Special Feature

Tendon-reinforced Ultralight Large
Antenna Reflector
Satoshi Harada†, Akira Meguro, and Masazumi Ueba
Abstract
We have been investigating an ultralight large antenna reflector with an aperture diameter of more than
20 m and total mass of 130 kg including a boom structure and holding/release structures. This reflector
is a geodesic cable network structure supported by a tendon-reinforced structure. Previous studies using
a conceptual model showed that such large antenna reflectors seemed feasible. In this article, we clarify
important design parameters, such as the catenary ratio and number of facets, to improve the manufacturability. Using detailed designs, we estimate the total weight and stowed size to clarify system compatibility.

1. Introduction
One direct way of enhancing the performance ofsatellite communication, broadcasting, interplanetarycommunication, and information gathering systems
is to increase the size of the satellite antenna reflector
because this improves the transmitting and receiving
performances even if the satellite power system andtransponder performance are not changed. Development programs for communications satellites have,over the last 20 years, yielded remarkably advanced
reflector structures, and several structural concepts
have been proposed by various organizations. Theseadvances support the cellular phones and high-speed
Internet connections being demanded for the nextgeneration of satellite communications by users on
aircrafts and trains. Unfortunately, the capital costs ofconstructing advanced satellite systems using conventional technologies are excessive. Our solution isthe combination of an ultralight large antenna reflector and a 100-beam-class multibeam feed system toconstruct a 1-Gbit/s, 1- or 1.5-ton-class satellite bus.
This article describes a design methodology for
ultralight large antenna reflectors with aperture diameters larger than 20 m and an areal density of less than
0.25 kg/m2. The target of the total mass is 130 kg† NTT Access Network Service Systems Laboratories
Yokosuka-shi, 239-0847 Japan
Email: harada.satoshi@lab.ntt.co.jp

70

including the boom structure and holding structure.
Although, the Astro-Mesh [1], [2] is now providing
large reflectors with a diameter of 13 m, and anenhanced version is being studied, the stowed size is
too large to suit 1- or 1.5-ton-class satellite buses andthe areal densities seem to be twice the required
value.
To obtain an ultralight large antenna reflector, we
propose a geodesic cable network structure supported
by a tendon structure. First, we explain our target andthe structural concept of the reflector. Experiments on
a breadboard model were carried out to ensure feasibility. Next, we examine the relationship between the
total mass and strength of the support structure so as
to detail the structural design. We determined thecable-mesh structure that achieves the required
design values given current manufacturing capabilities. To validate the proposed reflector, we clarified
detailed candidates for hinges, linkage mechanisms,
drive mechanisms, and stowed configurations of thebasic structure. The total mass of the entire structure
and the stowed configuration were examined toassess system compatibility.
2. Antenna reflector targets
Given the system frequency bandwidth of 35 MHz,meeting the 1-Gbit/s capacity requirement entails
extensive frequency reuse. Our solution is a 3-beamcluster model with about 70 beams [3]. A satellite
NTT Technical Review

Special Featureantenna with a gain of 43.5 dBi at EOL (end of life)
can provide 70 beams; this is equivalent to a 20-m
aperture. Making such a satellite based on conventional designs would yield a payload mass of morethan 800 kg. To reduce the system cost, we aim tohalve the payload mass [3], so the mass budget for thereflector is 130 kg, about half the weight of a conventional reflector [4]. An example of a satellite system configuration is shown in Fig. 1. A 20-m reflector is attached to a 1- or 1.5-ton-class satellite by aboom structure.

Ultralight large antenna reflector

Boom

3. Feasibility study of tendon-reinforced antennareflector
Fig. 1. System configuration.

3.1 Structural concept of an ultralight largeantenna reflector
Our structural design approach has two aspects.
The first is an extremely lightweight support structurein which the non-linearity of its structural behavior istaken into account. The other is a cable network structure that maintains the reflector’s shape even if the
support structures are severely deformed by in-orbit
thermal and/or vibration disturbances. Our proposal
is a geodesic cable network structure that is extended
and supported by a tendon-reinforced deployable
frame structure [5].
The concept of the resulting ultralight large antenna reflector is illustrated in Fig. 2. The key design
advance is that the accuracy of the reflector’s surface
is determined by a geodesic cable network structure;
the support structure simply tensions the geodesic
cable network. To stiffen the deployable frame structures, we use tendon cables to restrain the post-buckling displacement between the deployable frame
structures.
3.2 Feasibility study of structural concept
The feasibility of this structure was evaluated bydetailed analyses and tests conducted on a breadboard model. As shown in Fig. 3, we fabricated abreadboard model of the support structure; its diameter was 3.7 m. The support structure consists of six
deployable frame structures arranged around a stiff
post. The deployable frame structures were designed
to form a spherical shell that best fits the desired parabolic surface. Some of the nodes on the deployable
frame structures are connected by tendon cables.
Although the geodesic cable network structure andthe metallic mesh are not included in this model, theircompressive forces are represented by dummycables. Theoretical and measured results for bending
Vol. 5 No. 1 Jan. 2007

Geodesic cable
network structure +metallic mesh

Tendons

Deployable frame structure
Support structure

Fig. 2. Concept of our ultralight large antenna reflector.

stress are compared in Fig. 4.
The theoretical result matches the average of themeasured results, which deviate significantly due tomanufacturing tolerances and assembly errors.
Therefore, the characteristics of the proposed structures can be estimated by the analysis method
described herein. From our investigation, we reached
the following conclusions [6].
(1) The tendons effectively suppress post-buckling
deformation in the support structure. The use of
tendon cables increases the compression rigidity of the long ribs of the support structure byaround 10 times and their compression strengthby 4 times.
(2) Assuming that the thermal distortion of the sup71

Special Feature#1–6: frame structure id numbers
3

2

Frame
structure

A1

A 4

Tendoncable
5

63750 mm

port structure is 2 mm, the reflector structure
has sufficient margin (surface accuracy) against
disturbances while in orbit (confirmed by a sensitivity analysis for cable networks).
Therefore, the characteristics of the deployablereflector can be estimated by analysis, and this reflector can offer a lower weight.
3.3 Issues for detailed design
In order to advance the design status to the levelneeded for engineering and/or pre-flight modeling,
the following issues must be carefully considered.
(1) Confirmation of the detailed structural designof the support structure(2) Manufacturability of the geodesic cable network structure(3) Detailed design of mechanisms(4) System compatibilities
There are also other important issues that we must
consider to improve system reliability. These include
test and verification methods for deployment reliability, structural stiffness/strength, and surface accuracy.
These issues are not covered in this article.
4. Detailed design consideration andmanufacturability

Fig. 3. Breadboard model of reflector.

5

Bending stress (MPa)

0
–5
–10
–15
–20
–25
0

Theoretical
Frame structure 1
Frame structure 2
Frame structure 3
Frame structure 4
Frame structure 5
Frame structure 6
20

40

60

80

100

120

Drive cable tension (N)Fig. 4. Static load response (bending of the upper side)
versus cable tension. The red line shows theresult of theoretical analysis and the symbols
show measured data for individual frames.

72

4.1 Detailed design of deployable support
structure
As described above, the target mass of the antennareflector (20 m in diameter) is 130 kg, including theboom structure. While reducing the mass of theantenna reflector, we had to maintain a sufficientmargin of safety against applied compressive force.
To minimize the structural mass, we examined threedesign parameters: representative tube diameter, tube
thickness, and height of the frame structure.
When designing a structure of this type, we need totake into account the large deformation and structure
buckling expected. To deal with the large deformation, a co-rotational formulated finite element methodwith direct coordinate partitioning [7] was implemented on the analysis tool SPADE (simple partitioning algorithm based dynamics of finite element).
We enhanced the previous version of SPADE byadding a new computational method that can find abifurcation point and estimate the buckling mode: its
validity was confirmed by comparing the analyticalresult to the theoretical solution for a simple beam
structure. We used the new design tool to analyze theequilibrium shape and deployment motion of the proposed structure. The analysis model for a 20-m-diamNTT Technical Review

Special Feature

Fig. 5. Analysis model.

Hinge: aluminum, representative diameter: 18 mm
200
25Ultimate load
Limit load
Total mass

190
180
170
160

15

150
140

10

130
5

4.2 Geodesic cable network structure design
optimization considering manufacturability
The design parameters for the geodesic cable network structure are elasticity, initial length, andstrength of cable elements. We must determine theseparameters considering current manufacturing capabilities. For example, the elasticity of a cable element
can be reduced by reducing the cable diameter. However, this lowers cable strength.
Since the geodesic cable network structure determines the accuracy of the reflector, it must be manufactured using well-proven techniques. From thispoint of view, the most important issue is to decrease
the ratio of maximum to minimum cable tension. Theease of manufacturing the cable elements is restrictedby both the maximum and the minimum tension. The
maximum tension is limited by cable strength for agiven diameter and also by fastener strength (cable toterminal). Meanwhile, the minimum tension is determined by the achievable accuracy in cable tension.
Moreover, the tension ratio is large when the geodesic cable network structure consists of many cables.
Two design parameters were found to be effective at
reducing the tension ratio: the number of cables andthe depth of the edge catenary, as shown in Fig. 7. The
Vol. 5 No. 1 Jan. 2007

Total mass (kgf)20
Acceptable load (kgf)eter antenna reflector is shown in Fig. 5. Tendons aretreated as cables and each frame structure is composed of beam elements connected by hinge elements.
We evaluated two compressive force limits: 1) the
limit load, which is the limit indicated by the linear
stress response, and 2) the ultimate load, which is theload at which the stress in the most critical member
reaches a margin of safety of 0.5. We also calculated
the total mass of the reflector including the boom
based on the structural mass obtained using the analysis model. For simplicity, the compressive forces created by the geodesic cable network structure and themesh were represented by dummy cables. The mass
ratios of hinges, deployment mechanisms, and othernon-structural assemblies to the structural mass were
determined using previously developed models.
As one analytical result, Fig. 6 shows the effect oftube thickness on both acceptable load and total
mass. The limit load is not linear against wall thickness due to the load created by post-buckling displacement. Assuming that the maximum appliedcompressive force is 100 N, we should choose a representative tube diameter of 18 mm and thickness of
0.7 mm. In this case, we can reach the total mass of
149 kg with a margin of safety value of 0.5.

120
110

0
0.5

0.6

0.7

0.8

0.9

100
1.0

Tube wall thickness (mm)Fig. 6. Effect of tube thickness on acceptable load andtotal mass.

3 facets in radial direction

15 facets in radial direction

Edge catenary

Fig. 7. Effective parameters for tension ratio.

73Special Feature

5000

8000

4000
6000
3000
4000
2000
Number ofcables

2000

0

2

4

6

8

10

12

14

16

1000
0
18

Number of facets in radial direction

Fig. 8. Tension ratio versus the number of facets.

number of cables is represented by the number offacets along the reflector’s radius, and the catenary
depth is represented by the ratio of the peak of thecatenary edge to the edge length.
As shown in Fig. 8, increasing the number of facets
rapidly increases the tension ratio. On the other hand,the number of facets strongly affects the surface random error from the ideal parabolic surface. The allotted random error for the facet approximation shouldbe less than 0.5 mm (rms), so the number of facets
should be more than 10.
The effect of catenary depth on the tension ratio isshown in Fig. 9. The tension ratio decreases rapidly
as the ratio of the catenary peak to the edge length
increases. The catenary also affects the peak electrical gain of the antenna reflector, so it should be limited to around 10%. The tension ratio is expected todecrease to a value of several hundred when the catenary ratio is 10%. Considering that the maximum
cable tension is estimated to be 100 N, the minimum
cable tension will be more than 0.1 N, which eases
manufacturing concerns. In addition, decreasing the
maximum cable tension reduces the mass of the
deployment support structure.
These results show that with 10 facets the catenary
ratio is around 8% to 10% and the cable tension is
acceptable.
4.3 Detailed mechanism design
Since the composition of the mechanism is customized for each structure, it is difficult to decide themass of mechanisms, such as deployment drive
mechanisms, control mechanisms, and hold/releasemechanisms, by estimation based on the analytical
74

7000
Maximum/minimum tension ratio

6000

Number of cables

Maximum/minimum tension ratio

10000

6000
15 facets in radial direction

5000
4000
3000
2000

10 facets in radial direction
1000
1

2

3

4

5

6

7

8

9

Peak of edge catenary –: edge length (%)

Fig. 9. Tension ratio versus catenary.

model. As described previously, the total mass of ourreflector should be 149 kg; however, the accuracy of
estimating the mass budget for mechanisms (nonstructural mass) is problematic because these masses
are assumed to be proportional to the structural massusing the relationships developed for traditional
designs. Therefore, detailed design of the mechanisms for the real scale is required to clarify the massand the potential problems with installation on asatellite. We examined these mechanisms for a real
20-m-scale reflector in detail. Structural and mechanism design drawings were created based on thedesign heritage of Engineering Test Satellite VIII.
The aperture and catenary (top view) are shown in
Fig. 10. The structural design parameters, such as
tube diameter and thickness, were taken from theresults in section 4.1.
A side view of the structure in the fully deployedconfiguration is shown in Fig. 11, and the basic cellstructure is shown in Fig. 12. Frame structures arecomposed of several basic cell structures, each consisting of several beam members connected to eachother via revolute hinges to permit stowage anddeployment. They form two quadrangular frames. To
each frame, we added diagonal members that can befolded at an intermediate position. The main driving
force is provided by coil-spring-driven four-bar linkage arms attached to the central axis. The linkage arm
mechanism is set at a geometrically singular position
when the basic cell structure is completely stowed.
Therefore, we installed an ancillary coil-spring at theconnection hinge between the central lateral member
and the lower radial member. Some details of thedrive linkage arms and the ancillary coil-spring are
NTT Technical Review

Special Featureshown in Fig. 13. In addition, to avoid tendon cableentanglement and to enhance the synchronization of
the deployment behavior, the tendon cables arewound on drums and released passively as the reflector deploys. The drums are installed at the connection
points of tendon cables.

12,702
φ20,000

1000

11,000

Unit: mm

4.4 System compatibility
To clarify the problem of achieving the target mass
budget, we estimated the total mass of our reflector
structure from the above-mentioned design drawings.
In addition, we also considered antenna dimensions
in the stowed configuration to clarify the installation
feasibility for launch vehicles.
4.4.1 Mass budget of antenna reflector
Details of the support structure masses are shown in
Table 1. The masses of the holding structure, driving
and control mechanism, ancillary spring, and tendon

Fig. 10. Aperture and edge catenary.
Lower radial
members

Central lateral
member

24,48043

Basic cellstructure1

11,643476

26,4

Hub structure
3391

Holding structure

Unit: mmFig. 11. Deployed configuration of rib structure.
Ancillary springs

Drive linkage

Fig. 13. Details of mechanism design.

Table 1. Detailed mass budget in support structure.
3912

Driven four-bar linkage arms

1546

4540
Unit: mmFig. 12. Basic cell structure.

Vol. 5 No. 1 Jan. 2007

Analysis

Design drawing

Structural member

38

37

Deployment mechanism

118

Holding structure

4

10

Drive/control mechanism

11

39

Ancillary spring

0

14

Tendon structure

0

14

Total

64

122
Unit: kg

75

Special Feature

5. Conclusion
To make an ultralight large antenna reflector, wehave proposed a new structural concept and confirmed its basic feasibility. Detailed structural andmechanism designs were carefully considered, as
well as manufacturability and system compatibility.
The following conclusions were reached.
(1) Assuming that the maximum applied compressive force is 100 N, our design has a representative tube diameter of 18 mm and thickness of
0.7 mm. In this case, we can hold the total mass
down to 149 kg with a margin-of-safety valueof 0.5.
(2) The ratio of maximum to minimum cable tension in the geodesic cable network structure is
expected to decrease to several hundred when
the catenary depth is 10%. Considering that the
maximum cable tension is estimated to be 100
N, the minimum cable tension will be more
76

Table 2. Mass of antenna reflector.
AnalysisPrimary

Present

Designdrawing

Cable-mesh reflector

20

(20)

(20)

Support structure

66

64

122

Holding/release structure

34

33

37

Boom

32

(32)

(32)

Total

152

149

211

Component

Unit: kg( ) not designed at this time

B–B

A–A
B

A
1576

structure (including drums) exceed the estimated values used in the analysis. The main reason for this discrepancy is that the design drawings of the mechanisms were based on a two-dimensional deployment
structure with the conventional mechanism design
methodology.
The mass budget of the antenna reflector in comparison with the results of the analytical estimation
are shown in Table 2. This table shows that the massestimated from the design drawings of the deployment support structure is twice that yielded by the
analytical estimation. As mentioned above, this difference is caused by the non-structural members of
the support structure. Consequently, the first detailed
design trial for these mechanisms shows that a new
design methodology is needed to reduce the mass ofthe deployment drive and control mechanisms for
one-dimensional deployable structures.
4.4.2 Stowed configuration
If the target stowed size is to be compatible with thefairing of Sea Launch (diameter: 3.75 m) or Speltraof ARIANE5 (diameter: 4.57 m, height: 5 m), thenthe maximum stowed size should be a diameter of 1.6
m and height of 3.5 m. The stowed dimensions
obtained from the detailed design are a maximum
diameter of 1.6 m and height of about 4 m, as shownin Fig. 14. Therefore, to meet the target height of 3.5m, the aperture must be reduced to 19 m, which stillyields acceptable electrical performance. In addition
to the mass budget, we need to refine the dimensions
to achieve a sufficient margin.

B
A
1603
Tendon cable pulley3997

Holding/releasestructure
Unit: mmFig. 14. Stowed configuration.

than 0.1 N, which simplifies manufacture.
(3) Mechanism design drawings were generated
based on the conventional mechanism design
methodology. The first detailed design trial forthe reflector mechanisms clarified that a new
design methodology is needed to reduce themass of the deployment drive and control
mechanisms.
To achieve our goals, we will continue to study theremaining issues associated with the mechanisms andalso refine the overall dimensions considering system
requirements.
References
[1]

[2]

[3]

[4]

M. W. Thomson, “ASTROMESH Deployable Reflectors for Ku and
Ka Band Commercial Satellites,” Proc. ICSSC, AIAA-2002-2032,
2002.
T. Smith, B. Lee, D. Semler, and D. Chae, “A Large S-band Antenna
for a Mobile Satellite,” Space 2004 Conference and Exposition, San
Diego, CA, Sep. 28-30, AIAA-2004-6120, 2004.
M. Ueba, K. Ohata, J. Mitsugi, and M. Umehira, “Broadband andscalable mobile satellite communication system for future access networks,” Proc. of 22nd ICSSC, Monterey, AIAA-2004-3154, 2004.
Y. Suzuki, A. Meguro, K. Kobayashi, and M. Ueba, “Multibeam

NTT Technical Review

Special Feature

[5]

[6]

[7]

Phased Array Feed System Using Beam Group Concept ,” NTT Technical Review, Vol. 5, No. 1, pp. 61-69, 2007.
S. Harada, A. Meguro, and M. Watanabe, “New Tendon Reinforced
Reflector for Large-Scale and Ultra-Lightweight Antenna onboard
the Satellite,” 45th Structures Structural Dynamics and Materials
Conference, Palm Springs, AIAA-2004, 2004.
A. Meguro, S. Harada, and M. Ueba, “A Feasibility Study of an UltraLight Large Antenna Reflector for Future Mobile Communications
Satellites,” 56th International Astronautical Congress, Fukuoka, IAF05-C2.1.B. 02, 2005.
J. Mitsugi, Direct Coordinate “Partitioning for Multibody Dynamics
Based on Finite Element Method,” 36th Structures Structural Dynamics and Materials Conference, AIAA-95-1442-CP, 1995.

Satoshi Harada
Senior Research Engineer, Satellite Communication Systems Group, Wireless Access Systems
Project, NTT Access Network Service Systems
Laboratories.
He received the B.E. and M.E. degrees inmechanical engineering from Keio University,
Tokyo, in 1990 and 1992, respectively. Sincejoining NTT Wireless System Laboratories in
1992, he has been engaged in research on large
deployable antenna reflectors. He is a member ofthe American Institute of Aeronautics and Astronautics (AIAA).

Akira Meguro
Associate Senior Engineer, Engineering Test
Satellite VIII Project, Japan Aerospace Exploration Agency (JAXA), Office of Space Applications.
He received the B.E. and M.E. degrees inmechanical engineering from Keio University,
Tokyo, and the Ph.D. degree in aerospace engineering from the University of Tokyo, Tokyo, in
1983, 1985, and 2004, respectively. He joined
NTT in 1985. His main field is R&D of spacecraft structures. In particular, he has been studying large deployable antenna reflectors on board
communication satellites. He has worked for several satellite projects such as ETS-VI, VSOP, NStar c, and ETS-VIII. He moved to Japan Aerospace Exploration Agency in 2006.

Masazumi Ueba
Senior Research Engineer, Supervisor, Group
Leader, Satellite Communication Systems
Group, Wireless Access Systems Project, NTT
Access Network Service Systems Laboratories.
He received the B.E. and M.S. degrees in aeronautical engineering, and the Dr.Eng. degree forwork on the design methodology of highly accurate antenna pointing system from the Universityof Tokyo, Tokyo, in 1982, 1984, and 1996,
respectively. He joined the Yokosuka ElectricalCommunication Laboratories of Nippon Telegraph and Telephone Public Corporation (nowNTT) in 1984. He has been engaged in researchon the dynamics of antenna pointing control systems of satellites and shape control systems forlarge antenna reflectors. He is currently researching technologies for next-generation mobile
satellite communication systems. He is a memberof the Institute of Electronics, Information andCommunication Enginees of Japan, the Japan
Society for Aeronautical and Space Sciences,and AIAA.

Vol. 5 No. 1 Jan. 200777