The Space Engineering Research Center (SERC) at M.I.T., started in July 1988, has completed two and one-half years of research. This Semi-Annual Report presents annotated viewgraph material presented at the January 1991 Steering Committee and Technical Representative Review. The objective of the Space Engineering Research Center is to develop and disseminate a unified technology of controlled structures. There has been continued evolution of the concept of intelligent structures (including in this past year the first successful embedding of a microelectronic component into a structural element)

Crawley, Edward F.

Miller, David W.

English

NASA Technical Reports Server

NA SA-CR-| 92,]1.15
M.I.T. SPACE ENGINEERING RESEARCH CENTER
Semi-Annual Report: January 1991
Professor Edward F. Crawley, Director
Dr. David W. Miller, Research Associate
May 1991 SERC # 4-91-R
(Under the Sponsorship of NASA)
J
(NASA-Ce-192115) MIT SPACE
ENGINEERING RESEARCH CENTER TESTBEO
PROGRAMS Semiannual Report t period
endinq Jan. 1Q91 (MIT} 340 p
N93-21660
Unclas
G3/99 01_3810
https://ntrs.nasa.gov/search.jsp?R=19930012471 2020-03-17T06:30:14+00:00Z

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'Engineering
Xesearch
4¥nter
CONTENTS
Overview, Objectives and Progress
• SERC Testbed Programs
Presentations
• Material and Structural Damping from Nan.strain to Millistrain
• The Virtues of Passive Damping in Controlled Structures
• A Systems Engineering Approach to Disturbance Minimization for
Spacecraft Utilizing Controlled Structures Technology
• Isolation
• Using Input Command Pre-Shaping to Suppress Multiple Mode
Vibration
• Development of Area Averaging Sensors for Active Structural
Control
• The Zeroes of Controlled Structures: Sensor and Actuator
Attributes and Structural Modelling
• Active Broadband Impedance Matching
• Cost Averaging Techniques for Robust Control Synthesis for
Parametrically Uncertain Systems
• Control of a Class of Systems with Parameter Uncertainty
• Preliminary Design of Controlled Structures

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"Engineering
_esearcti
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OVERVIEW
The Space Engineering Research Center (SERC) at M.I.T., started in
July 1988, has completed two and one-half years of research. This Semi-
Annual Report presents annotated viewgraph material presented at the
January 1991 Steering Committee and Technical Representative Review.
The objective of the Space Engineering Research Center is to develop
and disseminate a unified technology of controlled structures. There has
been continued evolution of the concept of intelligent structures (including
in this past year the first successful embedding of a microelectronic
component into a structural element). Nine faculty and thirty-five graduate
students and a like number of undergraduates through the Undergraduate
Research Opportunity Program (UROP) participate in the activities of
SERC, drawn from the Departments of Aeronautics and Astronautics,
Electrical Engineering and Computer Science, and Mechanical
Engineering.

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Spacecraft Disturbances
0.01 1 200 (0 (Hz)
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II.
III.
IV.
Exponential (E): 10 -6 => 10-2 Hz
A. Environmental disturbances (GGT, Aero, Rad'n, Mag'nt)
B. Gross thermal-mechanical deformations
Low
A.
Frequency Periodic CL): -10 "2 :> 1 Hz
Flexi-body interaction torques (damping), and momentum exchange with flexible
appendages and movable elements; vehicle fundamental modes
B. Internal thermal-raechanical fluctuations: active cycling of elecmc heaters; cyclic
operation of dissipating devices
C. FIiud slosh: propellant, cryogenics
D. Low frequency electromechanical
B.
C.
Frequency Periodic (M): -I => 200 Hz
Elecn'omechardcal devices: RWA/CMG's, data recording devices, servomechanisms,
pumps, displacement actuators, active mounts,etc.
'Stiffer' flexi-body interactions
Higher harmonics of fluid slosh
High
A.
B.
Frequency Periodic (H): -200 => + Hz
Higher harmonics of electromechanical devices
Electrical noise: AC current
V. Random (R):
A. Fluid turbulence: broadband
B. Friction
C. Sensor/electrical noise (photon, thermal, shot): broadband
D. Micromete, oroid impact: very low fmq
E. Non-periodic gimballing (thrusters, sensors, antennae): low freq
F. Thruster fwing - transients: low-high freq
Space _.r_n_,_ng _a:rc/i Onur
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CST Tools
Passive Structural Techniques:
Structural Design
Thermal Control Techniques
"'Zero" CTE Structures
Structural Tailoring (Jacques)
Passive Damping:
Material Damping
Structural Damping: bonded/mechanical interfaces
Space Viscoelastics
Friction Dampers
Vibration Absorbers: resonant / viscous dampers
Shunted Piezoelectrics (Hagood)
Vibration Isolation:
Passive Isolation: soft/tuned mounts
Active Isolation (Schribner, Stampleman,...)
Active Structural Control: (Control Weenies,...)
Active Damping
Shape Control
Optical Compensation Techniques:
Active Optical Elements, Delay Lines,...
Image Reconstruction Techniques,...
Attitude Control System
Space Engineering P_earch Center .
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Space-Based Interferometer:
OPTICS
Eoui_omem Platform:
CMG Module
Magnetic Torquers
Battery Pack
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High Gain (TDRSS)
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Illustrates Need for Total System Approach:
Distributed Disturbances and Sensitive Elements (Optics)
ACS; Science / Guidance Interferometer
Internal / External Laser Metrology
CST Tools; Optical Compens.; Image Reconstruction;...
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Numerical Model
Space Enaineering P_earch Center
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Disturbances
ORBITAL - "Static"
• Gravity Gradient 0.5 _tg / m offset from the
platform c.g. in the direction of
the orbital radius in LEO
2
5 meter bays
Space Station Low Frequency Acceleration gradient
• Aerodynamic The major disturbance torque in
LEO
• 1 gg is approximately a 3 mm sinusoid at 0.01 Hz
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Isolation of a Space Station
Laboratory Facility
AccelerationEnvironment and Specification:
re__f: Jones, Owens, and Owen, "A Microgravity Isolation Mount,"
Acta AstTonautica, Vol. 15, No. 6/7 1987
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a = desired
b = anticipated
c = required
isolation
Mount travel of less than I cm. must be
accommodated
• Prevent 6 axis payload drift (bias force - 1 raN)
Accommodate umbilical cord (uncertain dynamics)
or non-contact substitutes which allow
1) Data Transfer,
2) Payload Cooling, and
3) Power Flow.
• Passively stable, graceful failure
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Not Passive Isolation?
basebody
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km Mount stiffness
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Control/Isolation Goal is to lower the resonant
frequency, fr, below 0.01 Hz
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Open loop response
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Isolation
specification
d Desired closed loop
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@ Km = 40 N/m to bury the uncertain umbilical cord
dynamics
• Axes decoupled by using modal analysis
@ At least a factor of 10 active enhancement of
isolation is necessary between 0.01 Hz and 10 Hz
@ Compensator (each axis) from accelerometer to
control force is lag/lead,lead/lag
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Mount is essentially passive outside the active range
of 0.01 Hz < f < 1 Hz
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The PVDF Actuator
(SIZED TO OVERCOME A 40 N/M MOUNT STIFFNESS WHICH
INCLUDES BOTH THE ACTUATOR AND UMBILICAL CORD)
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Layered PVDF piezoelectric film used in a
"bimorph" format
Arcs can be used in various configurations as semi-
active mounts
Each Arc: • internal modes > 40 Hz
• can overpower itself for I cm.
travel
• workable example:
width = 0.05 m
radius = 0.04 m
layer thickness = 28 _Lm
number of layers = 6
force @ 1 cm. travel = 0.12 N
piezoelectric induced
force = 0.13 N
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Accomplished: (1990)
3-axis experiment operating:
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Summary
• Microgravity isolation is easily achievable
Active isolation only required by stiff umbilical cord
• This mount is passive with active enhancement
Future Work
• Six axes ground demonstration too difficult
Perform 3 sequential 3-axis demonstrations with 6-
axis hardware
• Fly with a microgravity customer


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MIT Space Engineering Research Center testbed programs

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