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Very High Damping Can Reduce Launch Loads and Operational Jitter 1
Very High Damping Can
Reduce Launch Loads
and Operational Jitter
June 26-28, 2007
L Porter Davis
Honeywell International 2
There is a broad range of structural
control product
WB-57
IPS
Precision Sensor Isolator
Othel
lo D-
Strut
MOCA
Isolator
MAVIS
Expedition
Isolator
MCS/LOS Testbed Isolator
MVIS II
MVIS 3
Structure control categories with focus on Damping
Problem
Frequency Description
Solution Product Application
A few appendage
modes
Many structural
resonances
High frequency
base motion
Payload disturbance
and pointing, low
frequency base motion.
Launch induced
vibrations on entire
spacecraft
Tuned Mass Damper
D-Strut
TM
Structural Damper
D-Strut
TM
Passive Viscous Isolator
Hybrid
D-Strut
TM
(VISS)
Launch
Vehicle Isolation System
(LVIS) 4
Hubble provided the first Flight for the D-Strut
Product Specifications
Attenuation at 100 Hz = 0.1
Break Frequency = 20 Hz
Amplification = 3 to 6
Alignment Stability
Random Vibration = 6 grms
Sine Wave = 1.5 g
Payload Weight = 195 Lb
Isolation System Weight = 4.0 Lb.
Element Weight = 1.3 Lb.
No. of Elements = 6 per RWA
No. of Isolation Axes = 1
Envelope = 24 OD x 6 in.
Temperature Range = -10 to +110F
Life = 7 to 17 years
Features
HST RWA
HST RWA
Isolator
Isolator
Vibration Force
Without Isolation
Vibration Force
With Isolation 5
D-Struts are linear over a large dynamic range
HST RWA D-Strut Performance
M
K
A
K
B
C
A
Input
Output 6
Its an isolator but why not a damper
Damper 7
D-Struts shown in truss 8
The D-Strut as a damper
Fluid
Inner tube
Outer tube 9
Advanced D-Strut designs
Multi convolute Flexure
Arched Flexure 10
Many Spacecraft use struts
The DSP satellite is one
example of spacecraft that
use trusses and struts
. 11
The D-Strut provides 3 Parameter Damping
M
K
C
M
K
A
K
B
C
A
Conventional
Two-parameter
Isolator
Three-parameter
Isolator
Two-Parameter Systems = 20 dB/decade roll-off
Three-parameter Systems = 40 dB/decade roll-off 12
Three Parameter Characteristics 13
Converting D-Strut parameters to the
basic three parameter form






+
+






+
=
4
3
4
2
2
3
2
1
1
1
1
k
k
k
k
k
k
k
k
B
















+
+
=
2
3
1
3
1
1
k
k
k
k
k
A
2
2
3
1
1






+
=
k
k
c
c
A 14
Three parameter transmissibility 15
Several designs have been tested
Representative Flexible Bus Structure
Attitude Control
- RWA/CMGs
- Momentum Systems
- GPS/IMU
Passive Structural Control
- D-Struts
TM
- Tuned Mass Dampers (TMD)
Input Isolation
- Isolated RWA/CMGs
- Isolated Momentum Array
- SAD IV Reduction
Active Structural Control
- Hybrid D-Struts
TM
- Proof Mass Actuators
- Fiber Optic Sensors
Structural ID/Control
- Autonomous Identification
- Command Input Shaping
- Modern Control Theory
Precision Payload Isolation
and Pointing
- VISS Hexapod
- Two-Axis Gimbal
- Inertially Stabilized Bench
10
-1
10
0
10
1
10
2
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
Hz
g/
l
b
Testbed: predicted transfer functions 16
Effect of damping Space Station structure
Settling time reduced by an
order of magnitude
Control Bandwidth could
be significantly increased 17
A JPL test shows D-Strut effectiveness 18
Space Active Vibration Isolator (SAVI)
Focus: Active Magnetic Isolation
and Pointing
4 deg pointing, 27,000 N-m retarget
torque, 4.8 meter CG offset
80 dB Isolation from 1 - 2000 Hertz
using Honeywells Magnetic
Suspension Technology
Testbed was integrated in Kirtland
AFB
Full-scale 5.6m Cassegrain beam
expander with Gravity Offload
3000 kg (1/3 structural, 2/3 mirror),
1st mode 8-10 Hertz
Later became the SPICE Testbed
Damping was needed in
primary Backing structure 19
D-Strut
TM
Structural Damper SPICE
3150 lb
2.48 in.
40.61 in.
80,000 lb/in.
160,000 lb/in.
>40%
2.45 lb
Load Capacity
Outside Diameter
Length
Static Stiffness
Dynamic Stiffness
Maximum Loss Factor
Weight
Characteristics 20
A Proposed launch adaptor needed a
highly damped Isolation System
10
-1
10
0
10
1
10
2
10
3
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
Direct Transmissibility
Frequency (Hz)
Ga
i
n


X-to-X
Y-to-Y
Z-to-Z x-to- x y-to- y z-to- z
D-Strut damping
required
Space Craft
Adapter Fitting
Payload Adapter
Fitting (PAF) 21
Flexure, Endcap
and Retainer
Composite
Tube
Honeywell D-strut
Adapter
Worm Gear
Preloader Interface
Adjustable
Stop Gap
Adjustable
Stop Housing
Payload suspension system requires high
damping levels 22
Summary
The use of D-Struts as compliant isolation systems has
been readily accepted for satellites and launch vehicles.
This acceptance is primarily due to the increased vibration
attenuation possible with the three-parameter D-Strut.
The application of D-Struts in rigid structures has not been
widely utilized.
This presents an opportunity for further
improvement in the structural control of spacecraft and
launch vehicles. 23
Rigid D-Strut Papers
"Viscous Damped Space Structure for Reduced Jitter", 1987
58th Shock and Vibration Symposium
"Very High Damping in Large Space Structures", 1987 ASME
"New Structure Design Criteria Offer Improved Pointing and
Lower Weight", 1988 59th Shock and Vibration Symposium
"Testing and Application of a Viscous Passive Damper for the
Use in Precision Truss Structures", 1991 SSD&M Conference
"D STRUT", An Advanced Arched Flexure, Damping '91
"Design, analysis and testing of High Frequency Passively
Damped Struts", Fifth NASA/DOD Control - Structures
Interaction Technology Conference, March 1992, co-authors
from AMSC and the Phillips Lab Airforce
"Testing and Application of a Viscous Passive Damper For use
in Precision Truss Structures", L.P. Davis, Dr. E. Anderson MIT,
sponsored by Wright Paterson Airforce, in San Diego, CA