Modular antenna construction can provide a significant increase in reflector aperture size over deployable reflectors. The modular approach allows reflective mesh surfaces to be supported by a minimum of structure. The kinematics of the selected deployable design approach were validated by the subscale demonstration model. Further design refinements on the module structural/joints and design optimization on intermodule joints are needed

Woods, A. A., Jr.

English

NASA Technical Reports Server

A MODULAR APPROACH TOWARD
EXTREMELY LARGE APERTURES
A. A. Woods, Jr.
Lockheed Missiles and Space Company
Sunnyvale, California
Large Space Systems Technology
Second Annual Technical Review
Langley Research Center
Hampton, VA
November 19, 1980
121
https://ntrs.nasa.gov/search.jsp?R=19810010678 2020-03-21T09:27:14+00:00Z
STUDY OBJECTIVES
A nine month study entitled "Development of a Deployable Module Concept
for Large Reflector Application" was undertaken by Lockheed Missiles and
Space Company, Inc., in September 1979. This contract was originated by
Langley Research Center as a subtask of an ongoing contract in support of the
development of Large Space Structures Concepts.
The subtask objectives are summarized in Figure I. LMSC was to design a
large erectable antenna using a deployable modular approach and characterize
the performance of such antennas. In addition, the module deployment kine-
matics were to be verified by construction of a working subscale demonstration
model, and on-orbit antenna assembly scenarios were to be investigated.
• DESIGN A DEPLOYABLE MODULAR STRUCTURAL
ELEMENT FOR ANTENNA APPLICATIONS
• CHARACTERIZE PERFORMANCE
• VALIDATE KINEMATICS
• INVESTIGATE ORBITAL OPERATIONS
Figure i
122
The f i n a l  product  envis ioned  from t h e  s tudy  w a s  a l a r g e  p a r a b o l i c  r e f l e c -  
t o r  t o  b e  e r e c t e d  i n  lower e a r t h  o r b i t  from up t o  330 s e p a r a t e  deployable  mod- 
u l e s  t r a n s p o r t e d  by one STS launch. This concept is overviewed i n  F igure  2.  
Figure 2 
123 
DESIGN REQUIREMENTS
The design constraints established for the study are listed in FiEure 3.
Each module was to be an autonomous deployable unit, attached to neighboring
modules through three attachment points. Each module was to provide a hex-
agonal RF reflective surface element, independent of but adjacent to neigh-
boring elements. The modules were to provide minimum stowed volume (maximize
packing efficiency) and be capable of being deployed by an external, plug-in
deployment power device.
• EACH MODULE AN AUTONOMOUS STRUCTURE
• HEXAGONAL SURFACE ELEMENT
• ORBIT DEPLOYMENT ACCOMPLISHED WITH EXTERNAL AID
• THREE POINT MODULE TO MODULE ATTACHMENT
• MINIMIZE STOWED VOLUME
Figure 3
]24
DESIGNAPPROACH
The design approach selected to satisfy the foregoing requirements con-
sists of a reflective meshsurface supported by a small diameter (1.27 cm)
thin wall (.4 mm)tubular framework. Several of the tubes contain spring
powered, latching joints which allow them to be folded to reduce the stowed
package size. A single central jackscrew controls all of the deployment
motions, acting as both the slider link of a four bar linkage for the upper
truss and as a cable reel to deploy cables which control the deployment
motions of the lower structure elements. The stowed module is basically a
passive device, in that external mechanical power must be supplied by a motor
for deployment to occur.
• SURFACE
• FRAME
• STRUCTURE
• JOINTS
- FOLDING HEXAGONAL TRUSS PLATE
- FOLDED TRIANGULAR TRUSS
- 1.27 CM DIAMETER, 0.4 mm THICK GRAPHIC
EPOXY TUBES
- SELF ACTIVATING AND LOCKING WITH TWO
DEGREES OF FREEDOM
DEPLOYMENT CONTROL - CENTRAL JACK SCREW WITH STRUCTURAL
AND CABLE SYNCHRONIZATION
DEPLOYMENT POWER - EXTERNAL PLUG IN MOTOR
Figure 4
125
MODULEDESIGNOVERVIEW
Figure 5 describes the basic componentsof a single module. An upper
hexagonal truss frame supports the mesh, and structural depth is provided by
a triangular lower frame cross braced to the upper frame. The folded truss
elements use spring powered latching joints which provide continuous column
stiffness in the deployed position. Deployment is effected by a central jack-
screw in the upper space frame which opens the hexagonal frame through a four-
bar linkage and simultaneously pays out cables which control the spring pow-
ered deployment motions of the lower frame members. The jackscrew is powered
by a separate, plug-in motor unit which is used to deploy all individual mod-
ules.
PERIMETER ARMS
UPPER TRUSS ARMS
REFLECTOR
SURFACE
LOWER TRUSS ARMS
CROSS
BRACES
DEPLOYMENT
JACKSCREW
LOWER ARMS
Figure 5
126
Figure 6 shows the subscale demonstration model in the stowed position. 
The stowed package is approximately 25 cm in diameter by 100 cm long. 
separate deployment motor housing can be seen as a small rectangular box ex- 
tending below the module. 
The 
Figure 6 
127 
Figure 7 shows t h e  demonst ra t ion  model e a r l y  i n  i ts deployment cyc le .  
The c ross  b races  are moving outward and upward and t h e  hexagonal  t r u s s  is 
beginning t o  open. 
128 
Figure  7 
Figure  8 shows t h e  model f u r t h e r  along i n  i t s  deployment motion. The 
upper s u r f a c e  has  opened s u b s t a n t i a l l y  and t h e  c r o s s  b race  c e n t e r  j o i n t s  have 
reached t h e  peak of t h e i r  upward swing. 
F i g u r e  8 
129 
Figure 9 shows t h e  model s t i l l  f u r t h e r  a long  i n  i ts deployment. The 
c r o s s  brace lower j o i n t s  are s e p a r a t i n g  from t h e  upper j o i n t s  deepening t h e  
s t r u c t u r e .  
Figure 9 
The f u l l y  deployed module is  p i c t u r e d  i n  F igure  10. This  demonst ra t ion  
model measures approximate ly  160 cm a c r o s s  t h e  co rne r s  of t h e  hexagonal re- 
f l e c t o r  s u r f a c e  and s t a n d s  approximately 135 cm high .  The tub ing  s i z e  (1.27 
cm diameter) and t h e r e f o r e  j o i n t  s i z e s  are f u l l  scale i n  t h e  model. For a 
f u l l  scale module, however, t h e  tube  l e n g t h s  a r e  inc reased  t o  t h e  f u l l  l e n g t h  
of t h e  STS O r b i t e r  cargo  bay, r e s u l t i n g  i n  a f l i g h t  module measuring 28 meters 
a c r o s s  t h e  c o r n e r s  of the hexagonal s u r f a c e  by 24 meters deep. 
F igure  10 
131 
PERFORMANCE STUDIES
Figure Ii shows the mass of individual modules of various sizes. As the
module size increases, the essentially parasitic mass of the module structure
and the deployment mechanism becomes less and less significant and the module
mass becomes predominantly the mass of the reflective mesh.
MODULE
MASS
Kg
8O
6O
4O
20 -
0 I I
10 20
MODULE DIA (M)
Figure ii
REFLECTIVE
SURFACE
STRUCTURE
DEPLOYMENT
MECHANISM
I
30
132
Figure 12 demonstrates this effect more clearly. For small modules (i0
meters in diameter) the reflective mesh surface, which is for an antenna re-
flector the useful portion of the module, amounts to a little over one third
of the total mass of the module. For a 28 meter diameter module, however,
the mesh surface comprises almost two thirds of the mass of the module.
100
MASS
FRACTION
(%)
8O
60
40 -
20 -
0 I I
10 20 30
MODULE DIA (M)
Figure 12
133
DEPLOYABLE MODULAR ANTENNA APPLICATION
The structural efficiency of modular antennas is fully realized in large
aperture uses at moderate to mm wavelength RF frequencies. Modular antennas
can be efficiently utilized through the majority of currently projected radio-
metry and ODSRS reflector applications when multiple shuttle flights are con-
sidered. Even with a single shuttle, the modular approach yields a signifi-
cant potential for performance improvement over the current projections for
mesh deployables as can be seen in Figure 13.
I
>-
u
z
LU
C7
W
n,"
U.,
10o0
400
200
100
80
60
40
2O
10
8
6
4
RADIO
ASTRONOMY
-PROJECTED
MESH DEPLOYABLE
CAPABILITY
-(REF. RUSSELL,
CAMPBELL, FREELAND)
0.5 I I I I I
2 4 6 8 10 20
VLBI
SETI
I I I I
40 60 80100
DIAMETER - M
Figure 13
I o STS
I
3 STS
I
2 STS
I
I STS
I
,I I I I J
200 400 1000
='---- -- MESH
SURFACE
MEMBRANE
SURFACE
134
MODULAR ANTENNA ASSEMBLY METHODS
Figure 14 summarizes the various reflector assembly scenarios investi-
gated during the study.
Techniques which were examined ranged from those requiring present tech-
nology STS operations with no EVA to large aperture techniques requiring de-
velopment of a self contained, automated free flying assembly satellite.
• STS CONTAINED WITH 2 RMS
• RMS/ARTICULATED BOOM FIXTURE
• FORMATION FLYING SATELLITE
• FREE FLYING AUTOMATED SATELLITE
Figure 14
135
Reflectors of moderate size (up to approximately 70 m diameter) can be
assembleddirectly from the Orbiter cargo bay using 2 RMSarms. Onearm is
used to hold and position the partially completed reflector and the other arm
is used to deploy each individual module and attach it to the assembly. The
entire operation can be controlled by the payload specialist working at the
aft flight deck of the Orbiter. This concept is overviewed in Figure 15.
Figure 15
136
Figure 16 depicts assembly of a larger reflector using an articulated,
extendable boomto hold the reflector for assembly. This boomis operated
from inside the orbiter and is used to rotate and position the reflector to
receive each module. The modules are deployed and assembled to the reflector
by the Orbiter RMS. Reflector apertures up to approximately 310 meters in
diameter can be assembled in one launch using this approach.
Figure 16
137
Large aperture antennas can be assembled only by using techniques which
allow multiple resupply by the STS. One such technique is shown in Figure 17.
A free flying satellite is carried to orbit with the first set of modules.
After these modules are installed, the Orbiter releases the satellite and re-
turns to Earth. SubsequentOrbiter flights rendezvous with the satellite to
deliver and install additional modules.
Figure 17
138
Figure 18 describes another reflector assembly approach for apertures
requiring multiple STS launches. In the scheme, the satellite is a totally
automated, self contained assembly platform. The STS ferries cargo loads of
modules to orbit and delivers them to the satellite. Positioning equipment,
permanently mounted on the satellite, removes the modules from their transport
cannister, deploy them and attach them to the reflector.
Figure 18
139
SIZE LIMITS OFASSEMBLYTECHNIQUES
Figure 19 summarizesthe reflector size limitations of the various
assembly techniques. The approach using the RMSarms from the shuttle
Orbiter is limited by the reach of the two arms, allowing a maximumsize
reflector of approximately 73 m diameter. The articulated boomcase is
limited in size by the numberof modules that can be carried in the Orbiter
cargo bay, with part of the volume taken up by the stowed assembly boom.
The assembly satellite cases are essentially limited in size only by a number
of shuttle launches devoted to the task.
• STS CONTAINED - 73 M DIAMETER
• RMS/BOOM - 310 M DIAMETER
• FORMATION SATELLITE - UNLIMITED
• AUTOMATED SATELLITE - UNLIMITED
Figure 19
]40
STUDYCONCLUSIONS
The conclusions reached during the study are summarized in Figure 20.
Modular antenna construction can provide a significant increase in reflector
aperture size over deployable reflectors. The modular approach allows re-
flective meshsurfaces to be supported by a minimumof structure. The kine-
matics of the selected deployable design approach have been validated by the
subscale demonstration model. Further design refinements on the module
structural/joints and design optimization on intermodule joints are needed.
@
MODULAR CONSTRUCTION PROVIDES A SIGNIFICANT
INCREASE IN APERTURE SIZE
APPROACH YIELDS A MINIMIZATION OF STRUCTURAL
WEIGHT
KINEMATICS ARE VALID
JOINT AND INTER MODULE ATTACHMENT REQUIRE
ADDITIONAL ACTIVITY
Figure 20
141
AREAS FOR FURTHER CONSIDERATION
The study concluded that work in two additional technology areas would
be beneficial in developing larger reflector apertures. These study areas
are surmnarized in Figure 21. The first area is the development of a larger
deployable element, perhaps seven individual modules packaged and inter-
connected to be deployed as a single unit. These large "building block"
elements would then be assembled in essentially the same manner as the single
modules.
The second area for research is the development of an active reflective
surface, that is, surface which automatically adjusts itself on orbit to
compensate for mechanical assembly tolerances and/or reflector distortions
due to thermal gradient or positioning dynamic effects.
DEVELOPMENT OF A MODULAR BUILDING BLOCK
- 100 M DIAMETER BASIC ELEMENT
- MULTIPLE MODULE INTERCONNECTED
- DEPLOYED WITH SINGLE ACTUATOR
- ABILITY TO INTERCONNECT WITH OTHER 100 M
ELEMENTS TO OBTAIN DESIRED SIZE
DEVELOPMENT OF ACTIVE SURFACE ELEMENT
- PRECISION HEXAGONAL SURFACE ELEMENT
- ORBITAL ATTACHMENT TO SUBSTRUCTURE
- ATTACHMENT THROUGH ACTIVE CONTROL
ACTUATORS
Figure 21
142
REFERENCE
Russel, R.; Campbell, T.; and Freeland, R.: A Technology Development Program
for Large Space Antennas. Paper No. IAF-80A33, 31st International Aeronau-
tical Congress of the International Astronautical Federation, Sept. 1980.
143


A modular approach toward extremely large apertures

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