2 Overview of the Optical Inter-orbit Communications Engineering Test Satellite (OICETS) Project

ARAI Katsuyoshi

The Optical Inter-orbit Communications Engineering Test Satellite (OICETS “KIRARI”) is an experimental technology satellite aiming the orbital demonstration of optical communication with the ESA (European Space Agency) ARTEMIS (Advanced Relay and TEchnology Mission Satellite) geosynchronous satellite. Its main orbit demonstrations are laser acquisition and tracking technology, on-orbit performance degradation of optical devise and system, and future international inter-orbit operation of optical communications technology. OICETS started the project in 1995, was launched at Baikonur in August 2005, after the AR- TEMIS geosynchronous orbit acquisition. OICETS made success of two world first demonstra- tions in the laser optical communications. One was two-way communication with ESA ARTE- MIS in 2005. Another was communication with the NICT ground station in 2006. This paper describes the overview of OICETS project such as development status, key technologies and launch and experimental results. Keywords Optical Inter-orbit communication, Low earth orbit satellite - optical ground station, Laser, International inter-orbit operation, International cooperation

1 Introduction ture technology for the efficient transmission of a tremendous amount of observation data. Radio wave communications support vari- Just like optical fibers for communication net- ous space activities. They are used for exam- works on the ground, laser beams can be used ple to transmit remote sensing data from an in space to transmit a large volume of data. earth observatory satellite, transmit images of Inter-orbit communication technology, distant planets from an exploration satellite, which is used between a low earth orbit satel- and exchange information between satellites lite, such as an earth observatory satellite or in orbit. As earth observation from space and International Space Station (ISS), and data re- other space activities become more active, the lay satellites (geostationary satellite), are im- resolution of observation sensors mounted in portant technologies to support various space earth observatory satellites should be im- activities including the acquisition of observa- proved and the data volume should increase tion data from earth observatory satellites or ［1］. However, due to a limitation of the fre- the continual securing of communication lines quencies that can be used for space communi- from the ISS. Optical inter-orbit communica- cations, radio wave interference is becoming a tion technology using laser beams is a key problem. Optical communications using laser technology for future data relay satellites as it beams has therefore attracted attention as a fu- not only improves the speed and capacity of

ARAI Katsuyoshi 5 data transmission drastically but also reduces test satellite for elementary technologies for the size and weight of communication antenna. the load map of satellite communications and In-orbit optical communication technology broadcasting. using laser beams has drawn attention as a fu- Figure 1 shows an image of optical inter- ture technology. To demonstrate it, the Japan orbit communications between the OICETS Aerospace Exploration Agency (JAXA) began and ARTEMIS and Fig. 2 that of an optical to develop the Optical Inter-orbit Communica- communications experiment with an optical tions Engineering Test Satellite (OICETS). ground station. The configuration of the The satellite was expected to play a role as a OICETS in orbit and its major performance

Fig.1 Image of optical inter-orbit communica- Fig.2 Image of optical communications experi- tions experiment between the OICETS ment made with an optical ground station and ARTEMIS. (The satellite on the near of the National Institute of Information and side is the OICETS) Communications Technology (NICT)

Dimensions Satellite body: 0.78 m × 1.1 m × 1.5 m (height) Total height including optical antenna: 2.93 m Total length including solar array paddle: 9.36 m Weight About 570 kg at launch Orbit Circular orbit: Altitude: 610-550 km Orbital inclination: About 98° Designed life 1 year

Fig.3 Confi guration and major performance of the OICETS on orbit

6 Journal of the National Institute of Information and Communications Technology Vol. 59 Nos. 1/2 2012 details are presented in Fig. 3. advanced experience. The ARTEMIS was launched in July 2001 but it turned out that the 2 Development history deployment of the geostationary satellite to or- bit was significantly delayed due to trouble In an administrative meeting between Ja- with the launch vehicle. Since it was necessary pan and ESA in 1992, discussions started for a to see whether the ARTEMIS could be made joint experiment of optical communications. geostationary, the Space Activities Commis- Optical inter-orbit communications were ex- sion decided in August 2001 to postpone the pected to be used for data relay satellites and launch of the OICETS. hence mutual operability was important (be- However it turned out that, after ESA cause the space agencies could share the com- worked hard, the ARTEMIS was able to be munication service by making a common put into the geostationary orbit in the begin- communication method). In this situation, ac- ning of 2003. Then, JAXA made a proposal to tual in-orbit demonstration of the technology the Space Activities Commission for launch- in a practical situation was required and inter- ing the OICETS in 2005, considering the fact national collaboration was needed to conduct that the optical communication device in the the project in a limited schedule and utilize ARTEMIS would end its design life in 5 years costs efficiently. (in July 2006). The Commission checked if Technological coordination began in 1993 the initial significance and purpose were still using ESA’s geostationary satellite ARTE- maintained in the project and discussed the va- MIS. In December 1994, the commissioner of lidity of the project including the launch vehi- ESA and the president of the National Space cle. As a result it was appreciated once again Development Agency of Japan (currently that the initial significance of the demonstra- JAXA) exchanged a MOU with each other tion of optical inter-orbit communications in about optical inter-orbit communications ex- space was still valid, that early demonstrations periments, which was the start of the joint ex- of optical communications in space were still periment project to be conducted through in- important for future technologies of Japan, and ternational cooperation. that the techniques could be applied to high- JAXA began the development of the precision ranging and other technologies. On OICETS in 1995 and the detailed technologi- the other hand, the discussion on the launch cal coordination with ESA. Although interna- vehicle was continued in order to select the tional technological coordination was difficult, most appropriate launch method with an aim JAXA learned a lot from Europe which had to launching the OICETS in 2005. Through

Fig.4 OICETS development schedule (from start of development to launch)

ARAI Katsuyoshi 7 the discussions on the selection of the launch sion rate, reduces transmission power, and vehicle, it was found that the first stage of the softens requirements for receivers. J-Ⅰ rocket could not be used due to an accident (2) The size, weight and power consumption with the H-ⅡA rocket No. 6, and H-ⅡA rocket of communication devices can be reduced. could not be used as it was to be used to (3) The attitude is highly stable due to low at- launch another satellite, M-V rocket could not titude disturbances from the operation of small be used due to a launch environment problem, optical antenna. and GX rocket could not be used as it was still (4) EMI (electromagnetic interference) can be under development. In this difficult situation, reduced. the possibility of using a foreign rocket was (5) The systems are highly resistant to interfer- examined as the second best way. In these dis- ence and interception of communications and cussions, the actual flight record and reliability advantageous in terms of communication of the rocket launching, the compatibility of confidentiality. the schedule, and delivery problems of the sat- ellite were taken into account. As a conse- Figure 5 compares actual radio wave com- quence, a plan for launching the satellite with munications satellites and optical inter-orbit the Russia-Ukraine Dnepr rocket from the communications satellites. Baikonur Cosmodrome in 2005 was proposed To take advantage of optical inter-orbit in December 2004 to the Space Activities communications, there are some technical Commission, which then approved the propos- problems to be solved. The maximum distance al. Figure 4 shows the development schedule between a geostationary satellite and a low of the OICETS from the start of development earth orbit satellite is 40,000 km. For satellites to the launch. that are far away from each other to transmit and receive laser beams to a precision of sev- 3 Demonstration experiment in eral micro radians, high-precision optical de- orbit vices and technology for their accurate control are necessary. We demonstrated with the Compared to radio wave communication OICETS the key element technologies, systems, optical communication systems have checked performance degradation in the space the following advantages: environment, and obtained data for practical (1) High antenna gain increases data transmis- use.

Fig.5 Comparison of radio wave communications and optical communications

8 Journal of the National Institute of Information and Communications Technology Vol. 59 Nos. 1/2 2012 The major items of the in-orbit experi- 4 Launch ments are shown below: (1) Fine tracking and pointing experiments As mentioned in Section 2, the launch ve- - Bidirectional optical inter-orbit commu- hicle was changed from the J-Ⅰ rocket at nications are performed and their major Tanegashima to the Dnepr rocket at the Bai- key element technologies are demonstrat- konur Cosmodrome. Although there were a ed. number of problems to be solved such as tech- (2) Optical inter-orbit communications experi- nological problems, satellite delivery prob- ments lems, and problems of working in an unfamil- - Optical inter-orbit communications ex- iar launch site, not only those who were periments are performed many times to ob- involved in the development of the satellite tain statistical data for practical use. but also those who were involved in the (3) Evaluation experiments for optical devices ground system collaboratively worked on the - Degradation characteristics of major opti- hardware changes of the satellite, adjustment cal devices are examined in space environ- with the launch vehicle, and redevelopment of ment. a tracking system and experiment system for a (4) Satellite micro vibration measurement ex- short period of time. About two months before periments the launch, the satellite was delivered to the - Micro vibration of the satellite is mea- Baikonur Cosmodrome in Kazakhstan and sured to evaluate its influence on optical preparation work for the launch began. It was inter-orbit communications the first time for Japan to launch a JAXA sat- (5) Optical ground station experiments ellite from the Baikonur Cosmodrome. It was (Additional experiments after launch) also the first time using the Dnepr rocket. We - Experiments of optical communications therefore made prior surveys and checking of between the OICETS and ground stations the rocket and launch site. Since not only peo- are conducted. ple but also check-out equipment were re- stricted to enter the Baikonur Cosmodrome,

Fig.6 Group picture after launch

ARAI Katsuyoshi 9 necessary preparatory work was conducted as tween the OICETS and an NICT optical much as possible. These were very difficult ground station were conducted in March 2006. but we were able to get over the highest barri- Although it was expected to be quite difficult ers through the effort and enthusiasm of the for the specifications of the satellite, the opti- people involved. cal communication between the low earth orbit On August 24, 2005, the OICETS was satellite and the ground station was success- launched. It was deployed to orbit as sched- fully performed for the first time in the world uled and operated according to plan after sepa- by utilizing ingenious techniques for the oper- rating from the launch vehicle. The successful ation and by taking advantage of the satellite’s launch of the satellite was a moment when the own capability. After the public release of the one-year effort was rewarded ［2］. Figure 6 success of optical communications with the shows a commemorative group picture after optical ground station, we received proposals the launch. for joint experiments from various space agen- cies. In June 2006, we also succeeded in opti- 5 In-orbit experiments cal communications with a transportable opti- cal ground station from the German Aerospace The OICETS was put into the orbit at an Center (DLR). From October 2006, the project altitude of 610 km and an orbital inclination entered the second stage of using the satellite. 97.8°. After the OICETS was separated from In this stage, degradation data was successive- the launch vehicle, the operations, such as de- ly collected to evaluate the life of the bus ployment of the solar array paddles, were con- equipment (wheel, etc.) and optical communi- ducted as scheduled and critical operations cation equipment. In March 2008, the ex-post were finished on August 25. The operational evaluation of the Space Activities Commission check (initial functional check) of the bus indicated that the OICETS project “performed equipment and mission equipment of the satel- as expected.” The satellite operation was sup- lite in orbit were carried out for about three posed to be terminated after the ex-post evalu- months. The optical inter-orbit communication ation. However, since strong requests for opti- equipment was calibrated and the automatic cal communications experiments between the tracking and pointing function was checked OICETS and optical ground stations were re- using the star Sirius. On December 9, 2005, ceived from the NICT and foreign space agen- the world’s first experiment of bidirectional cies, additional experiments were performed optical inter-orbit communications with the in addition to the second stage. ARTEMIS was performed successfully during The OICETS finally ended its operations the initial functional check. It had been about on September 24, 2009 after the additional ex- 10 years since the start of development of the periments of communications with all of the OICETS, and we finally succeeded in the dem- foreign optical ground stations. onstration of optical inter-orbit communica- The experiment results of the OICETS in tions using laser beams, which had seemed orbit are described in “3-2 Optical Inter-orbit impossible at the start of development. Then Communication Experiment between OICETS the project entered a stationary stage, where and ARTEMIS”. bidirectional optical inter-orbit communica- Major operations of the satellite and a tions experiments between the OICETS and summary of the experiments after launch are the ARTEMIS were conducted for the planned shown in Fig. 7［3］ . mission period of about a year. Since optical inter-orbit communications between the 6 Conclusions OICETS and the ARTEMIS could be per- formed with no particular problems, additional The launch of the OICETS was consider- experiments of optical communications be- ably delayed due to the change of schedule of

10 Journal of the National Institute of Information and Communications Technology Vol. 59 Nos. 1/2 2012 Fig.7 Summary of in-orbit experiments of the OICETS the ARTEMIS and the change of the launch stage of using the satellite, we contributed, vehicle. However, we succeeded in the world’s with the efforts of the NICT, to optical com- first bidirectional optical inter-orbit communi- munications experiments with the optical cations experiments owing to the efforts and ground stations of foreign space agencies. I enthusiasm of the people involved. We also hope that the results of the optical communica- succeeded in optical communications between tions experiments will greatly contribute to fu- a low earth orbit satellite and an optical ground ture space development and that Japan can station. We could thus achieve significantly maintain a leading position in optical commu- greater results than expected in the initial plan nications in space. for in-orbit experiments. Also in the second

References 1 Morio Toyoshima, “Tracking, pointing and directing technologies for inter-orbit laser communications — Comparison and use of radio wave communication system and optical communication system—,” Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 88, No. 4, pp. 276–283, April 2005. 2 Toshihiko Yamawaki, Nobuhiro Takahashi, and Katsuyoshi Arai et al., “Launch of Kirari (OICETS) from Bai- konur,” ISTS2006-j-06, 2006. 6. 5–9. 3 Katsuyoshi Arai, “Development and in-orbit experiment of Optical Inter-orbit Communications Engineering Test Satellite (OICETS) ‘Kirari’,” Communication Society Magazine of the Institute of Electronics, Information and Communication Engineers, Winter issue No. 3, 2007.

(Accepted March 14, 2012)

ARAI Katsuyoshi 11 ARAI Katsuyoshi Director, Ground Facilities Department, Japan Aerospace Exploration Agency Spacecraft Development Project (BSE, BS-2, MDS-1, OICETS), JEM Develop- ment Project

12 Journal of the National Institute of Information and Communications Technology Vol. 59 Nos. 1/2 2012