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Fan rib type deployable mesh antenna for satellite use
Acta Astronauttca Vol. 17, No. 5, pp. 561-566, 1988 Printed in Great Britain
FAN
RIB
TYPE FOR
0094-5765/88 $3.00+ 0.00 Pergamon Press pie
DEPLOYABLE
MESH
SATELLITE
ANTENNA
USEr
T. ITANAMI, M. MINOMO a n d I. OHTOMO NTT Electrical Communications Laboratories, 1-2356, Take, Yokosuka-shi, Kanagawa, Japan
(Received 6 January 1987; revised version received 23 October 1987) A~traet--This paper presents a design for satellite-borne 3.5 m deployable mesh reflector for the Japanese maritime satellite communication system. The features of this antenna are compactness, lightness and high deployment reliability. The measured characteristics for the engineering model are also given.
1. INTRODUCTION
The Japanese maritime satellite communication system[l] has been actively studied for the past several years. Major features of the proposed system are as follows: (1) A multibeam satellite communication system used to achieve small size, low cost ship terminals. (2) S band (2.6/2.5 GHz) used for the link between ship terminals and the satellite. (3) The radiation pattern of the antenna is a multiple beam superimposition of circular beams which cover an area within 200 nautical miles around the Japanese main island (see Fig. 1). This paper presents a design for a satellite-borne S-band fan rib type deployable mesh antenna for this system. Measured characteristics for the engineering model are also given. 2. SELECTION OF REFLECTOR CONFIGURATION Some of the most important specifications for the S-band antenna are as follows: Spacecraft:
Pay load area: Stiffness: Gain in service area: Surface roughness:
ployable satellite antenna into the rocket fairing. However, it is difficult to attain a compact arrangement using a single reflector system since this would require arrangement of the reflector and feeds corresponding to a very long focal length of more than 5.8 m to assure good electrical performances. With a dual reflector system, a compact arrangement can easily be achieved, since a long equivalent focal length system is made possible by a main reflector with a short focal length, a small subreflector near the main reflector focus and feed horns arranged between the reflectors. The offset Cassegrain antenna, one of the dual reflector systems, has been selected for the object of this design. Several configurations for deployable mesh reflectors have been proposed, and some of these have been developed [2-6]. In view of the required reflector diameter, compactness, deployment reliance, lightness and ease of fabrication, a fan rib type deployable reflector with the simplest mechanical configuration and the least number of movable joints, has been selected for further detailed design.
a 550 1000 kg class 3 axis
stabilized bus in. dia 2.18 m height 2.8 m > 35 Hz axial 30 Hz lateral 31 dB 2 mm rms ( -/50)
o
Meosured
- 4 dB
O
The antenna configuration has to be determined so as to fulfil the above-mentioned requirements. As discussed below, a reflector with an aperature diameter larger than 3.5 m and a focal length of more than 5.8 m is necessary to attain the required gain and beam pattern shown in Fig. 1. Compact geometrical arrangement of antenna components, such as the reflector and feeds, in the deployed configuration is essential to place the de-
o~ o O >
I.U -1
-2 -3 -2
tBased on paper IAF-86-28 presented at the 37th Congress of the International Astronautical Federation, Innsbruck, Austria, 4-11 October 1986. 561
-1
0
1
Azimuth ( d e g )
Fig. 1. Antenna radiation pattern,
2
562
T. ITANAIdlet al. 3. ELECTRICAL DESIGN ----D
In advance of the detailed design for the offset Cassegrain antenna, a basic design using the equivalent parabola technique has been carried out. To obtain the beam pattern shown in Fig. 1, the 3 dB beam width and the beam separation angle are selected to 2 and 1.8 ° respectively. Variations of beam edge gain and beam separation angle with focal length F, plotted for aperture diameter D and feed horn size d (i.e. length between feed horn centres) as parameters, are shown in Fig. 2. These characteristics were calculated for the hexagonal horn feeds to obtain a smaller beam separation angle and higher beam edge gain. Figure 2 shows that there is an optimal focal length to obtain the highest beam edge gain for each D and d pair. It also shows that antenna with an aperture diameter larger than 3.5 m and a focal length longer than 5.8 m is necessary to attain the required beam edge gain and beam separation angle. A side view of launch and on-orbit configuration of the antenna is shown in Fig. 3. Antenna diameter is limited to less than 3.5 m for the payload area. The beam edge gain increases with increase of the diameter as shown in Fig. 2. Thus the main reflector diameter d is determined to be 3.5 m. The peak gain increases with the increase of the feed horn diameter because spill over from subreflector decreases. However, it decreases with the increase of feed horn diameter because of the blocking loss caused by feed horns. Taking these things into account, the diameter of the feed horns d is determined to be 195 mm. The equivalent focal length F of the offset Cassegrain antenna is determined to be 5.8 m, obtaining the highest beam edge gain for the determined D and d pair. The parameters of the equivalent parabola have been decided, However, there are many different Cassegrain antennas which satisfy the parameters of equivalent parabola with D = 3.5 m and F = 5.8 m. The main parameters of an offset Cassegrain antenna are the main reflector focal length, f~; subreflector focal length, f~; subreflector eccentricity, e; and subreflector angular aperture. Taking mechanical vibration characteristics into consideration, fro, f~, e are determined to be 2.5 m, 450 mm and 2.5, respectively. The subreflector angular aperture is determined through a current distribution method (CDM), taking the effect of finite subreflector aperture into account. The subreflector angular aperture determined through CDM is 48 ° and is about 40% larger than the aperture determined through geometrical optics, which does not take the finite aperture edge into account. The peak gain of each beam is greater than 36 dB and the cross over levels between adjacent beams are 4 dB below the peak gain. Gain degradation is primarily due to surface roughness, reflection loss of the mesh and ohmic loss at the feed circuit. The estimated
: 3 . 6 m, d : 200 m D = 3 . 6 m, d : 180 ,, -----D : 3 . 4 m, d = 200 m
32
. . . . . D : 3.4 m, d = 180 m
30
5
g
Focal
length
'
-2.2
7
( m )
:
7<,
=°°
8 1.8 la 1.4
4
I
I
5
g
Focal
length
( m )
Fig. 2. Focal length dependence of beam edge gain and beam separation angle.
gain degradation if 0.9 dB. Thus, the beam edge gain of more than 31 dB is obtained as a design result. The main electrical design values are shown in Table 1. 4. STRUCTURAL DESIGN
The main reflector is composed of 9 ribs of different lengths with spring-type deployment mechanism for each rib, a mesh reflecting surface in front of the ribs, quartz codes in the mesh, tension members behind the ribs and adjustors which connect the quartz codes and tension members to maintain the paraboloid shape of the mesh surface (Fig. 4).
pay
//
l
.~,,
,,,~> re,Leo,or ~-.<,.--t-'fixlnll bar
center rib /=
Load area
-
/ /J
~1
/
t=''\l
.~r,~, 3.5m
Fig. 3. Side view of stowed and on-orbit configuration.
Fan rib type deployable antenna
563
Table 1. Design and measured characteristics of deployable antenna No. of beams Aperture diameter of main reflector (D) Focal length of main reflector (fro) Focal length of subreflector (f,) Subreflector eccentricity (e) Angular aperture of subrefiector Antenna pointing accuracy
5 3.5m 2.5m 450 mm 2.5 48° 0.Y' Designed
Beam-edge gain (dB) Antenna weight (kg) Surface roughness of main reflector (mm rms) Eigen frequencies of first mode in stowed configuration
Axial Lateral
(Hz) (Hz)
31 21 2 > 35 30
Measured 31 20 1.7 > 40 27
Fig. 4. Main reflector configuration.
A detailed configuration study based on the electrical design of the offset Cassegrain antenna led to the choice of an ellipse with 3.4 m minor axis and 3.6m major axis for the main reflector aperture
diameter as an accommodation to the limited payload area. Major mechanical requirements for determining the configuration are the surface roughness of the
(a)
(b) Tower
\
SubrefLAnlor
Rib
i
Fig. 5. Fundamental vibration mode in stowed configuration. (a) Side view; (b) front view. A.A. I 7/5--.-H
564
T. ITANAMIet al.
deployed reflector and the stiffness of the rib in its stowed configuration. A 1/5 scale model of the mesh reflector has been made to examine the properties of the mesh surface. Examination of the reflector clarifies that the surface roughness within 2 mm rms is feasible by supporting the mesh surface with ribs and/or quartz cords in a radial direction at intervals of 3-3.5. Therefore, the designed 3.5 m mesh reflector surface is supported with 3 quartz cords between ribs in a radial direction at intervals of 3.5 ~. Ribs with cross-sections of larger diameter and thinner skin are employed to obtain a reflector with lighter weight and more stiffness. The ribs are usually
fixed at the top with fixing bars, and at the bottom with deployment mechanisms in the stowed configuration. To raise the lowest natural frequency, the attachment point of the fixing bars is changed to a point one-third of the full length from the top. This change provides an increase in the lowest natural frequency with a thinner skin. An eigen value analysis using NASTRAN was carried out for the stowed configuration of the reflector. The results of the analysis are shown in Table 1. The fundamental vibration mode as shown in Fig. 5 is a bending in the lateral direction. The antenna gain loss caused by the fixing bar blockings is sufficiently small ( < 0.1 dB).
Fig. 6. Manufactured mesh deployable antenna. (a) Stowed; (b) deployed.
Fan rib type deployable antenna Thus, a main reflector with a lowest natural frequency of 30 Hz in stowed configurations is designed. The designed cross-section of the rib has a 50 mm average dia and I mm thickness. The total weight of the designed antenna is 21 kg, including the weight of the subreflector and the feeds. 5. CHARACTERISTICS OF THE MANUFACTURED M E S H ANTENNA
A engineering model of the 3.5 m dia fan rib type deployable mesh antenna has been manufactured on the basis of the electrical and mechanical design mentioned above. The manufactured antenna is shown in Fig. 6 with a 1.3 m solid reflector antenna for trunk transmission and feeder link. 5.1. Electrical characteristics
The measured radiation pattern of the antenna is shown in Fig. 1 together with the designed pattern.
E
2
l
o
=
The measured pattern has an elliptical contour because of elliptical shape of the main reflector and off focus feed. The beam edge gain is 31 dB and agrees with designed value. The required beam separation angle of 2 ° is slightly larger than the designed value. The examples of measured surface roughness, i.e. a deviation from an ideal paraboloid, is shown in Fig. 7. Measurement has been made for about 1000 points all over the mesh surface by a laser measurement system. The measured surface roughness of 1.7 mm rms is sufficiently small. Measured sidelobe characteristics are shown in Fig. 8. The main reflector structure can easily cause periodical distortion. The sidelobe characteristics, with periodical distortion of 1 m in pitch and 4 mm in height, are indicated by the dotted line in Fig. 8. In comparison of these characteristics, it is confirmed that there are no sidelobes caused by periodical distortion.
4
[
5
J Rib number
8
565
6
7
8
]
J
I
• o
/
4
I
I
2
3
Position
in r a d i a l direction ( m )
-4
Fig. 7. Measured surface roughness.
Periodic ~, Pitch '~\\/Height
•o - 2 0
distortion Im 4mrn p - p
~" o -40
#= - 60 - 180
I
I
I 0
Azimuth (deg)
Fig. 8. Sidelobe characteristics of manufactured antenna.
t80
566
T. ITANAMIet al. 10
Table 2. Eigen frequencies and vibration modes in stowed configuration (analysis) Znput Level : 0 . 2 G Monitored
Point Direction
Central
Rib Tip
Condition Mode No. 1
Y
2
Without fixture
With fixture
27.9 Hz Y, Bending 34.6 Hz X, Rib local
26.4 Hz Y, Bending 29.5 Hz X, Bending
o Ip
The measured main reflector mass per unit area was 1.5 kg/m 2, including 9 deployment mechanisms and a solid shell part. 0.1
i
I
I
10
I 50
I
CONCLUSION
I I il 100
Frequency(Hz)
Fig. 9. Response curve of vibration test.
5.2. Structural characteristics
The antenna deployment test was carried out in order to test the function of deployment mechanisms and the behavior of the ribs and cables during deployment. The accuracy of the deployment angle was also evaluated in the test. In order to compensate for the gravity effect, gravity compensation springs were adopted in all deployment mechanisms during the deployment test. The deployment angle errors obtained were <0.01 °, which were good enough to maintain the antenna pointing accuracy required by the electrical performance. Figure 9 shows one of the response curves of the sinusoidal vibration test in the stowed configuration. The first resonance occurred at 25 Hz. The eigen frequencies obtained in the vibration tests were reduced by about 10% due to the flexibility of the test fixture. This effect was estimated analytically using two models, i.e. one with the fixture and the other without. These results are shown in Table 2. As for the fundamental eigen frequency, the difference between those two conditions was about 2 Hz. Then, it is concluded that the fundamental eigen frequency of the antenna without the fixture effect will be 27 Hz. The design goal of 30 Hz can be achieved easily with a slight design change to improve rib stiffness and the clamping condition of fixing bars. Since the vibration testing of the deployed configuration was difficult to conduct for the reflector, model tests on individual ribs were carried out. The measured fundamental frequencies were over 5 Hz for all ribs, which satisfied the requirement of more than 2 Hz.
Electrical and mechanical designs have been made for the deployable mesh antenna mounted on the 3 axis stabilized bus and stowed in rocket fairings with a 2 m i.d. Electrical, structural and thermal examinations have been made for this antenna. The electrical and structural designs and test results of the manufactured antenna are described here. It is verified from these results that the characteristics of the manufactured antenna well agree with the designed values. The system requirements can be achieved easily with a small design improvement. The thermal design and test have been made simultaneously and it is confirmed that this antenna has a good thermal performance. These results will be reported with the reliability test results for the deployment mechanisms. Acknowledgement--The authors would like to acknowledge
Dr Heiichi Yamamoto and Dr Tetsuo Yasaka for their continued guidance and encouragement. REFERENCES
1. K. Miyauchi, Communication equipment technology of Japanese domestic communication satellites. AIAA lOth Communications Satellite Conf., AIAA 84-0681 (1984). 2. R. V. Powell, A future for large space antennas. AIAA 7th Communications Satellite Conf., AIAA 78-0588 (1978). 3. R. A. Russell and T. G. Cambell, A technology development program for large space antennas. 31th IAF Congress, IAF-80A-33 (1980). 4. J. A. Fager and R. Garriott, Large-aperture extendabletruss microwave antenna. IEEE Trans. AP-17, 452-458 (1969). 5. B. C. Tankersley and H. E. Bartlett, Tracking and datarelay satellite single access deployable antenna. National
Telecommunications
Conference
Records
NTC-77, 19-4 (1977). 6. W. Schafer, H. Harbig, A. Roederer and K. Pontoppidan, Unfurlable offset antenna design for L and C-band application. AIAA 9th Communications Satellite Conf., AIAA 82-0443 (1982).
FAN
RIB
TYPE FOR
0094-5765/88 $3.00+ 0.00 Pergamon Press pie
DEPLOYABLE
MESH
SATELLITE
ANTENNA
USEr
T. ITANAMI, M. MINOMO a n d I. OHTOMO NTT Electrical Communications Laboratories, 1-2356, Take, Yokosuka-shi, Kanagawa, Japan
(Received 6 January 1987; revised version received 23 October 1987) A~traet--This paper presents a design for satellite-borne 3.5 m deployable mesh reflector for the Japanese maritime satellite communication system. The features of this antenna are compactness, lightness and high deployment reliability. The measured characteristics for the engineering model are also given.
1. INTRODUCTION
The Japanese maritime satellite communication system[l] has been actively studied for the past several years. Major features of the proposed system are as follows: (1) A multibeam satellite communication system used to achieve small size, low cost ship terminals. (2) S band (2.6/2.5 GHz) used for the link between ship terminals and the satellite. (3) The radiation pattern of the antenna is a multiple beam superimposition of circular beams which cover an area within 200 nautical miles around the Japanese main island (see Fig. 1). This paper presents a design for a satellite-borne S-band fan rib type deployable mesh antenna for this system. Measured characteristics for the engineering model are also given. 2. SELECTION OF REFLECTOR CONFIGURATION Some of the most important specifications for the S-band antenna are as follows: Spacecraft:
Pay load area: Stiffness: Gain in service area: Surface roughness:
ployable satellite antenna into the rocket fairing. However, it is difficult to attain a compact arrangement using a single reflector system since this would require arrangement of the reflector and feeds corresponding to a very long focal length of more than 5.8 m to assure good electrical performances. With a dual reflector system, a compact arrangement can easily be achieved, since a long equivalent focal length system is made possible by a main reflector with a short focal length, a small subreflector near the main reflector focus and feed horns arranged between the reflectors. The offset Cassegrain antenna, one of the dual reflector systems, has been selected for the object of this design. Several configurations for deployable mesh reflectors have been proposed, and some of these have been developed [2-6]. In view of the required reflector diameter, compactness, deployment reliance, lightness and ease of fabrication, a fan rib type deployable reflector with the simplest mechanical configuration and the least number of movable joints, has been selected for further detailed design.
a 550 1000 kg class 3 axis
stabilized bus in. dia 2.18 m height 2.8 m > 35 Hz axial 30 Hz lateral 31 dB 2 mm rms ( -/50)
o
Meosured
- 4 dB
O
The antenna configuration has to be determined so as to fulfil the above-mentioned requirements. As discussed below, a reflector with an aperature diameter larger than 3.5 m and a focal length of more than 5.8 m is necessary to attain the required gain and beam pattern shown in Fig. 1. Compact geometrical arrangement of antenna components, such as the reflector and feeds, in the deployed configuration is essential to place the de-
o~ o O >
I.U -1
-2 -3 -2
tBased on paper IAF-86-28 presented at the 37th Congress of the International Astronautical Federation, Innsbruck, Austria, 4-11 October 1986. 561
-1
0
1
Azimuth ( d e g )
Fig. 1. Antenna radiation pattern,
2
562
T. ITANAIdlet al. 3. ELECTRICAL DESIGN ----D
In advance of the detailed design for the offset Cassegrain antenna, a basic design using the equivalent parabola technique has been carried out. To obtain the beam pattern shown in Fig. 1, the 3 dB beam width and the beam separation angle are selected to 2 and 1.8 ° respectively. Variations of beam edge gain and beam separation angle with focal length F, plotted for aperture diameter D and feed horn size d (i.e. length between feed horn centres) as parameters, are shown in Fig. 2. These characteristics were calculated for the hexagonal horn feeds to obtain a smaller beam separation angle and higher beam edge gain. Figure 2 shows that there is an optimal focal length to obtain the highest beam edge gain for each D and d pair. It also shows that antenna with an aperture diameter larger than 3.5 m and a focal length longer than 5.8 m is necessary to attain the required beam edge gain and beam separation angle. A side view of launch and on-orbit configuration of the antenna is shown in Fig. 3. Antenna diameter is limited to less than 3.5 m for the payload area. The beam edge gain increases with increase of the diameter as shown in Fig. 2. Thus the main reflector diameter d is determined to be 3.5 m. The peak gain increases with the increase of the feed horn diameter because spill over from subreflector decreases. However, it decreases with the increase of feed horn diameter because of the blocking loss caused by feed horns. Taking these things into account, the diameter of the feed horns d is determined to be 195 mm. The equivalent focal length F of the offset Cassegrain antenna is determined to be 5.8 m, obtaining the highest beam edge gain for the determined D and d pair. The parameters of the equivalent parabola have been decided, However, there are many different Cassegrain antennas which satisfy the parameters of equivalent parabola with D = 3.5 m and F = 5.8 m. The main parameters of an offset Cassegrain antenna are the main reflector focal length, f~; subreflector focal length, f~; subreflector eccentricity, e; and subreflector angular aperture. Taking mechanical vibration characteristics into consideration, fro, f~, e are determined to be 2.5 m, 450 mm and 2.5, respectively. The subreflector angular aperture is determined through a current distribution method (CDM), taking the effect of finite subreflector aperture into account. The subreflector angular aperture determined through CDM is 48 ° and is about 40% larger than the aperture determined through geometrical optics, which does not take the finite aperture edge into account. The peak gain of each beam is greater than 36 dB and the cross over levels between adjacent beams are 4 dB below the peak gain. Gain degradation is primarily due to surface roughness, reflection loss of the mesh and ohmic loss at the feed circuit. The estimated
: 3 . 6 m, d : 200 m D = 3 . 6 m, d : 180 ,, -----D : 3 . 4 m, d = 200 m
32
. . . . . D : 3.4 m, d = 180 m
30
5
g
Focal
length
'
-2.2
7
( m )
:
7<,
=°°
8 1.8 la 1.4
4
I
I
5
g
Focal
length
( m )
Fig. 2. Focal length dependence of beam edge gain and beam separation angle.
gain degradation if 0.9 dB. Thus, the beam edge gain of more than 31 dB is obtained as a design result. The main electrical design values are shown in Table 1. 4. STRUCTURAL DESIGN
The main reflector is composed of 9 ribs of different lengths with spring-type deployment mechanism for each rib, a mesh reflecting surface in front of the ribs, quartz codes in the mesh, tension members behind the ribs and adjustors which connect the quartz codes and tension members to maintain the paraboloid shape of the mesh surface (Fig. 4).
pay
//
l
.~,,
,,,~> re,Leo,or ~-.<,.--t-'fixlnll bar
center rib /=
Load area
-
/ /J
~1
/
t=''\l
.~r,~, 3.5m
Fig. 3. Side view of stowed and on-orbit configuration.
Fan rib type deployable antenna
563
Table 1. Design and measured characteristics of deployable antenna No. of beams Aperture diameter of main reflector (D) Focal length of main reflector (fro) Focal length of subreflector (f,) Subreflector eccentricity (e) Angular aperture of subrefiector Antenna pointing accuracy
5 3.5m 2.5m 450 mm 2.5 48° 0.Y' Designed
Beam-edge gain (dB) Antenna weight (kg) Surface roughness of main reflector (mm rms) Eigen frequencies of first mode in stowed configuration
Axial Lateral
(Hz) (Hz)
31 21 2 > 35 30
Measured 31 20 1.7 > 40 27
Fig. 4. Main reflector configuration.
A detailed configuration study based on the electrical design of the offset Cassegrain antenna led to the choice of an ellipse with 3.4 m minor axis and 3.6m major axis for the main reflector aperture
diameter as an accommodation to the limited payload area. Major mechanical requirements for determining the configuration are the surface roughness of the
(a)
(b) Tower
\
SubrefLAnlor
Rib
i
Fig. 5. Fundamental vibration mode in stowed configuration. (a) Side view; (b) front view. A.A. I 7/5--.-H
564
T. ITANAMIet al.
deployed reflector and the stiffness of the rib in its stowed configuration. A 1/5 scale model of the mesh reflector has been made to examine the properties of the mesh surface. Examination of the reflector clarifies that the surface roughness within 2 mm rms is feasible by supporting the mesh surface with ribs and/or quartz cords in a radial direction at intervals of 3-3.5. Therefore, the designed 3.5 m mesh reflector surface is supported with 3 quartz cords between ribs in a radial direction at intervals of 3.5 ~. Ribs with cross-sections of larger diameter and thinner skin are employed to obtain a reflector with lighter weight and more stiffness. The ribs are usually
fixed at the top with fixing bars, and at the bottom with deployment mechanisms in the stowed configuration. To raise the lowest natural frequency, the attachment point of the fixing bars is changed to a point one-third of the full length from the top. This change provides an increase in the lowest natural frequency with a thinner skin. An eigen value analysis using NASTRAN was carried out for the stowed configuration of the reflector. The results of the analysis are shown in Table 1. The fundamental vibration mode as shown in Fig. 5 is a bending in the lateral direction. The antenna gain loss caused by the fixing bar blockings is sufficiently small ( < 0.1 dB).
Fig. 6. Manufactured mesh deployable antenna. (a) Stowed; (b) deployed.
Fan rib type deployable antenna Thus, a main reflector with a lowest natural frequency of 30 Hz in stowed configurations is designed. The designed cross-section of the rib has a 50 mm average dia and I mm thickness. The total weight of the designed antenna is 21 kg, including the weight of the subreflector and the feeds. 5. CHARACTERISTICS OF THE MANUFACTURED M E S H ANTENNA
A engineering model of the 3.5 m dia fan rib type deployable mesh antenna has been manufactured on the basis of the electrical and mechanical design mentioned above. The manufactured antenna is shown in Fig. 6 with a 1.3 m solid reflector antenna for trunk transmission and feeder link. 5.1. Electrical characteristics
The measured radiation pattern of the antenna is shown in Fig. 1 together with the designed pattern.
E
2
l
o
=
The measured pattern has an elliptical contour because of elliptical shape of the main reflector and off focus feed. The beam edge gain is 31 dB and agrees with designed value. The required beam separation angle of 2 ° is slightly larger than the designed value. The examples of measured surface roughness, i.e. a deviation from an ideal paraboloid, is shown in Fig. 7. Measurement has been made for about 1000 points all over the mesh surface by a laser measurement system. The measured surface roughness of 1.7 mm rms is sufficiently small. Measured sidelobe characteristics are shown in Fig. 8. The main reflector structure can easily cause periodical distortion. The sidelobe characteristics, with periodical distortion of 1 m in pitch and 4 mm in height, are indicated by the dotted line in Fig. 8. In comparison of these characteristics, it is confirmed that there are no sidelobes caused by periodical distortion.
4
[
5
J Rib number
8
565
6
7
8
]
J
I
• o
/
4
I
I
2
3
Position
in r a d i a l direction ( m )
-4
Fig. 7. Measured surface roughness.
Periodic ~, Pitch '~\\/Height
•o - 2 0
distortion Im 4mrn p - p
~" o -40
#= - 60 - 180
I
I
I 0
Azimuth (deg)
Fig. 8. Sidelobe characteristics of manufactured antenna.
t80
566
T. ITANAMIet al. 10
Table 2. Eigen frequencies and vibration modes in stowed configuration (analysis) Znput Level : 0 . 2 G Monitored
Point Direction
Central
Rib Tip
Condition Mode No. 1
Y
2
Without fixture
With fixture
27.9 Hz Y, Bending 34.6 Hz X, Rib local
26.4 Hz Y, Bending 29.5 Hz X, Bending
o Ip
The measured main reflector mass per unit area was 1.5 kg/m 2, including 9 deployment mechanisms and a solid shell part. 0.1
i
I
I
10
I 50
I
CONCLUSION
I I il 100
Frequency(Hz)
Fig. 9. Response curve of vibration test.
5.2. Structural characteristics
The antenna deployment test was carried out in order to test the function of deployment mechanisms and the behavior of the ribs and cables during deployment. The accuracy of the deployment angle was also evaluated in the test. In order to compensate for the gravity effect, gravity compensation springs were adopted in all deployment mechanisms during the deployment test. The deployment angle errors obtained were <0.01 °, which were good enough to maintain the antenna pointing accuracy required by the electrical performance. Figure 9 shows one of the response curves of the sinusoidal vibration test in the stowed configuration. The first resonance occurred at 25 Hz. The eigen frequencies obtained in the vibration tests were reduced by about 10% due to the flexibility of the test fixture. This effect was estimated analytically using two models, i.e. one with the fixture and the other without. These results are shown in Table 2. As for the fundamental eigen frequency, the difference between those two conditions was about 2 Hz. Then, it is concluded that the fundamental eigen frequency of the antenna without the fixture effect will be 27 Hz. The design goal of 30 Hz can be achieved easily with a slight design change to improve rib stiffness and the clamping condition of fixing bars. Since the vibration testing of the deployed configuration was difficult to conduct for the reflector, model tests on individual ribs were carried out. The measured fundamental frequencies were over 5 Hz for all ribs, which satisfied the requirement of more than 2 Hz.
Electrical and mechanical designs have been made for the deployable mesh antenna mounted on the 3 axis stabilized bus and stowed in rocket fairings with a 2 m i.d. Electrical, structural and thermal examinations have been made for this antenna. The electrical and structural designs and test results of the manufactured antenna are described here. It is verified from these results that the characteristics of the manufactured antenna well agree with the designed values. The system requirements can be achieved easily with a small design improvement. The thermal design and test have been made simultaneously and it is confirmed that this antenna has a good thermal performance. These results will be reported with the reliability test results for the deployment mechanisms. Acknowledgement--The authors would like to acknowledge
Dr Heiichi Yamamoto and Dr Tetsuo Yasaka for their continued guidance and encouragement. REFERENCES
1. K. Miyauchi, Communication equipment technology of Japanese domestic communication satellites. AIAA lOth Communications Satellite Conf., AIAA 84-0681 (1984). 2. R. V. Powell, A future for large space antennas. AIAA 7th Communications Satellite Conf., AIAA 78-0588 (1978). 3. R. A. Russell and T. G. Cambell, A technology development program for large space antennas. 31th IAF Congress, IAF-80A-33 (1980). 4. J. A. Fager and R. Garriott, Large-aperture extendabletruss microwave antenna. IEEE Trans. AP-17, 452-458 (1969). 5. B. C. Tankersley and H. E. Bartlett, Tracking and datarelay satellite single access deployable antenna. National
Telecommunications
Conference
Records
NTC-77, 19-4 (1977). 6. W. Schafer, H. Harbig, A. Roederer and K. Pontoppidan, Unfurlable offset antenna design for L and C-band application. AIAA 9th Communications Satellite Conf., AIAA 82-0443 (1982).