Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2000-03-21
2001-03-20
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C188S378000, C244S118100, C267S151000
Reexamination Certificate
active
06202961
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to passive shock load isolation apparatus suitable for use on spacecraft launch systems.
Spacecraft launch systems present severe requirements for shock load isolation apparatus. Shock loads are typically large magnitude disturbances having vibration energy at 100 Hz and above and can be of a transient or continuing nature, and can have both spacecraft axial and lateral directional components. During launch and during spacecraft separation from the launch vehicle, substantial shock load vibration energy is transmitted from the launch vehicle to the more delicate spacecraft. This loads environment drives up the size and strength requirements of the spacecraft and spacecraft-to-launch vehicle interface hardware. In the development of shock load isolation apparatus, as with any space-flight hardware, the mass and space requirements of the apparatus must be aggressively minimized so to reduce the cascading design impact to supporting hardware and thereby reduce the associated additional development and launch costs. Additionally, the overall system dynamics of the spacecraft and launch vehicle system must be predictable and carefully controlled in design so to allow controlled and stable flight. With the desire to launch a wide array of payloads comes the need for shock load isolation apparatus that can be easily scaled up or down to accept the broadly ranging size and mass of the spacecraft structures. And perhaps most importantly, the high costs and lengthy development times associated with satellites and other space bound hardware require that a premium be placed on obtaining durable and reliable spacecraft mounting hardware. Because the shock isolation mount, to be effective, must be the only connection of the spacecraft to the launch vehicle, it must meet these demands of high durability and reliability in concert with its shock isolation characteristics.
One described spacecraft axial vibration isolator is disclosed in U.S. Pat. No. 5,961,078. This patent claims that a payload attachment interface ring can be utilized to add axial compliance to the payload and launch vehicle interface by staggering the attachment points of the payload relative to the attachment points of the interface ring to the launch vehicle. This patent also suggests that damping can be added to the inherent damping of the payload attachment interface ring by making the ring a laminate which includes a ‘yieldable material to provide inherent hysteresis qualities’. The reality and deficiency of this concept for shock load isolation is that little additional axial compliance and deflection can be added without encountering stress failures in the payload attachment interface ring. The compliance gained is a simple addition of the beam bending and beam torsion compliances of the payload interface ring induced by staggering the payload attachment points relative to the base structure support pads. More importantly, the damping available within this concept from the bending and torsion of the interface ring material is commonly quite small, and provides relatively little damping to shock loads. Also, since the deflections of the interface ring are limited by the failure stress limits of the interface ring's load carrying material, the additional damping possible by making the ring a laminate including a yieldable material is severely limited. The more substantial axial compliance and damping characteristics necessary for effective shock load isolation may have been part of the ‘specially designed flexure feature’ referred to in this patent's description, but it is neither described nor claimed.
A lateral force vibration isolator is claimed in U.S. Pat. No. 6,012,680. This patent discloses a concept of a payload attachment structure incorporating a circular array of beam flexures arranged to allow lateral compliance between the payload and supporting base. This concept provides no significant axial compliance nor damping necessary for isolation of the payload from axial shock loads.
U.S. Pat. No. 5,878,980 discloses a device where, to achieve sufficient damping, an elastomer is utilized in the primary load path within the mount of the spacecraft to the launch vehicle. This approach for obtaining damping has been commonly employed in the vibration isolation field, but it results in a mount with the distinct disadvantage of having a significantly lower strength and reduced fatigue life relative to the invention disclosed, which provides high damping but with a complete high strength material load path. The insertion of the elastomer into the primary load path in U.S. Pat. No. 5,878,980 also results in a mount with nonlinear load deflection behavior which complicates the design process and reduces the dynamic performance predictability of the launch system.
BRIEF SUMMARY OF THE INVENTION
The invention described within is a passive, multi-axis, highly damped, shock load isolation mount which can serve as a complete one-piece mount, particularly of a spacecraft to its launch vehicle or launch vehicle adaptor structure, or can serve in multiplicity as necessary to provide a complete shock load isolation mounting system. It provides substantial reduction in shock load transmission from support base to payload for both axial loads and lateral loads, as can be seen in response spectra charts of test data in
FIGS. 9 and 10
, and does so in a package that's simple, light-weight and compact.
The assembled device is of one-piece, typically cylindrical ring construction and is essentially a cylindrically shaped flexure body encased on its outer and/or inner cylindrical surfaces by a viscoelastic material (VEM) layer and a stiff constraining layer. The payload attaches to one end of the cylindrical flexure body and the launch vehicle or support base attaches to the other end of the cylindrical flexure body.
The cylindrical flexure body is of novel design and is comprised of a multitude of layered rings of beam flexures wherein ideally a staggered pattern of closely nested beam flexures having opposed beam bending deflection is effected. These beam flexures can be created by simple material removal from a cylindrical tube or by the assembly of multiple rings with appropriately spaced standoff posts. The standoff posts of one ring of beam flexures acts as the load application points to the next ring of beam flexures, and the resulting nesting of beam flexures allows significant compliance to be developed within the overall flexure body without overstraining any one flexure. The low mounting compliance necessary to effect the desired vibration isolation frequency for the spacecraft is thereby achieved. Additionally, the alternating position of the standoff posts between rings of beam flexures within the mount is designed to create a contorted and lengthy load path between vehicle and spacecraft which significantly impedes the transfer of high frequency shock energy.
FIG. 9
shows the substantial reduction of transferred axial shock load between 500 Hz to 10,000 Hz by use of the invention.
FIG. 11
shows the time history of the axial transient acceleration response of a payload relative to its base by use of the invention.
FIGS. 10 and 12
show corresponding plots of the invention for the concomitant reduction of lateral shock loads.
An additional novel aspect of the invention is the orientation of the constrained VEM layer relative to the beam flexures. The VEM and constraining layers, rather than laying on the top of the flexure and being forced to bend with the flexure, are affixed to and across the sides of the beam bending flexures in the manner of a shear wall and thereby oppose the relative translational motion between beam flexures. (See
FIG. 3
for a cross section of the isolation mount, which shows this physical relationship of the VEM and constraining layers relative to the beam flexures.) The relative translational bending movement of the opposed flexures, even though minor, induces significant shear into the constrained VEM layer. The mult
Johnson Conor D.
Pendleton Scott C.
Wilke Paul S.
Barefoot Galen L.
Brewster Rick G.
CSA Engineering
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