Ordnance – Shields – Shape or composition
Reexamination Certificate
1998-12-02
2001-10-09
Johnson, Stephen M. (Department: 3641)
Ordnance
Shields
Shape or composition
C089S036070
Reexamination Certificate
active
06298765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the protection of spacecraft from hypervelocity impactors and more particularly to a stand-alone, self-contained impact shield assembly for protecting a spacecraft surface from such hypervelocity impactors.
2. Description of the Related Art
Designing spacecraft for the future has introduced many new challenges. One such challenge is to provide affordable, maximum protection against the ever increasing threat of man-made orbital debris. As spacecraft soar into near-earth orbits they share orbital space with thousands of large and perhaps tens of millions of medium-sized debris objects left from 3,800 previous space missions since 1957. It has been estimated that the total amount of debris orbiting below 1,240 miles is between 8.5 and 10 millions pounds and is increasing. The average accidental impact velocity between spacecraft and orbital debris in this region is 10 kilometers per second (22,300 miles per hour) and can reach velocities as high as 15 kilometers per second (34,000 miles per hour). At these velocities, a piece of debris no larger than a garden pea carries the destructive punch to potentially cripple an entire unprotected spacecraft.
Currently, spacecraft (particularly manned spacecraft) use bulky, heavy metallic “bumpers” to protect critical areas. These bumpers, which usually consist of thin aluminum sheets placed 4 to 8 inches off the surface they are protecting, are designed to be perforated when impacted by a meteoroid or debris particle while shocking the particle and breaking it into fragments. These fragments disperse in an expanding debris cloud which spreads the impact energy over a much larger area, making it far less damaging to the surface behind it. If the impacting velocity is high enough, melting or vaporization will occur, which aids in reducing impact lethality.
The shortcomings associated with the standard metallic bumper concept are numerous. First and most importantly, metallic bumpers are very heavy. Since bumpers are the outer-most spacecraft surface, their large surface area translates to excessive weight. In addition, in order to survive the rigors of launch, bulky structure is necessary to support these bumpers. The industry rule-of-thumb is that metallic bumpers and support structure are expected to contribute approximately 5-10% to the total vehicle weight.
Secondly, high performance metallic bumper concepts often violate payload volumetric constraints. The volume consumed by such designs is significant when bumper shields protrude out 4 to 8 inches from the vehicle surface they are protecting. This space is preferable for functional equipment.
Thirdly, metallic bumper shields often experience thermal expansion and heat transfer related problems on-orbit because of the extreme temperatures. Design complexity is often necessary to alleviate these problems. Finally, metallic bumpers offer no real means of on-orbit augmentation without excessive vehicle design and/or configuration impacts.
U.S. Pat. No. 5,067,388, issued to Crews et al. discloses a hypervelocity impact shield that utilizes layers of impactor disrupting material which are spaced apart to progressively shock the incoming meteoroid or orbital debris particle to a vapor state which increases the penetration resistance dramatically. This concept is believed to provide the maximum passive protection of any heretofore existing shield design. The major shortcoming of the '388 shield is that there is no practical or efficient means disclosed in that patent for spaceably supporting the impactor disrupting material.
Present applicant is aware that current applications of the concepts described in the '388 patent have involved conventional rigid metallic support structures which are heavy, bulky and cumbersome. Such support structures prohibit their usefulness for spacecraft applications.
U.S. Pat. No. 5,610,363, also issued to Crews et al. discloses a hypervelocity impact (HVI) whipple shield and a method for shielding a wall from penetration by high velocity particular impacts where the whipple shield is comprised of spaced apart inner and outer sheets or walls with an intermediate cloth barrier arrangement comprised of ceramic cloth and high strength cloth which are interrelated by ballistic formulae.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to provide an efficient means of protecting a vulnerable spacecraft surface from hypervelocity impactors, such as meteoroids and orbital space debris.
In a broad aspect, the present invention comprises a hypervelocity impact shield assembly for protecting a spacecraft surface from hypervelocity impactors. The shield assembly includes at least one sacrificial impactor disrupting/shocking layer of hypervelocity impactor disrupting/shocking material. A primary spacing element, including space-rated open cell foam material, is positioned between the at least one sacrificial impactor disrupting/shocking layer and a spacecraft surface. A cover member is arranged and disposed relative to the sacrificial impactor disrupting/shocking layer and the primary spacing element to maintain the integrity of the hypervelocity impact shield assembly. In the event of exposure to a hypervelocity impactor, the sacrificial impactor disrupting/shocking layer is perforated while shocking the impactor breaking it into fragments, and/or melting it, and/or vaporizing it, thus providing a dispersion in the form of an expanding debris cloud/plume which spreads the impact energy of the impactor over a volume formed by the primary spacing element between the sacrificial impactor disrupting/shocking layer and the spacecraft surface. This significantly reduces impact lethality at the spacecraft surface. The space-rated open cell foam material provides an extremely lightweight, low-cost, efficient means of spacing and supporting the at least one sacrificial impactor disrupting/shocking layer before, during, and after launch.
In a preferred embodiment, the invention is in the form of a multi-shock assembly including a plurality of sacrificial impactor disrupting/shocking layers. In such instance, the hypervelocity impact shield assembly includes a plurality of secondary spacing elements. Each secondary spacing element is positioned adjacent an associated sacrificial impactor disrupting/shocking layer to form a multi-shock subassembly. Thus, a plurality of multi-shock subassemblies are provided which include alternating layers of sacrificial impactor disrupting/shocking layers and secondary spacing elements. The resulting multi-shock assembly includes a plurality sandwiched multi-shock subassemblies and the cover member arranged and disposed relative to the multi-shock subassemblies and a spacecraft surface to maintain the integrity of the multi-shock assembly.
The multi-shock assembly provides the high performance of the invention disclosed in the Crews et al. U.S. Pat. No. 5,067,388, without the necessity of burdensome support structures.
These and other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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Christiansen E L, Kerr J H, De La Fuente H M, Schneider W C: Flexible and deployable meteoroid/debris shielding for spacecraft: Proceedings of the 1998 Symposium “Hypervelocity Impact”, Nov. 17-19, 1998, pp. 125-136, XP000904895; Huntsville, AL, USA.
Shortcliffe G, Christiansen E: “NASA
Ginsberg Lawrence N.
Johnson Stephen M.
McDonnell Douglas Corporation
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