ETS-VIII (Engineering Test Satellite-VIII) / Kiku-8
ETS-VIII is an advanced JAXA (Japan Aerospace Exploration Agency) technology demonstration satellite with the aim to develop and verify the world's largest geostationary satellite-bus technology, considered to be necessary for space missions at the beginning of the 21st century. In Japan, the mission is also referred to as Kiku-8. The mission objectives are to conduct orbital experiments on the following structures/systems: (the first three are required to realize mobile satellite communications with hand-held terminals, similar to popular cellular phones). 1) 2)
• LDR (Large-scale Deployable Reflector) developed by JAXA. A modular structure is employed to meet the requirements of reflector surface preciseness (2.4 mm rms surface precision) and antenna diameter expendability. Each LDR consists of 14 hexagon-shaped modules. Once deployed, each reflector forms a parabola surface with expanding metal mesh (19 m x 17 m in outside dimension). Each module has a deployable truss structure. ETS-VIII is equipped with two LDR modules, one of data transmission and the other for reception. During launch the LDR system is packed in a cylindrical container of size 1 m diameter by 4 m in length.
• HPT (High-Power Transponder), developed by the former ASC (Advanced Space Communications Research Laboratory). Since 2004, the new name is NICT (National Institute of Information and Communications Technology), Tokyo.
• OBP (On-Board Processor), provided by NICT.
• Moreover, the ETS-VIII spacecraft a high precise clock system for the satellite positioning experiments was developed by JAXA and NICT. 3)
Figure 1: Artist's view of the ETS-VIII spacecraft in orbit (image credit: JAXA)
The satellite features a 3-ton class bus comprising the satellite body, the EPS (Electric Power Subsystem), C&DH (Command and Data Handling) subsystem, a thermal control subsystem, AOCS (Attitude Orbit Control Subsystem), and a propulsion module. The S/C shape is a rectangular box with deployable solar paddles. The spacecraft was manufactured and integrated at MELCO (Mitsubishi Electric Corporation) Kamakura Works, Kamakura-City, Japan using the DS2000 platform. 4) 5) 6)
The spacecraft design employs a number of features such as:
• A light structure to improve the payload to bus system ratio to 40% from the conventional 30%
• The bus system consists of several modules to reduce development time through concurrent work to integration
• The bus power supply voltage was changed from the conventional 50 V to 100 V for greater electrical power
• The MIL-STD-1553B data bus standard is used for commonality. In addition, the CCSDS packet protocol suite was chosen for all data communication with the ground segment
• The thermal subsystem uses heat pipes to connect the north and south panels of the satellite thereby expanding the effective radiation surface
• Use of an attitude control system with fault-tolerant functions and in-orbit reprogramming capability.
ETS-VIII is three-axis stabilized, the accuracy of the AOCS is: roll/pitch axis = ±0.05º max., yaw axis = ±0.15º max. The AOCS employs an Earth sensor assembly, a sun sensor and an integrated rate gyro assembly for attitude sensing. Actuation is provided by four reaction wheels, each of 50 Nms, in a skewed arrangement. In addition, 13 accelerometers are installed to monitor the dynamic behavior of the deployed structure. The MIL-STD-1553B data bus is being used for all onboard data handling. The OBC design supports autonomous FDIR (Fault Detection, Isolation and Reconfiguration) functions.
The S/C mass is 2900 kg at the beginning of mission life with a payload mass is 1100 kg. The EPS (Electric Power Subsystem) provides 7.5 kW with a regulated 100 V of bus voltage. The NiH2 batteries provide a capacity of 100 Ah for eclipse operations. The S/C bus has a design life of 10 years, the mission design life is three years. The spacecraft has been built at Mitsubishi Electric of Tokyo as prime contractor to JAXA.
The overall length of the spacecraft is 40 m measured along the axis of the solar panels, and 40 m measured along the axis of the two LDRs (when deployed). Two propulsion systems are used: a) an apogee (bi-propellant) engine in the 500 N class with 22 N thrusters (used for attitude control and E-W station-keeping), and b) a Xenon ion engine providing a thrust of 25 mN, two ion engines are used for N-S station-keeping. 7) 8) 9) 10) 11) 12) 13)
Figure 2: Photo of the ETS-VIII Xenon tank (image credit: Mitsubishi, JAXA)
IES (Ion Engine System): JAXA and MELCO developed a 20 mN class xenon ion engine system for the spacecraft. IES can operate for more than 16,000 hours at an average thrust of over 20 mN and an average specific impulse of over 2,200 s. IES was used for north-south station-keeping of Kiku-8.
Figure 3: The ETS-VIII deployed S/C configuration and deployed dimensions (image credit: JAXA)
Table 1: Overview of some spacecraft parameters
Figure 4: Block diagram of ETS-VIII (image credit: JAXA)
Figure 5: Photo of the ETS-VIII spacecraft in the integration facility (image credit: JAXA)
Launch: The launch of ETS-VIII took place on Dec. 18, 2006. Use of the H-IIA F11 launch vehicle from the Tanegashima Space Center, Japan.
Orbit: Geostationary orbit of ETS-VIII at 146º E longitude (altitude of 35,786 km above the equator).
RF communications: TT&C communications are provided in S-band. All data transmission is done with CCSDS protocols.
Table 2: Specification of the onboard processors
Table 3: RF subsystem performance
Figure 6: Schematic view of the deployed configuration of ETS-VIII (image credit: NICT)
Legend to Figure 6: The physical size of the reflector is 17 x 18 m, and the number of array elements of the Tx/Rx primary feed is 31. The Tx frequency band is 2.5 GHz and Rx frequency band is 2.6 Ghz (S-band).
• The ETS-VIII / Kiku-8 spacecraft is operating nominally in 2014. 14)
• The ETS-VIII / Kiku-8 spacecraft is operating nominally in 2013.
• The ETS-VIII / Kiku-8 spacecraft is operating nominally in 2012 in its 6th year on orbit (the mission design life is 3 years). 15)
• 2011: The project is reporting the following experimental results and anomalies of antenna performance: 16)
1) The actual beam direction is different from the calculated result; the angle has shifted by ~ 0.2º to the east from the calculated result.
2) The radiation patterns do not satisfy the designed value (-20 dB specifications level) of side lobe.
3) A daily variation of the beam direction is observed.
In the analysis, the project team argues that these anomalies are caused by a mounting angle error and the surface distortion of the reflector. With these large antennas, the thermal distortion error can have serious implications, causing beam pointing errors, distortion of the beam shape, and increasing sidelobe levels.
An example of the temperature telemetry of a reflector during an eclipse is shown in Figure 7. During the eclipse, variation in temperature is large and drastic. Here, M5, M10 and M12 denote the temperature sensor numbers at reflector surface.
Figure 7: Temperature variation of reflector (image credit: NICT)
Figure 8 shows the time variation in beam direction. Here, the solid line shows nominal position of the beam (before eclipse) and the broken line shows the pattern in an eclipse. The times shown in Figure 8 are the times during eclipse.
In conclusion it can be stated that thermal distortion errors of large reflector antennas represent a serious factor in orbit - involving beam direction errors, distortion of the beam shape, and increasing side-lobe levels.
• On March 24, 2011, JAXA began a satellite communication connection using the Engineering Test Satellite VIII "KIKU No. 8" (ETS-VIII) to support disaster measures following the Tohoku Region Pacific Ocean Coastal Earthquake. 17)
• ETS-VIII (Kiku-8) spacecraft and its payload are operating nominally in 2010.
• The KIKU-8 satellite is being used to demonstrate the effectiveness of satellite communications for the disaster management support and relief requirements. JAXA joined in disaster prevention training sessions held by local governments and demonstrated emergency communications experiments via KIKU-8 with the portable and handheld terminals. 18) 19)
• The IES (Ion Engine System) was operated in orbit for about two and a half years for north-south stationkeeping. The thruster operation time is more than 3,000 hours.
• The LDR antenna system has demonstrated the expected electrical performances in orbit. The communications experiments using the LDR antenna system have achieved steady results (Ref. 23).
• Kiku-8 provided nominal operations starting in May 2007. Many types of experiments and demonstrations are being performed. The in-orbit electrical performance verification for the LDR antenna system was one of these experiments. This radiation pattern verification is continuously being conducted in each season in corporation with NICT, the developers of the feed system of the antenna system. The radiation pattern is calculated from the ground station receiving signal levels from the satellite while the beam is scanned systematically pitching or rolling the satellite. 20) Ref. 23)
• In the IOT (Initial Orbit Test), the radiation pattern for the S-band antenna system including the LDR was measured.
• On-orbit system identification experiments were conducted during the initial check-out phase of the ETS-VIII to estimate its dynamics. 21)
Table 4: Check-out events for on-orbit system identification of ETS-VIII
• On Jan. 9, 2007, a maneuver was started to place the spacecraft in its final GEO orbit at 146º E longitude.
• On Dec. 27, 2006, JAXA shifted the attitude attitude control mode of ETS-VIII to the regular control mode. All functions of the satellite have been verified to be normal after the control mode shift.
• Successful deployment of the LDR (Large-scale Deployable Reflector) took place on Dec. 25 and 26, 2006. This was confirmed by telemetry and imagery (the deployment behavior in close-up and distant view was taken by two onboard cameras as shown in Figure 9). 22)
Figure 9: TX-LDR successful deployment in orbit (full deployment in distant view), image credit: JAXA
Mobile satellite communications and broadcasting experiments:
The objective of ETS-VIII is to conduct orbital experiments on mobile satellite communications and high-speed packet communications, providing voice/data communications with hand-held terminals in the S-band. For these experiments, a 31-element active phased array feeder of 400 W gross output and a beam forming network had been developed to synthesize signals into several beams to cover some parts of the Japan Islands. The onboard processor switches links of cellular phones and high-speed packets, enabling us to establish a single-hop communication link with the ETS-VIII without ground switchboards along the path.
S-band communications and broadcasting experiments are being conducted to demonstrate a mobile satellite communications and broadcasting system technologies with small-scale ground terminals (such as hand-held terminals). These experiments employ the following devices:
LDR (Large-scale Deployable Reflector):
The entire spacecraft structure is dominated by the two large deployable antenna reflector structures, each of size 19.2 m x 16.7 m with a 13 m aperture. Each mesh deployment antenna consists of 14 modules. Each module in turn consists of a gold-plated Molybdenum mesh surface, a spatially determined cable network, and a deployable truss as supporting structure. The entire antenna system fits in a stow-volume of 1 m diameter x 4 m in height. 23)
Each LDR module is a hexagonal truncated pyramid, whose dimension is optimized by considering some design requirement such as weight, natural frequencies, a stowed size, and rigidity. Modular structures are easy to handling, testing and adjusting. The basic concept of the modular mesh deployable antenna was proposed by NTT (Nippon Telegraph and Telephone Corp.).
Figure 10: View of one LDR mesh system (image credit: JAXA)
The phased array feeder systems are combined with the LDRs to create multiple steerable MSS (Mobile Satellite communication Systems) and to support mobile BSS (Broadcasting Satellite System) experiments (3). The transmission side feeder consists of 31 solid state power amplifiers (300 W in gross output), and the receiving side feeder of 31 low noise amplifiers. The on-board beam-forming network controls the amplitude and phase of the signals to/from the feeder elements to create multiple steerable beams and to form the desired beam patterns.
Onboard signal switching:
Two sets of onboard baseband switching equipment are installed to realize onboard signal routing. One is an on-board processor (OBP), which is designed to perform voice channel switching among mobile users or between mobile users and ground network users and has 500 channel capacity. The other is an onboard packet switch (OPS) for high-speed packet data communications.
Table 5: Design specifications of the antenna reflectors
Figure 11: Alternate illustration of the deployed spacecraft (image credit: JAXA)
Figure 12: Block diagram of mobile satellite communications payload (image credit: JAXA)
Satellite positioning experiments:
Positioning experiments (in S- and L-band) are conducted to study basic satellite positioning system characteristics and to demonstrate the feasibility of new satellite positioning system concepts (consisting of MEO and GEO constellation elements). A high-accuracy time signal, which is similar to the GPS data, created by an atomic cesium frequency standard on the satellite is transmitted. Furthermore, the TCE (Time Comparing Equipment) is used to conduct precise time comparison between the onboard atomic clock and the ground reference clocks. High-accuracy orbit determination is supported by SLR (Satellite Laser Ranging) stations.
Table 6: Specification of the positioning system
In the experiment, time signals from two sources, namely the GPS constellation and from the on-board atomic clock are used to determine the position of the satellite. The intend is to reduce the number of spacecraft in the constellation of a future navigation system (if sufficient accuracy can be achieved by this method of orbit determination).
LRRA (Laser Retroreflector Array):
The objective is to support SLR activities for precise orbit determination. The LRRA consists of 36 corner-cubes which are 4.1 cm in diameter, respectively. The array structure is aluminum alloy and the corner cubes are constrained to allow for the differential thermal expansion of the structure and the quartz corner cubes. The array assembly has a mass of less than 3.1 kg. The array is 26 cm length, 30 cm width and 5.5 cm in height. 24) 25)
Figure 13: Illustration of the LRRA (image credit: JAXA)
The 36 individually serialized corner cubes are high homogeneity Suprasil-1(quartz). The individual corner cubes are 4.1 cm diameter and optimized for the velocity aberration of the satellite as well as for a wavelength of 5320 Ä. The surface flatness is 1/10 wavelength at 5320 Ä. The reflectivity is specified to exceed 75% at 5320 Ä. The net optical efficiency of the prism is specified to exceed 95% at 5320 Ä. Here, the net optical efficiency is defined as the probability of receiving one or more reflected photoelectrons at a ground station per one pulse of laser emitted from the ground station.
Table 7: Summary of LRRA parameters
Figure 14: The satellite coordinate system of the ETS-VIII / LRRA installation position (image credit: JAXA)
LRRA is installed on the top of ETS-VIII’s antenna-tower (Figure 14). The attitude of ETS-VIII affects the position and the direction of LRRA. The performance of ETS-VIII attitude orbit control subsystem is as follows:
Attitude control error (3σ): Roll (< ±0.05º), Pitch (< ±0.05º), Yaw (< ±0.15º).
ETS-VIII LRRA is developed based on the performance of SLR stations Koganei (NICT) and Moblas-5 (NASA).
To make a maximum use of the LDR and to verify the ETS-VIII mobile satellite communication system, JAXA has developed two types of small ground terminals for communications experiments. One is a portable terminal shown in Figure 15 and the other is a handheld terminal shown in Figure 16.
The portable terminal is a briefcase size and is able to communicate with other portable terminal directly via the satellite. Since the portable terminal uses the TCP/IP interface, data from a PC can be transmitted directly with data rates ranging from 64 kbit/s to 1.5 Mbit/s.
Figure 15: Photo of the portable terminal (image credit: JAXA)
Figure 16: Photo of the handheld terminal (image credit: JAXA)
The handheld terminal consists of a general purpose PDA terminal called “Ubiquitous Communicator” and a satellite communication card. The satellite communication card uses satellite communication antennas and a GPS antenna. The signals from/to the satellite are being processed in this card. The satellite communication card is simply inserted into the PDA and interfaced with the USB interface. The data rates are 50 to 400 bit/s for transmission and 1.6 to 12.8 kbit/s for reception.
LDREX-2 (Large Deployable Reflector Small-sized Partial Model 2)
JAXA tested the LDR deployment sequence by flying the LDREX-2, a small-size model of LDR as a secondary payload on the Ariane 5ECA launcher from Kourou on Oct. 13, 2006 (UTC). The primary payloads on this flight were DirecTV-9S, a US communications satellite, and Optus D1, an Australian communications satellite.
LDREX-2, designed by JAXA and build by NEC Toshiba Space Systems Ltd., is a deployable antenna reflector experiment on scale 1/2 representative of the large LDR antenna of the future technology satellite ETS-VIII. 26)
LDREX-2 was mounted onto the ASAP (Ariane Structure for Auxiliary Payloads) platform on Ariane-5. The payload had a mass of 211 kg, and a folded size of 0.7 m x 0.6 m x 1.9 m (deployed span in orbit of 6.5 m).
Figure 17: Deployed structure concept of LDREX-2 on the ASAP ring (image credit: JAXA)
The two spacecraft on this flight were ejected successfully into GTO (Geosynchronous Transfer Orbit). LDREX-2, at the bottom of the payload stack, remained attached to the ESC-A upper stage.
Figure 18: Stowed configuration of the LDREX-2 and the ASAP ring (image credit: JAXA)
On Oct. 16, 2006, JAXA confirmed the antenna deployment by images acquired at the Malindi Station in the Republic of Kenya. The images were recorded by cameras mounted on the launch vehicle.
Figure 19: Image of the deployed LDREX-2 structure (image credit: JAXA)
Aeronautical Earth station:
The aeronautical Earth station is composed of an APAA (Active Phased Array Antenna), modulator/demodulator (modem), up-converter (U/C), and down-converter (D/C). The APAA has 18 microstrip antenna elements and can be installed on a vehicle very easily. The main specifications of the APAA and modem are shown in Table 9. The total output power of the APAA is about 25 W. The beamwidth of the main lobe for the APAA antenna pattern is about 30º. The APAA was installed on the top of a Gulfstream II aircraft and was covered with a radome, which was used for the Ka-band aeronautical satellite communications experiment. The modem has a changeable transmission rate from 5 kbit/s to 3 Mbit/s. Its modulation techniques are the BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying) and offset QPSK. 27)
Table 8: Major specifications of the aeronautical Earth station
Aeronautical Mobile Satellite Communications Experiment:
The base station is located at the Kashima Space Technology Center, Ibaraki, Japan. It has a parabolic antenna with a diameter of 3.8 m for the S-band frequency. The diagram of the experimental system is shown in Figure 20. Table 9 shows an example of the link budget for the aeronautical mobile satellite communications experiment. The quality of the downlink is superior to that of the uplink in the case of the return-link. The total C/No of the return-link is about 56 dBHz, which is almost the same as that of the uplink C/No.
Figure 20: Experimental system for data transmission (image credit: NICT)
Table 9: Example of link budget of return-link
Satellite tracking performance in flight: The APAA has a satellite tracking function that uses the open-loop method or the closed-loop method. In the open-loop method, the APAA receives position signals from the global positioning system receiver and attitude signals from the aircraft, and it calculates the satellite direction using those data. On the other hand, the closed-loop method uses the step-track system. The APAA has a satellite tracking performance of over 30º/s.
Figure 21 shows the receiving level during one rotation in the case of the 20 degree turning flight. The APAA has theoretically an omnidirectional antenna pattern for the azimuth direction, and the receiving level in the case of the turning flight has a sinusoidal wave curve during one rotation; however, the APAA actually has different antenna gains for the azimuth direction. Therefore, the receiving level curves, which are shown in Figure 21, are a little different from the sinusoidal wave curves. Figure 21 (left and right) show the signal level in the case of the open-loop and closed-loop satellite tracking, respectively. In the closed-loop, the beam direction of the APAA always changes because of the step-track system. Therefore, the variation of the signal level in the case of the closed-loop is larger than that in the case of the open-loop.
Figure 21: Left: Received power level in case of open-loop; Right: Received power level in case of closed-loop (image credit: NICT)
Data transmission performance: The transmission rate of 10 kbit/s, which was a low bit rate, was selected for the experiment because the expected maximum C/No was only about 56 dBHz. The QPSK was used as the modulation technique, the length of the packet signal was 100 Byte, and the throughput of the packet signals for the C/No was measured. The results of the packet data transmission test are shown in Figure 22. The circles and triangles indicate the data in the case of static conditions and level flight, respectively. The measuring period shown by one circle in static conditions is several minutes; on the other hand, the measuring period shown by one triangle in level flight is 10 seconds. Although the data in level flight have some differences because the measuring period was short, the throughput performance of the packet signals in the case of level flight was almost the same as that in the case of static conditions. The crosses show the data in the case of the 20º turning flight. The measuring period shown by one cross in the turning flight is also 10 seconds. The results show the throughput performance of the packet signals in the case of the 20º turning flight was about 2 dB less than that in the case of static conditions.
Figure 22: Schematic view of the throughput performance (image credit: NICT)
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.