic insulating balloon subassembly in accordance with the preferred embodiment of the present invention; 
     FIG. 2 d  is an illustration of an integral tear-cord configuration in accordance with the preferred embodiment of the present invention; 
     FIG. 2 e  is a front view illustration of a fully assembled acoustic insulating balloon subassembly in accordance with the preferred embodiment of the present invention; 
     FIG. 3 is an illustration of an acoustic insulating balloon assembly in accordance with the preferred embodiment of the present invention; 
     FIG. 4 is a top view illustration of an acoustic insulating balloon assembly in accordance with the preferred embodiment of the present invention; 
     FIG. 5 is a bottom view illustration of an acoustic insulating balloon assembly attached to vehicle launch system shroud in accordance with the preferred embodiment of the present invention; and 
     FIG. 6 is an illustration of an acoustic insulating balloon assembly collapsing from a spacecraft vehicle following the first stage of a launch sequence. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, the present invention relates to vehicle launch system  10  and, more particularly, to an acoustic insulating balloon assembly  12  located on the inside of a launch vehicle payload fairing  20 . The acoustic insulating balloon assembly  12  of the present invention is utilized to dampen the effects of acoustic energy (vibration) on a spacecraft  16  during the first three minutes of lift-off. The balloon assembly  12  is filled with a gaseous material and forms a confined volume around the spacecraft  16 . Insulating the spacecraft  16  with the balloon assembly  12  provides a contained barrier between the launch vehicle shroud  14  and the spacecraft  16  protecting the spacecraft  16  from the effects of high acoustic vibration. It is important to note that the present invention is not limited to space launch applications, but may also be utilized to dampen acoustic effects in missile and other applications having concentrated payload compartments on board. 
     Referring to FIGS. 2 a  through  2   e , an acoustic insulating balloon assembly  12  (see FIG. 1) is constructed from a plurality of subassemblies, further referenced herein as balloon subassemblies  22 . Each balloon subassembly  22  includes an inner membrane  24 , an outer layer  26 , a plurality of tear-off cords ( 28 ,  30 ), a plurality of eyelets ( 32 ,  34 ) and a fill shaft  36 . As illustrated in FIG. 2 a , the inner membrane  24  is generally parabolically shaped and closely matches the shape of the spacecraft  16  previously illustrated in FIG.  1 . The inner membrane  24  is preferably a polyester film material such as Mylar™ that is chosen for its low weight properties and compatibility with thermal bonding processes. The polyester film material used for the inner membrane  24  is to be thick enough to avoid easily snagging on the spacecraft surfaces, preferably from approximately 0.0005 to 0.010 inches. 
     A plurality of inner tear-off cords  28  are attached to a surface  38  of the inner membrane  24  parallel to the central vertical axis  42  of the inner membrane  24 . The tear-off cords  28  provide a means for attaching the balloon subassembly  22  to the interior surface of the shroud  14  (illustrated in FIG. 1) and are preferably of a para-aramid fiber material such as Kevlar™ which is strong and low-weight. For the purposes of the preferred embodiment, two inner tear-off cords  28  are illustrated, each spaced from the other and thermally bonded to the surface  38  of the inner membrane  24  from a base  44  to a vertex  46 . The tear-off cords  28  extend beyond the vertex  46  and terminate at an end  47 . To provide additional attachment of the balloon subassembly  22  to a shroud section, the inner membrane  24  utilizes a plurality of eyelet attachments  32  extending along a base  44 . Alternatively, the eyelet attachments  32  may be tabs constructed as an extension of the balloon subassembly  22  or loops constructed as extensions of the tear-off cords  28 . The eyelet attachment selection is determined by the requirements of the shroud  14 . 
     The outer layer  26  of the balloon subassembly  22  is generally parabolically shaped and is fabricated of the same polyester film material as described for the inner membrane  24 . The polyester film material used for the outer layer  26  is to be thick enough to retain the pressure of the gaseous material contained in the balloon subassembly  22  and resist puncture against the shroud  14 , preferably from approximately 0.001 to 0.005 inches. The outer layer  26  contains a plurality of outer tear-off cords  30  attached in the manner similar to that described for the inner membrane  24 . Starting at a base  45 , extending to a vertex  48  and parallel to the central vertical axis  41 , the plurality of outer tear-off cords  30  are attached to a surface  40  of the outer layer  26 . The tear-off cords  30  extend beyond the vertex  48  and terminate at an end  49 . As described with the inner membrane  24 , the tear-off cords  30  and eyelets  34  provide a means for attaching the balloon subassembly  22  to the interior surface of the shroud  14 . 
     Illustrated in FIGS. 2 b  and  2   c , using a thermal bonding or similar process, the outer layer  26  is circumferentially attached to the inner membrane  24  forming a closed volume subassembly  22 . Prior to attachment, the inner tear-off cords  28  are aligned coincident and proximal to the outer tear-off cords  30  and the inner and outer tear-off cords ( 28 , 30 ) form bond lines  60  and at the vertex  52  of the balloon subassembly  22 . Next, the cords ( 28 ,  30 ) are extended through a small thermally sealed hole  50  located at the vertex  52  of the balloon subassembly  22 . As illustrated in FIG. 2 c , a pair of inner cords  28  and a pair of outer cords  30  extend through the vertex  52  of the subassembly  22 . Next, as illustrated in FIG. 2 d , a single member  29  of the inner cord pair  28  is attached to a single member  31  of the outer cord pair  30  forming an integral cord  56 . As shown in FIG. 2 e , the resultant number of integral cords  56  per subassembly  22  is equal to one-half the total number of tear-off cords. 
     Next, as illustrated in FIG. 3, the balloon subassemblies  22  are circumferentially seamed together by a thermal process to form a balloon assembly  12  having a hollow shape and approximating the shape of the launch system shroud  14  shown in FIG.  1 . As further illustrated in FIG. 5, a fill tube  62  is integrally attached to each balloon subassembly  22  fill shaft  36  forming a fully integrated balloon assembly  12 . 
     During the integration of the spacecraft  16  and the shroud  14  to the launch vehicle  18 , the balloon assembly  12  is attached to the interior surface of the shroud  14 . As illustrated in FIGS. 1 and 4, each integral tear-off cord  56  (two cords per balloon subassembly  22 ) is attached to a segment of the top interior surface of the shroud  14 . Specifically, the tear-off cords  56  are evenly distributed and attached circumferentially to the top interior surface of the shroud  14 . The eyelets  35  of the balloon assembly  12  are circumferentially secured to the shroud base  58  and the fill tube  62  is attached to an access port  11  on the shroud  14 . Next, as illustrated in FIG. 1, the shroud  14  is placed over the spacecraft  16 , attached to the launch vehicle  18  and the balloon assembly  12  inflated with a gaseous material at the access port  11 . The preferred gaseous material, helium, is chosen for its low transmission ratio (TR) properties. 
     Finally, the vehicle launch system  10  described in the present invention is fully assembled for launch. As previously mentioned, the first three minutes of the launch of any spacecraft from a ground based facility induces an enormous acoustic vibration upon the shroud of the launch vehicle. The acoustic vibration on the shroud is then induced onto the spacecraft. As illustrated in FIG. 6, after the first three minutes of the launch, the spacecraft  16  propels upward into the earth&#39;s atmosphere and the shroud  14  separates, after reaching a predetermined altitude, into multiple sections. The splitting of the shroud  14  pulls the cords  56  causing the balloon assembly  12  to rip along the bond lines  60  (see FIG. 2 c ) to form a cleanly segmented blanket attached to the top and bottom of the shroud  14 . The splitting and falling away of the shroud  14  and balloon assembly  12 , allow the spacecraft  16  to continue in an upward motion without impediment. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.