The status of the Dynamic Scale Model Technology (DSMT) research program is presented. DSMT is developing scale model technology for large space structures as part of the Control Structure Interaction (CSI) program at NASA Langley Research Center (LaRC). Under DSMT a hybrid-scale structural dynamics model of Space Station Freedom was developed. Space Station Freedom was selected as the focus structure for DSMT since the station represents the first opportunity to obtain flight data on a complex, three-dimensional space structure. Included is an overview of DSMT including the development of the space station scale model and the resulting hardware. Scaling technology was developed for this model to achieve a ground test article which existing test facilities can accommodate while employing realistically scaled hardware. The model was designed and fabricated by the Lockheed Missile and Space Co., and is assembled at LaRc for dynamic testing. Also, results from ground tests and analyses of the various model components are presented along with plans for future subassembly and matted model tests. Finally, utilization of the scale model for enhancing analysis verification of the full-scale space station is also considered

Edighoffer, Harold H.

Javeed, Mehzad

Mcgowan, Paul E.

English

NASA Technical Reports Server

NASA Technical MemorandUm-r02764
STATUS OF DSMT RESEARCH PROGRAM
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Paul E. McGowan, Mehzad Javeed, and llarold It. Edighoffer
January 1991
NA. A
National Aeronautics and
Space Administration
Langley Research Center
Hlu'npton,Virginia 22865
(NASA-TM-IO_?&4) STATUS
PROGRAM (NASA) _I p
OF DSMT RESEARCH
CSCL 20K
N91-20505
Unclos
O0012q_
https://ntrs.nasa.gov/search.jsp?R=19910011192 2020-03-19T18:32:11+00:00Z

STATUS OF THE DSMT RESEARCH PROGRAM
Paul E. McGowan
NASA Langley Research Center
Hampton, VA
Mehzad Javeed
Lockheed Engineering & Sciences Co.
Hampton, VA
Harold H. Edighoffer
Analytical Services & Materials, Inc.
Newport News, VA
ABSTRACT
The status of the Dynamic Scale Model Technology (DSMT) research
program is presented. DSMT is developing scale model technology for
large space structures as part of the Controls Structures Interaction (CSI)
program at the NASA Langley Research Center (LaRC). Under DSMT a
hybrid-scale structural dynamics model of Space Station Freedom has been
developed. Space station was selected as the focus structure for DSMT
since the station represents the first opportunity to obtain flight data on a
complex, three-dimensional space structure. Included in the paper is an
overview of DSMT including the development of the space station scale
model and the resulting hardware. Scaling technology was developed for
this model to achieve a ground test article which existing test facilities can
accommodate while employing realistically scaled hardware. The model
was designed and fabricated by the Lockheed Missiles and Space Co.,
Sunnyvale, CA, and is assembled at LaRC for dynamic testing. Also, results
from ground tests and analyses of the various model components are
presented along with plans for future subassembly and mated model tests.
Finally, utilization of the scale model for enhancing analysis verification of
the full-scale space station is also considered.
SPACESTATION FREEDOM
Verification of analytical models for spacecraft has historically been
accomplished through ground tests of space hardware prior to flight.
Due to the large size and flexibility of current space structure
designs, ground tests of full-scale hardware may be limited to
components and subassemblies. An example of such a structure is
the proposed design for Space Station Freedom, which consists of an
erectable truss structure interconnecting a number of flexible
components, payloads and modules. When fully assembled the
station has planform dimensions of approximately 200 ft. by 550 ft.,
weighs approximately 600,000 lbs, and its lowest natural vibration
frequency is much lower than 1 Hz. No practical method exists for
verifying through ground tests an integrated configuration of this
structure. Thus, analysis models for structural dynamics predictions
will be verified primarily through synthesis of component analysis
models.
Ground tests of dynamically scaled models offer a potential to verify
analysis methods for prediction of dynamic characteristics of large,
flexible space structures. The use of scale models for structures such
as space station is relatively new, but scale models do have a firm
historical basis in the aircraft and space launch vehicle fields.
Although the scale model may not replicate exactly the full-scale
hardware, it can be used to examine sensitivity of the complete
system response to modeling accuracy at the component level. By
using the same analysis methods for predicting the sc-ale model
dynamics as those proposed for the full-scale system, the accuracy
and viability of those methods can be evaluated.
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O_GINAL PAGE IS
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DYNAMIC SCALE MODEL TECHNOLOGY
As part of the Control Structures Interaction (CSI) program at the
NASA Langley Research Center (LaRC), the Dynamic Scale Model
Technology (DSMT) project is developing scale model technology for
large space structures. The objective of DSMT is to use scale models
for verification of analytical methods for complex space structures
which are too large to be ground tested. Space station was selected
as the focus structure for DSMT since the station represents the first
opportunity to obtain flight data on a complex, three-dimensional
space structure. Under DSMT two laboratory models have been
developed, namely, a generic simulated model and a hybrid-scale
model. The scale model hardware consists of an erectable truss
structure and includes many flexible components, modules and
payloads which can be assembled to represent various stages of
Space Station Freedom. Since the model is a good representation of
space station it also provides a test-bed for examining some key
technical issues such as understanding interactions between flexible
components and the global truss structural modes.
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DSMT RESEARCH AREAS
Depicted in the figure., are the main research areas which are being
studied using the hybrid-scale space station model. Since DSMT is a
technology program these research areas are selected to address
broad technical issues pertaining to other spacecraft structures as
well. The eight major areas are interrelated and essentially involve
validation of scaling laws, verification and improvement of analysis
models through ground vibration tests, development of advanced
suspension systems, validation of on-orbit experiment designs,
substructure synthesis approaches, and development of damage
location approaches. In this paper only the scaling, ground test and
analysis approaches are addressed.
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DSMT TEST/ANALYSIS VERIFICATION APPROACH
The approach adopted for verifying analytical models of the hybrid
scale model consists _,of performing test/analysis updates at the
component, substructure, and finally assembly sequence levels. As
component models are refined that information is used to develop
improved substructure analysis models which in turn lead to more
accurate representations of the build assembly configurations. This
approach parallels that of the full-scale space station program with
the exception that DSMT can examine mated assembly configurations
whereas space station cannot.
For the hybrid-scale HMB-2 model, the structure has been
subdivided into twenty two components. These components are
generally in one of four categories, namely, 1) truss structure, 2)
appendages, 3) pallets, and 4) articulating joints. Each component
will be individually tested and the corresponding analytical model
will be updated to reflect the results of test data analysis. At the
intermediate level substructures consisting of two or more
components will be tested and analyzed to insure that the fidelity of
the analytical model is preserved at all levels of complexity. Finally,
the MB-2, MB-5, and MB-15 configurations will be studied to
evaluate the primary object of this research program.
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1/10-SIZE GENERIC SPACE STATION MODEL (GMB-2)
The Generic MB-2 configuration space station model (GMB-2) is a
1/10-size simulated r0odel utilizing commercially available truss
hardware known as MEROFORM. In the figure the GMB-2 model is
shown suspended in the configuration used for dynamic testing. The
model was designed to simulate the dynamics of the more
complicated hybrid-scale model. Simulated appendages were
fabricated to have characteristics resembling the hybrid model. The
model was used to study and evaluate analytical modeling and
analysis techniques as well as experimental testing methods prior to
examining the hybrid model.
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11
SUSPENDED GENERIC MODEL TEST/ANALYSIS COMPARISONS
The generic GMB-2 model suspended by six cables was analyzed
using an MSC/NASTRAN finite element model and was compared
with the test results. An initial finite element model was developed
based on component test/analysis correlations. This initial model
still produced some inaccurate predictions of higher modes. An
updated model which was in good agreement with test results was
developed by performing additional model refinement especially at
the main structural interfaces. Mode No. 4, the rigid body roll mode
was improved because of the improved mass distribution of the
components giving the correct roll mass moment of inertia. Several
of the solar array and radiator modes dominated the equivalent
system modes. Thus, the solar array and the radiator truss mounting
plates were revised at the component level to correct the plate
bending stiffness and match the static and dynamic response at the
component level. These appendage modes matched the analysis at
the component level and then correlated at the system level without
additional adjustments.
12
013
DSMT HYBRID-SCALE MODEL
Shown in the figure is a hybrid-scale structural model of an early
Space Station Freedom assembly configuration (MB-2). Hybrid-
scaling refers to the _,1/5"1/10 scale factor applied to the model
design. Hybrid scaling technology was developed for this model to
achieve a ground test article which existing test facilities can
accommodate while employing realistically scaled hardware. All
truss planform dimensions have been scaled to 1/10-size of the full-
scale station design. The truss nodal joints, mass and frequencies are
l/5-scale. This design provides a model which can be tested in
existing facilities, yet has the low frequency dynamics characteristic
of the station structure. The model was developed by the Lockheed
Missiles and Space Company, Sunnyvale, CA. The MB-2 configuration
consists of ten truss bays which are connected by an articulating
rotary joint and on which a number of solar arrays, radiators and
pallets are mounted. Ground tests of this model will be performed at
LaRC to develop techniques for predicting the on-orbit dynamic
response of such structures.
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ORIGINAL PAGE IS
OF POOR _,-_/_;Tt'
DSMT HYBRID-SCALE MODEL DYNAMICS
Hybrid scaling provides a dynamically scaled space station model
such that a realistic test article can be obtained for developing test
and suspension techniques required for verifying analytical models.
Hybrid scaling employs classical distorted scaling techniques, which
have historically been used extensively for wind tunnel models.
When used for large space structures it permits the use of different
scale factors for the truss structure components, appendages and
payloads while sacrificing local dynamic behavior, but retaining
overall global dynamics behavior. The hybrid-scale model truss
structure bay size and truss joint components were selected to be
1/10 and 1/5 scale, respectively. This results in a model which is
small enough (50' x 30' planform) to be assembled and tested in an
existing LaRC facility. Furthermore, the 1/5-scale joints are
essentially the minimum size at which erectable joints can be
fabricated without incurring large manufacturing costs or
compromising joint performance. Properly distorting the truss
component stiffnesses and masses yields a model which possesses
the same global dynamic properties as would a fully l/5-scale
replica model. Some of the scale factors which apply to the hybrid
model are listed in the figure.
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DSMT HYBRID-SCALE MODEL FEATURES
The DSMT hybrid-scale model utilizes erectable joints and modular
components such that any number of space station configurations can
be assembled. This allows the model to be representative of each of
the approximately 20 assembly flights required _ to _ reach the
assembly complete station. Depicted in the figure are the three focus
configurations selected for study. The MB-2, MB-5, MB-15
designations refer to space station mission build configuration
numbers. As seen in the table these three structures span a wide
range of structural parameters. Also, by varying mass properties of
the payload components, the hybrid-scale model structure can be
adjusted to reflect changes in the station design.
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DSMT GANTRY TEST FIXTURE
The gantry fixture is the support structure for the DSMT hardware.
The fixture is capables, of supporting various configurations of the
DSMT space station model. There are currently two working
platforms at 20 ft. and 40 ft., and the gantry can be expanded to 60
ft. These platforms allow for numerous support locations as well as
various support mechanisms. The structural characteristics of the
gantry are known and uncoupled from the current suspended
models. Provisions were made to have the capability to remove
some structural members from the gantry for positioning of large
models.
20
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ORIGINAL PAGE IS
OF POOR QUALITY
VIBRATION FREQUENCIES FOR HYBRID-SCALE
HMB-2 MODEL SUSPENDED BY FOUR CABLES
The !iybrid-scale HMB-2 model suspended by four cables was
evaluated using an MSC/NASTRAN finite element model. Depicted in
the figure is the modal density for this structure in the suspended
configuration. There are 37 modes in the frequency range of interest
from (0-25 Hz), 11 Of these modes are considered global structural
mode':. Analysis of this structure required that the cable forces
needed to keep the model level due to gravity loading be determined
using a static analysis. The second step was to perform a non-linear
analysis imposing preload cable strains and gravity forces to arrive
at the, deformed level position with the correct cable forces. The
final step was to perform the normal modes analysis using a
combined stiffness matrix consisting of the elastic stiffness plus the
differential stiffness due to the internal forces from the second step.
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DSMT COMPONENT TEST/ANALYSIS RESULTS
A number of components from the HMB-2 scale model have been
examined to d_te. Listed in the figure are the test/analysis
correlations for six components. The initial analysis models were
based on preliminary design information and were developed prior
to fabrication of the hardware. These models were updated based on
the results obtained from the analysis of the test data associated
with each component. In performing the analysis updates the
geometry, mass distribution, and stiffness characteristics of
components are examined and corrected as part of the verification
process. In addition, design sensitivity analysis methods are used to
examine the influence of various physical and material properties on
the component structural characteristics. Information from the
resulting component analysis models are now being included in a
new analysis model of the assembled HMB-2 structure.
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POTENTIAL VERIFICATION MATRIX FOR ON-ORBIT
STRUCTURAL DYNAMICS PREDICTION
For a structure as complex as the space station numerous programs
are required to develop a verification _ matrix which will allow the
accurate prediction of structural dynamics of the mated structure in
zero-g. As shown in the table, DSMT is one important element in
such a matrix, but it alone is not sufficient for complete analysis
verification. DSMT does provide verification of analysis at both the
component and mated levels, but in a 1-g environment. The MODE
experiment provides a zero-g verification of similar hardware to
DSMT, but only at the component level. In addition, there will be
component level full-scale ground tests of space station hardware.
Finally, the proposed MIE project will provide on-orbit data from
components, which are instrumented on the station, and on the
mated station for final analysis verification.
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CONCLUDING REMARKS
DSMT is a technology program which has Space Station Freedom as a
focus structure. The hybrid-scale model hardware is the nucleus of a
broad based research effort which includes the development of
ground tests and analysis methods for a large cla§s of structure. Due
to the resemblance of the scale model to space station, DSMT does
provide a ground test-bed for examining key technic_al i_s_sues. Also,
the approach for analysis verification does parallel that proposed for
space station, with the added benefit of providing mated structure
test/analysis correlation. Finally, the use of scale models should be
considered an integral part of an overall verification plan for a
Complex spac_ structure.
28
29
iI. Repod No
NASA TM-I02764
Report DoEumentation Page
4. Title and Subtitle
2. Government Accession No.
Status of DSMT Research Program
7. Authorls)
Paul E. McGowan, Mehzad Javeed, and
Harold H. Edighoffer
9. Performing Organization Name and Address
NASA Langley Research Center
Hampton, VA 23665-5225
12. Sponsoring Agency Name and Address
National Aeronautics and Space Administration
Washington, DC 20546-0001
1,5. Supplementary Notes
3. Recipier,t's Catalog No.
5. Report Date
January 1991
6. Performing Organization Code
8. Performing Organization Report No.
10. Work Unit No,
590-14-31-01
11. Contract or Grant No.
13. Type of Report and Period Covered
Technical Memorandum
14 Sponsoring Agency Code
Paul E. McGowan: Langley Research Center, Hampton, Virginia.
Mehzad Javeed: lockheed Engineering & Sciences Company, Hampton, Virginia.
Harold H. Edighoffer: Analytical Services & Materials, Inc., Hampton, Virginia.
Pres_mted at the Fourth NASA/DOD CSI Conference, Orlando, FL
Novenber 5-7, 1990
16. Ab_ract
The status of the Dynamic Scale Model Technology (DSMT) research program is
presented. DSMT is developing scale model technology for large space structures
as part of the Controls Structures Interaction (CSI) program at NASA Langley
Research Center (LaRC). Under DSMT a hybrid-scale structural dynamics model of
Space Station Freedom has been developed. Space Station was selected as the
focus structure for DS>iT since the station represents the first opportunity to
obtain flight data on s complex, three-dimensional space structure. Included
in the paper is an overview of DSMT including the development of the space
station scale model and the resulting hardware. Scaling technology was developed
for this model to achieve a ground test article which existing test facilities
can accommodate while employing realistically scaled hardware. The model was
designed and fabricated by the Lockheed Missiles and Space Co., Sunnyvale, CA,
and is assembled at LaRC for dynamic testing. Also, results from ground tests
and analyses of the various model components are presented along with plans for
future subassembly and matted model tests. Finally, utilization of the scale
model for enhancing analysis verification of the full-scale space station is also
considered.
17. Key Words (Suggest_ by Author(s))
Scale Models
Ground Testing
Finite Element Anlaysis
Test/Analysis Correlation
Analysis Verification
19. SecuriW Cla_if. (of this repot)
Unclassified
NASA FORM 1626 OCT 86
18. Distribution Statement
Unclassified--Unlimited
Subject Category 39
20. Security Cla_if. (of this pa_)
Unclassified
21. No. of pages
3O
22. price
A03


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