Prospects of Large Deployable Reflector Antennas for a New
Generation of Geostationary Doppler Weather Radar
Satellites
Eastwood Im1, Mark Thomson2, and Houfei Fang3
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109
James C. Pearson 4 and James Moore5
ManTech SRS Technologies, Huntsville, AL 35806
and
John K. Lin 6
ILC Dover LP, Frederica, DE 19946
A novel mission concept, namely NEXRAD in Space, has been developed for detailed
monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit. This
mission concept requires a space deployable 35-m diameter reflector that operates at 35GHz with a surface figure accuracy requirement of 0.21 mm RMS. This reflector is well
beyond the current state-of-the-art. To implement this mission concept, several potential
technologies associated with large, lightweight, spaceborne reflectors have been investigated
by this study. These spaceborne reflector technologies include mesh reflector technology,
inflatable membrane reflector technology and Shape Memory Polymer reflector technology.
Nomenclature
Td
Tg
Tr
Ts
=
=
=
=
deformation temperature
glass transition temperature
recovery temperature
storage temperature
I. Introduction
U
nder NASA’s Earth Science Technology Program, a novel mission concept has been developed for detailed
monitoring of hurricanes, cyclones, and severe storms from a geostationary orbit1,2. This mission concept is
named as “NEXRAD in Space (NIS)”. NIS is designed to operate in the geostationary orbit at an altitude of 36,000
km. It would provide Ka-band (35 GHz) radar and line-of-sight Doppler velocity profiles over a circular Earth
region of approximately 5200 km in diameter with a 12-km horizontal resolution, and a minimum detectable signal
of 5 dBZ. The NIS radar achieves its superb sampling capabilities by use of a 35-m diameter in-space deployable
spherical reflector. The antenna has two transmit-receive array feeds that create a three-dimensional image of both
reflectivity and Doppler velocity inside and surrounding the storm systems approximately every 60 minutes. Both
the reflector and the spacecraft will remain stationary as the feeds perform spiral scans to 4o to cover a 5200-km
diameter circular area on the Earth’s surface.
1
Manager, Earth Science Instruments and Technology Office and Advanced Instruments Program Office, 4800 Oak
Grove Drive/MS300-243, Member AIAA.
2
Principal Engineer, Mechanical Systems Division, 4800 Oak Grove Drive / MS299-100, Senior Member AIAA.
3
Senior Engineer, Mechanical Systems Division, 4800 Oak Grove Drive / MS299-100, Senior Member AIAA.
4
Aerospace Engineer, Aerospace Technologies Directorate, 500 Discovery Drive, Member AIAA.
5
Vice President and Director, Aerospace Technologies Directorate, 500 Discovery Drive, Member AIAA
6
Lead Design Engineer, Engineering, One Moonwalker Road / MS22, Senior Member AIAA.
1
American Institute of Aeronautics and Astronautics
The mission concept requires a space deployable 35-m diameter reflector that operates at 35-GHz with a surface
figure error of 0.21 mm RMS. This reflector technology, however, is well beyond the current state-of-the-art. In
order to implement NIS, several potential technologies associated with large, lightweight, spaceborne reflectors are
being investigated. These spaceborne reflector technologies, which include mesh reflector technology, inflatable
membrane reflector technology and Shape Memory Polymer (SMP) reflector technology, will be discussed in the
following sections.
II. Mesh Reflectors
Mesh reflectors are the only types of deployable antenna reflectors that have successfully flown in space as parts
of an instrument or other satellite system. More than twenty two mesh reflectors have or will be flown by 2009 for
USA commercial and/or science missions. The largest current mesh reflector aperture is 17 meters and will be
increased to 22 meters with the launch of the MSV telecommunications satellite by 2009.
Figure 1. The 9.1-m mesh reflector for
NASA ATS-6 mission
Figure 2. 4.9-meter S-/Ku-Band dual antennas for
TDRS
Mesh reflector technology has very significant flight
heritage, Fig. 1 is the picture of the Wrap-Rib Mesh
Reflector for ATS-6 that is developed by Lockheed3. The
diameter of the reflector is 9.1 m and the RF frequency is
S-band. The ATS-6 was launched on May 30, 1974.
Figure 2 shows the Radial Rib Reflector developed by
Harris4 for NASA Tracking & Data Relay Satellite
(TDRS). Twelve TDRS Ku/S-Band antennas have been
deployed in orbit with successful operations since 19835.
Figure 3 shows the picture of the Folding Radial Rib Mesh
Reflector developed by Harris, first flown on the ACES
spacecraft in 2000 for the Garuda mobile communications
system. Meanwhile, the European and Japanese space
agencies have also developed and flown different types of
Figure 3. ACES Garuda 12-meter L-Band
mesh reflectors.
reflectors
A mesh shaping network that is typical of radially
ribbed reflectors is shown in Fig. 4. It comprises various
front & rears cords that control the position of the antenna mesh within the aperture. The cords are tensioned and
positioned by a plurality of drop and edge ties, which thusly govern the deployed surface shape of the mesh. It is by
adjustment of these cords that the required reflector surface figure is achieved.
Of all the current mesh reflector technologies the current state-of-the-art for demonstrated on-orbit stability and
surface accuracy is Northrop Grumman Space Technology’s AstroMesh reflector. Figure 5 gives a schematic view
of the AstroMesh.
2
American Institute of Aeronautics and Astronautics
The primary components of an
EDGE TIE
AstroMesh reflector6 are a flat deployable
FRONT CORD
perimeter truss, front and rear nets, tension
ties, and mesh. The front and rear nets are
composed of high stiffness, near-zero CTE
NOTE: MESH NOT SHOWN FOR CLARITY
composite web elements that form two backto-back geodesic domes. One of the domes is
shaped to approximate the required parabolic
surface metric with triangular facets. The
webs are tensioned to high stress levels by
even application of normal loads from the
REAR CORDS
tension ties. These high stress levels allow
DROP TIES
the front net to maintain very high stability
Figure 1. Typical radial-rib mesh shaping network
and precision despite parasitic mesh loads.
The structural behavior of the nets is such
that near zero mechanical pillowing of the
mesh is experienced, so that far fewer drop
ties are required than by the typical radial rib
reflector. The flat truss is relatively deep and
is composed of near-zero-CTE carbon fiber
composite. This deep truss is very stiff and
highly thermally stable.
Five AstroMesh reflectors have been
deployed on commercial spacecraft since
2000. Two are on Thuraya spacecraft (see
Fig. 6) which were launched in October 2000
and June 2003. Both Thuraya spacecraft
have 12.25-meter aperture reflectors. The
MBSat spacecraft (see Fig. 6) was launched
Figure 5. Schematic view of the AstroMesh reflector
in March 2004 with a 12-m AstroMesh
reflector on board. Two 9-meter AstroMesh
reflectors are on Inmarsat 4 (see Fig. 6) spacecraft which were launched in April 2005 and October 2005.
The antenna mesh that comprises the reflective surface of all current deployable mesh reflectors is evenly
stretched across the aperture. Mesh is typically made of extremely fine gold-plated molybdenum wire that is Tricot
knitted thus making it highly elastic, which allows it to yield to the structural definition provided by the reflector
structures. Noteworthy advantages of using mesh include its ability to be arbitrarily packaged in an extremely small
volume without introducing any permanent plastic deformations, its extremely low areal mass, high stability and
longevity in a space environment. With minor development effort mesh will be capable of excellent RF reflectivity
and cross-pol performance to at least the 35 GHz band required by the NEXRAD instrument.
Figure 6. Thuraya spacecraft, MBSat spacecraft and Inmarsat 4 spacecraft
The deployable reflector structures that support mesh, however, will require significant development to be able
to support the required surface accuracy of 0.21 mm. The best mesh reflector surface accuracy that has been
demonstrated thus far, in terms of the ratio of aperture diameter (D) to surface accuracy (δRMS) is in the vicinity of
D/δRMS = 20,000 to 30,000. Extrapolation from the theoretical study given in reference 7 leads us to conjecture that
the maximum possible value of D/δRMS for a passively maintained reflector structure is well below D/δRMS =
100,000.
3
American Institute of Aeronautics and Astronautics
Because the NIS Goal for D/δRMS = 170,000
the mesh reflector that successfully supports this
mission must offer in-flight adjustment of the
surface figure. Whether this control is fully active
with short update periods or more quasi-static in
nature has yet to be determined. Nonetheless, an
appropriate reflector surface metrology system
with feedback and control of the mesh surface
shaping structure will be required7.
To achieve surface figure control to 0.21 mm
RMS during the orbit the contour of mesh can be
controlled by changing the lengths of the tie
elements, whether it is the drop ties of a radial rib
reflector or the tension ties of the perimeter truss.
With advancements in miniature actuator
technologies potentially appropriate linear
actuators for this application are readily available.
Figure 7 shows a miniature actuator8 that could be
Figure 7. Piezoelectric linear micro-actuator
used to change the length of a tie assembly for
surface shape control. This and other similar approaches are being considered by the NIS project for application to
mesh reflectors.
III. Inflatable Membrane Reflector
As with terrestrial radio frequency (RF) communications, future RF communications for space are trending
towards large aperture and high frequency antennas. Transporting these large aperture antennas into space and then
operating them creates a need for a low packaging factor (stowed volume / deployed volume) and a low areal
density (aperture mass / aperture area) while also demonstrating the sub-millimeter surface shape accuracy that is
required for Ka-band. While conventional antenna design technologies have advanced and are now capable of
larger apertures and higher frequencies, they still possess some implicit properties that may limit the areal density
and packaging factors. Furthermore, achieving and maintaining precision shape following deployment represents
another new set of challenges for conventional designs. Hence, there is a need to continue development of other
enabling technologies, such as inflatable thin film antennas, that may offer better solutions to these issues.
During the last two decades, SRS has partnered JPL, NASA, Air Force, and large defense contractors to develop
inflatable thin film concentrators. Initially these concentrators were designed to concentrate sunlight as a heat
source for solar thermal propulsion systems. Later, these same designs were modified to concentrate sunlight for inspace solar power generation. More recently, and more prominently, these designs have been modified to function
as transmit / receive antennas with both in-space and terrestrial applications. SRS has fabricated and tested on-axis
and off-axis parabolic geometries with apertures up to 10m. Lightweight inflatable structures were developed to
support these antennas including inflatable tori, that support the periphery, and inflatable radomes, that encapsulate
the antenna while supporting the periphery.
A. Design / Fabrication Approach
A typical inflatable antenna consists of two thin films, a reflector and a canopy, that are joined around the edges.
The relatively thin (<1-mil) polymer films are cast on a precisely shaped mandrel and then thermally cured and
released. The reflector film is typically metalized with a vapor deposited silver or aluminum coating, nominally
very thin. The membranes are then joined using a leak tight bonding technique. Following fabrication, the antenna
is integrated with an inflatable torus or radome via compliant features that minimize loading changes associated with
thermal excursions. Figure 8 shows a typical inflated antenna design. The antenna and torus structures are precisely
inflated to approximately achieve the desired membrane stress and structural stiffness. Then, the boundary tension
is adjusted to achieve the best shape. While the reflector film and canopy film are cast as one piece polymer thin
films with a parabolic shape, achieving high surface accuracy after inflation deployment and in the space thermal
environment is more challenging. Inflation pressure and film stress introduce shape errors, especially slope error
near the edges (characteristic Hencky (W Error)). Thermal loads cause less systematic shape errors. The thermal
induced shape errors can be significant and may drive the need for active control of the inflatable antenna.
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American Institute of Aeronautics and Astronautics
However, recent improvements in low coefficient of thermal
expansion space ratable polymers can potential reduce the
magnitude of thermal distortions9.
B. Recent Inflatable Thin Film Antenna Technology
NASA and SRS Technologies have successfully
collaborated on research and development of lightweight
thin-film antennas. To date, on-axis, off-set, and Cassegrain
antennas, from 0.3m to 4m in aperture, have been designed,
fabricated, and radio frequency (RF) characterized via range
testing10. The designs address requirements for space based
systems as well as inflatable terrestrial radome antennas.
Fixed, deployable, and adaptive test structures are being
developed to support the thin film antennas during testing
and future operations. RF characterizations of off-set and
on-axis antennas have been performed in the NASA GRC
Far Field and Near Field facilities at frequencies from Xband to Ka-band. Thus far, frequencies through Ku-band
have indicated excellent antenna performance. Ka-band test
results indicate that improved antenna surface shape accuracy
(sub-millimeter values) is required for efficient operation.
Thus, shape optimization, tooling technology, fabrication
processes, and active shape control techniques are being
Figure 8. 4mx6m Off-Axis Inflatable Antenna
considered to enable Ka-band operations.
All of this successful lightweight inflatable thin-film
antenna research and development has the potential to
enhance current RF communications capabilities and enable many future RF requirements that need efficiently
packaged deployable antennas with large apertures. Figure 9 shows RF characterization data from the 4mx6m
testing. This data demonstrates the X-band antenna performance while showing the need for shape improvement to
extend performance to Ka-band.
Figure 9. 8.4 GHz Data for 4m x6m Test Article (676 Measure Efficiency)
C. Recent Adaptive Antenna Work
There are a number of technical challenges for large inflatable thin film antennas. The primary challenge is
shape errors reduction to enable Ka-band and other higher frequency applications. The shape errors are the result of
inflation pressure (membrane effects including Hencky W-error, oil can, other boundary errors) and thermal
distortions. Key technologies being developed to address the challenges include: 1) improved membrane materials,
2) active control and 3) improved tooling and manufacturing processes.
5
American Institute of Aeronautics and Astronautics
A membrane with an initially parabolic shape assumes a characteristic error when subject to inflation loads.
This error, known as Hencky or W error, can be corrected with passive means. One possible solution is tailored
membrane thickness or reflective coating stress distribution. This has been demonstrated for optics on meter class
structures. SRS has demonstrated this with a membrane optic as shown in Fig. 1011.
Another possible solution is initial shape optimization, which has been demonstrated for large scale apertures for
correction of classic Hencky Error and other static boundary errors. Figure 11 shows a model of an on-axis thin film
with the W error.
hC (R ) = h0 + h2 ( kR ) 2 + h4 ( kR ) 4 + h6 ( kR ) 6
10 Inch Test Article with Variable Coating
Figure 10.
Nonlinear coating Prescription for Parabolic Shape
developed by Mike Wilkes (AFRL)
Variable Coating Thickness to Correct W Error
Initial tooling mandrel shape optimization is another way to
correct errors. SRS has both modeled and demonstrated this
technique. Figure 12 shows that optimizing mandrel shape
significantly improves reflector shape while advanced high
temperature tooling enables fabrication of optimized membrane
apertures12.
Thermally induced shape aberrations are also significant.
Resulting shape errors can be large (for example, 13.9 mm for a 25
meter polyimide antenna in geosynchronous orbit)13. Static shape
optimization alone is not an option for inflatable antenna made from
the current generation of space rated polymer materials under most
operational scenarios. Possible solutions include low or zero CTE
membrane materials and / or active shape control. As shown in Fig.
13, reduced CTE materials can help enable very large ultra-light
deployable apertures for high band width communications, space
science, earth science, and other applications.
Figure 11. Model of 23 Meter Thin
Film Antenna with Characteristic Shape
Error
Shape Error Along Major Axis
0. 300
0. 250
0. 200
Initially Parabolic
0. 150
Shape
Optimized Design
(Biased mandrel)
0. 100
0. 050
0. 000
80. 000
60.000
40.000
20.000
0.000
-20.000
-40. 000
-0.050
Film Thickness - .001”
Pressure - .022” H2O
High Tension Case
Figure 12.
Shape Correction via Tool Optimization
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American Institute of Aeronautics and Astronautics
-60. 000
-80. 000
Adaptive control strategies and/or advanced signal processing is another way to control errors in thin film
antennas. Under a technology development program SRS and Northrop Grumman performed a 5m feasibility demo
and successfully demonstrated a method for using electrostatic forces to control the shape of a lightweight
deployable membrane aperture14. A high voltage power supply and control system, large dynamic range shape
control, and statically stable electrostatic control. An example of shape correction for pressure and -150Co
temperature change is shown in Fig. 14. Active controls can provide additional flexibility and reduce risks
associated with modeling errors and environmental unknowns. It offers potential for morphing antenna technology
to optimize aperture for different functions. Adaptive antenna concepts can meet the density (<2kg/m2), power
(<200 Watts ), and size (>20m diameter) characteristics desired for future Ka and higher band systems. Key
technologies for adaptive control includes: 1) integration of reflector with light weight deployable reaction structures
for electrostatic control or 2) development of in plane surface actuation technology using piezoelectric patches or
other surface strain approaches, and 2) improved materials with low CTE and low modulus, and more durable RF
coatings or RF reflective polymers.
Shape error of 5-meter CP1 reflector
caused by partial shading (i.e. thermal)
Figure 13.
Reduced CTE materials required to enable
very large ultra-light deployable apertures for
high band width communications, Space
Science, Earth Science, and other applications
Low CTE Data
D. Current Work
Under a current effort an actively controlled inflatable reflector is being designed to demonstrate this technology
for future applications such as the NIS antenna. This work includes advanced material studies, the design and
fabrication of an inflation control system, manufacturing of the inflatable antenna, and integration with a test support
ring. The test article will use piezoelectric surface actuators to demonstrate the ability to achieve Ka band accuracy
under dynamic thermal loads.
Uncorrected 3.42 RMS Error mm
Figure 14.
Corrected .0052mm RMS Error
Modeled Results for 29 Channel Electrostatic Control
Current activities are also focusing on improving materials for future inflatable antenna applications. Materials
under development by SRS Technologies include metal filled polymers that are RF reflective. This material could
improve the thin film antenna manufacturing process by eliminating the need for coating the polymer film with an
RF reflective material. Although effective, the coating process is expensive, time consuming, error prone, and
presents particular challenges for large apertures (generally >2m) due to handling fixtures and facility limitations.
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American Institute of Aeronautics and Astronautics
The metal filled RF polymer will simplify the manufacturing process and provide an effective RF reflective coating.
These RF reflective polymers are also incorporating new polymer formulations that significantly reduce the
coefficient of thermal expansion of the material. Silver filled polyimides have been fabricated that perform
comparably with vacuum deposited aluminum coated materials.
As requirements for antenna size and accuracy continue to increase new technologies must be developed to meet
these requirements. Inflatable antenna technology offers the maximum packaging efficiency and a simple reliable
deployment method. The inflatable technology offers a solution to aperture requirements >25 m where other antenna
technologies begin to be limited by launch vehicle volume and mass restrictions.
IV. Shape Memory Polymer Reflector
Rigidizable materials in general are materials that are initially flexible to enable system packing and deployment,
and become rigid when exposed to an external stimulus15. Although many types of rigidization mechanisms exist,
this section will deal with thermally activated Shape Memory Polymer (SMP) composite materials and structures for
antenna reflector applications. The effect of shape memory can be triggered by a stimulus other than temperature
such as light or chemicals and these are classified as photo responsive and chemical responsive shape memory
respectively. By definition, thermally activated shape memory polymers are polymers that can be predetermined to
regain their original cured shape after being packed or deformed above their glass transition temperature by applying
an external thermal influence. The SMP polymers differ from the traditional thermoplastic polymers in their ability
to restore to their original shape by mere application of heat. To date, SMP have been demonstrated to recover more
than 99% of their original shape in most applications if they are not under the influence of an external mechanical
load.
The thermo-mechanical response of a thermally activated SMP can be characterized by four critical
temperatures16. The glass transition temperature, Tg, is the transition point for thermo mechanical deformation and
recovery. Polymers possessing a glass transition temperature exhibit rubbery characteristics above Tg and exhibit a
glassy state below Tg. The deformation temperature, Td, is the temperature at which the polymer can be deformed
into a temporary shape. Td can be above or below Tg, but for folding or packing purpose it is not recommended to
tightly fold SMP below Tg. The folding temperature for this class of SMP is typically 20°C above Tg. The storage
temperature, Ts, is lower than Tg and denotes the temperature at which the polymer is stable in the packed or
deployed state over long period of time. Finally, the recovery temperature, Tr, is the temperature at which the
original shape is recovered.
The manufacturing methods for SMP composite structures are similar to the traditional thermoset composites.
The desired final shape of the SMP composite structure is set during its initial cure cycle at an elevated temperature.
Once the SMP material is completely cured, it can be reheated to a minimum of 20oC above the Tg where it becomes
flexible and can be tightly folded. The flexibility of the SMP composite at the folding temperature depends on the
properties of both the resin and the fiber. After the material is folded, it can be constrained in that position and then
cooled to approximately 15oC below Tg or Ts at which point the SMP composite can be unconstrained and will
remain frozen in the folded position until it is heated again. When the SMP is heated to the recovery temperature
after being folded, the SMP material will naturally begin to return to its initial cured shape based on the shape
memory recovery force of the composite. In actual applications, although the composite has a higher shape memory
recovery force than the shape memory polymer resin alone, inflation gas is often required to augment the structure’s
return to its originally cured shape. Recently test has been conducted on this SMP composite material and results can
be found in several published papers17,18.
Shape memory polymers have been widely used in the commercial and medical fields with well known
performance heritage. Some examples of biomedical applications are artificial muscles, catheters, wire mesh stents
and other human interface devices. However, to date, shape memory polymers have only seen limited applications
in space systems, but a number of applications are under development. These applications include structural
components such as composite tube structures, reflector dish structures, and hinges. Several systems under
developed are for very large truss or boom structures. In structural applications where large system payload mass is
part of the deploying structure the limited recovery force available from the SMP is not sufficient to deploy the
system. Therefore, some form of force augmentation is required to deploy the system. One option is to use inflation
pressure inside the SMP structure to assist with the deployment. For precision structures where the fibers must be
properly strained to remove all packing deformities, the use of inflation deployment offers the benefit of accuracy.
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American Institute of Aeronautics and Astronautics
SMP composite materials have recently been utilized for investigation on a number of development programs for
space applications. Four such programs that can directly benefit the development of large deployable antenna
reflector are discussed below. These programs include SMP booms and truss structures and SMP antenna reflectors.
Figure 15.
SMP composite truss application in deployed and packed configurations
SMP cylindrical booms of various sizes (from 10 mm to 100 mm in diameter and 1-meter to 5-meter in length)
have been extensively tested under NASA, DARPA and IRAD programs in the past few years at ILC Dover. The
technical readiness levels of these booms are at 5 to 6 and they have also been assembled into truss structures for
packing, deployment, structural, mechanical and thermal properties evaluations. The truss structure shown in Fig.
15 was fabricated from 1.5-m long, 45.7-mm diameter 2 ply IM7/SMP booms. This type of truss structures
designed using SMP composites has demonstrated deployed-to-packed length ratios of 100:1. Truss structures like
this can be used to construct the back support structure (struts and perimeter trusses of various shape) for large
lightweight space based antenna reflectors.
Figure 16.
JHU/APL Hybrid Inflatable Antenna 2-Meter SMP Composite Reflector
SMP composite materials have also been used to manufacture deployable parabolic reflector dishes. The use of
this technology is currently planned for JHU/APL’s Hybrid Inflatable Antenna19 and JPL’s Advanced Precipitation
Radar Antenna Singly Curved Parabolic Antenna Reflector20. For the Hybrid Inflatable Antenna, a 2-m diameter
SMP composite reflector was recently fabricated and assembled into a toroidal support structure to demonstrate
feasibility of the technology (Fig. 16). For this application, both the reflector dish and the support torus are
envisioned to be fabricated from the SMP composite. To date, packing and deployment trials have not been
demonstrated on the 2-m reflector, but two 0.5-m reflectors were fabricated from a carbon/SMP composite to
demonstrate a potential folding scheme (Fig. 17).
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American Institute of Aeronautics and Astronautics
The same carbon/SMP composite has also been
used to fabricate the Singly curved parabolic
antenna models for feasibility study. These antenna
models are 1/10th scale of the actual application with
a length and width of approximately 0.5-m. After
cure, a vapor deposited aluminum (VDA) polyimide
film was bonded to the inner surface of the antenna
to increase its reflectivity.
For packing and
deployment demonstration, the reflector was heated
in an oven to above glass transition temperature for
packing (in this case it was rolled, see Fig. 18).
After the antenna was packed it was taken out of the
Figure 17. 0.5-meter SMP Composite Reflector
oven and allowed to cool in the rolled up shape.
Then it was placed back in the oven for deployment
by the material’s shape memory return function only. This shape memory return feasibility test was qualitatively
successful and further work is continuing in this area to work on the details of scaling this technology up to larger
size antennas and quantitatively measure the shape memory recovery response of the composite.
SMP material technology can be further developed for ultra lightweight reflector by applying innovative
composite fibers in both weave construction and material with the SMP polymers. Ultra lightweight SMP reflectors
can be supported by SMP trusses to construct large reflectors in space.
Figure 18. 0.5-m SMP Composite Singly Curved Parabolic Reflector Deployed and Packed
Configurations
V. Conclusions
In order to implement the NIS mission concept, several potential technologies associated with large, lightweight,
spaceborne reflectors have been investigated and discussed by this paper. These spaceborne reflector technologies
include mesh reflector technology, inflatable membrane reflector technology and Shape Memory Polymer reflector
technology. Mesh reflector technology has a very rich flight heritage and is very promising to be developed for the
NIS application. Inflatable antenna technology offers the maximum packaging efficiency and a simple reliable
deployment method. The inflatable technology offers a solution to very large apertures where other deployable
reflector technologies begin to be limited by launch vehicle volume and mass restrictions. SMP material is a new
type of material which has very unique and desirable characteristics. It is being developed rapidly and also has the
potential for the NIS reflector application. Another major issue associated to the NIS 35-m reflector is how to
maintain the 0.21-mm RMS surface contour precision requirement. It is concluded by previous studies that active
surface shape control for the 35-m deployable reflector is necessary and several studies have been initiated21,22.
Acknowledgments
Authors would like to express the appreciations to Ubaldo Quijano and Gregory Davis of JPL for their help and
support. The work described was performed at Jet Propulsion Laboratory, California Institute of Technology,
ManTech SRS Technologies, and ILC Dover LP under a contract with the National Aeronautics and Space
Administration.
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American Institute of Aeronautics and Astronautics
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Scarborough, S.E. and Cadogan, D.P., “Applications of Inflatable Rigidizable Structures,” SAMPE Symposium, Long
Beach California, 2006.
18
Scarborough, S.E. and Cadogan, D.P., “Rigidzable Materials for Inflatable Space and Terrestrial Structures,” SAMPE
Symposium, Long Beach California, 2005.
19
Willey, C, Bucolic, R, Skulney, W, Cadogan D.P., Lin, J.K., The Hybrid Inflatable Antenna (AIAA 2001-1258), 42nd
AIAA/ASME/ASCE/AHS/ASC SDM Conference, 2001.
20
Lin, J.K, Sapna, G.H., Scarborough, S.E., Lopez, B.C., “Advanced Precipitation Radar Antenna Singly Curved Parabolic
Antenna Reflector Development,” AIAA-2003-1651, 44th AIAA/ASME/ ASCE/AHS/ASC Structures, Structural Dynamics, and
Materials Conference and Exhibit AIAA Gossamer Spacecraft Forum, Norfolk, VA, April 7-10, 2003.
21
H. Fang, M. J. Pattom, K. W. Wang, E. Im, “Shape Control of Large Membrane Reflector with PVDT Actuation”, AIAA2007-1842, 48th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Honolulu, Hawaii,
April 23-26, 2007
22
H. DeSmidt, K. Wang, H. Fang, “Gore/Seam Cable Actuated Shape Control of Inflated Precision Gossamer Reflectors –
Assessment Study”, AIAA-2006-1902, 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials
Conference, Newport, Rhode Island, May 1-4, 2006.
11
American Institute of Aeronautics and Astronautics