Tomoaki Toda

SCOPE is the magnetospheric explorer mission using a distributed sensing system to investigate space-time correlation of particle behaviors in the magnetotail. The mission needs an autonomous inter-satellite link system enabling commanding, data transfer, ranging, and timing control support for data sampling in unison in a distributed system. TDM/TDMA system has been proposed so as to fit to SCOPE specification. We have developed a simulator to validate our design for SCOPE and obtained successful results. As an instrument to work within a limited resources of small sized satellites like SCOPE, data link, ranging performance, timing accuracy satisfy requirements of SCOPE mission. We describe our inter-satellite link system and achievements obtained through the simulator experiments.

JAXA's next mission exploring magnetospheric region needs an onboard inter-spacecraft link system for both data transfer and observation support in formation. It has been designed as a set of spacecraft of four or five flying in formation. Ranging functions among spacecraft is very significant in this type of mission to keep a precise geometry of spacecraft formation. In our mission, two types of ranging are used properly. Since the system is based on a star topology with one mother spacecraft and daughters, a direct ranging is conducted using forward and return two-way link for branches between mother and daughters. The other ranging for the remaining branches among daughters is simply operated by exchanging their clock timing information synchronized with mother master clock. As this simplified ranging is done in the additional one slot of time division sequence, it greatly reduces difficulties of system modification when we need to increase and decrease the number of spacecraft in the project process. We have implemented this ranging system in our breadboard model to simulate inter-spacecraft links and have evaluated its operation under realistic conditions in orbit.

JAXA is currently planning the next generation magnetosphere observation mission called "SCOPE"(cross-Scale Coupling in Plasma universE). SCOPE aims at observing the Earth's magnetotail with 5 satellites flying in formation to fully resolve the temporary and spatial distribution of the magnetospheric phenomena. For this observation, the clock synchronization and relative distance measurement between the spacecrafts are essential. This paper describes an onboard relative ranging and clock synchronization algorithm, which applies a simplified formulation, using two-way and three-way phase differences as the filter inputs to construct the onboard system suit to the SCOPE mission.

SCOPE (cross Scale COupling in the Plasma universE) is a project designed as a successor of GEOTAIL and AKEBONO launched by ISAS/JAXA in 1992 and 1989 respectively. The scale coupling phenomenon in the Earth magnetotail has attracted many attentions after the work of the two precedent missions. SCOPE explores the vast area of magnetotail with a method of simultaneous multi-point probing by formation flying satellites to reveal complex behaviors brought by electrons, ions, and electromagnetic field in it. This mission demands satellites to be more interconnected via communication links than ever to approach to time-and-space resolved new facts in the magnetotail. In this paper, the outline of the communication system designed for JAXA's first formation flying mission: SCOPE will be presented. The key issues are the resource-limited developments for small satellites and the construction of an efficient wireless interlink enabling highly resolved correlation measurements in time-and-space.

The planetary exploration activity in ISAS was initiated by NOZOMI, Mars atmospheric surveyer launched in 1998. Based on the experience gained through this project, new planetary exploration programs have been investigated to lead our deep space activities in the 21stcentury. The Venus Climate Orbiter and Mercury Magnetosphere Orbiter are our missions selected for the first decade of the 21stcentury. In response to this decision, the review on communication capabilities of ISAS has been conducted from the viewpoint of reliability and cost-performance. The development of a new X-band transponder, research-oriented ground system, and turbo decoder test-bed was considered the most effective to support the missions. The X-band transponder is for the optimized and established onboard communication equipment meeting various demands of scientific missions in ISAS. The ground system directly works as a test-base of new communication technologies adopted in the new transponder and also serves as a demonstrator enabling prompt applications of laboratory technologies to missions in the future. The turbo coding scheme will be included in this ground system. The turbo decoder is under development so that its implementation in our ground station will be in time for the Mercury mission. In the following, we will discuss these developments and detailed configurations.

A semiconductor laser structure is proposed to introduce field effects in its active region. It has five layers of p-n-i-p-n with four electrical contacts to the doped layers, where the current injection into an inversely biased active region is based on the operation of two complementary bipolar transistors with their base-collector junction common. The inverse bias is useful to incorporate carrier transfer phenomena like Gunn effect in semiconductor lasers. Our analysis on the proposed lasers shows that its lasing operation is possible while applying a high electric field more than 10(6) V/m in the carrier transfer domain. (C) 2004 American Institute of Physics.

Optical antennas used for point-to-point communication in optical intersatellite communication must have high aperture efficiency. By means of the reflector surface shap ing method, it is possible to design an antenna with high aperture efficiency and low side lobes. However, the reflector surface becomes a nonspherical surface described by a higher-order polynomial and is very susceptible to errors in the manufacturing process. This paper proposes a shaped optical antenna whose shaped surface is described without a higher-order polynomial but with a nonspherical surface of the lowest order. The error characteristics are compared with those of the conventional shaped antenna. It is demonstrated that the proposed shaped optical antenna not only is more easily fabricated but also possesses almost identical error robustness to a nonshaped antenna. (C) 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 62-74, 2004; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ecja. 10145.

光衛星間通信のような点対点の通信で用いられる光アンテナは,高開口能率である必要がある.鏡面修整法を用いることにより,高開口能率,低サイドローブであるアンテナを設計することができるが,鏡面が高次の多項式を含む非球面となり,製作過程の誤差に対し極めて弱くなる.本研究では修整面が高次の多項式を含まないような修整光アンテナを提案し,誤差特性の改善をめざす.開口能率と独立なアンテナパラメータを変化させ,最も低次の非球面で構成できる修整光アンテナを設計し,従来の鏡面修整光アンテナと誤差特性の点で比較を行う,その結果,提案する修整光アンテナは従来の修整アンテナと比べて製作が容易になるだけではなく,非修整アンテナとほぼ同じ誤差耐性を有することを示す.

A shaped reflector antenna has a low tolerance to its various fabrication errors because its specific reflector shape needs high precision on the order of optical wavelength. This paper proposes a new design of optical antenna with a high tolerance against manufacturing errors by shaping a feeder-lens and a sub-reflector. Antenna parameters are optimized for each error and optical gain degradation. We compared the error tolerance of our optical antenna, a standard Cassegrain optical antenna, and a normal shaped reflectors optical antenna. The new optical antenna has better error tolerance than the normal shaped reflectors optical antenna and is competitive with the standard Cassegrain optical antenna. The designed new antenna's surface is so simple that the required manufacturing precision has become realistic.

Distributed-feedback (DFB) lasers were fabricated by using strained InGaAs quantum-wire (QWR) arrays on V-grooved GaAs substrates as an active grating. After characterizing the luminescence from the QWR's and parasitic quantum wells (QWL's), a DFB laser cavity incorporating such a QWR array with its emission wavelength matched to the Bragg wavelength was designed and fabricated. The wavelength selectivity of the DFB cavity was found to strongly support the QWR emission, and DFB lasing from QWR gain up to 145K; has been achieved under pulsed current, The emission from the parasitic QWL's was suppressed by the DFB filtering and the loss induced by coupling to radiation modes. The DFB cavity was shown to be essential for obtaining lasing from QWR's on V-grooved substrates.

Mass transport method has been developed as a high quality quantum wire (QWR) array formation technique in InP systems. It was demonstrated that strained InAsP QWRs with the lateral width less than 20 nm could be formed at the sharp bottom edge of InP V-grooves without any parasitic structures. Their emission peak wavelength and size were controllable by temperature and group V ambient pressure ratio. A distributed feedback (DFB) laser was fabricated by utilizing the mass-transported strained InAsP QWR array on GainAsP V-grooved substrates as an active grating. Lasing at 1.53 μm at 20 °C by pulsed current injection was accomplished. Record low threshold current density of 0.112 kA/cm2 was obtained in a broad area laser with a 100 μm-wide and 750 μm-long cavity.

InAsP quantum wires (QWRs) were sucsessfully fabricated on V-grooved InP substrate by using mass-transport method based on MOVPE. The quantum wire size is controllable by the mass-transport temperature, and its strain and composition are independently adjustable by the constitution of group V sources in the atmosphere during the mass-transport. The interface of QWR had good quality without any dislocations in spite of its large lattice mis-matching. Unlike the conventional growth on V-grooves no parasitic structures were found. Strong photoluminescence intensity at room temperature proves a good optical qualty and its polarization dependency peculiar to QWRs shows a good confinement of carriers with the fact of TEM observation.

Distributed feedback (DFB) quantum wire (QWR) lasers were fabricated on V-grooved substrates. After characterizing the wire emission using electro- and photoluminescence techniques, DFB laser cavities incorporating such QWRs with an emission wavelength matched to the Bragg wavelength were designed and fabricated. The selectivity of lasing wavelength of the DFB cavity was used to obtaining DFB operation at the emission wavelength of the wire up to 145K under pulsed conditions. The emission from the parasitic quantum well structures was suppressed due to the forbidden DFB gap.