冨木 淳史

<p>A Fault Detection, Isolation, and Recovery (FDIR) algorithm for attitude control systems is a key technology to increasing the reliability and survivability of spacecraft. Micro/nano interplanetary spacecraft, which are rapidly evolving in recent years, also require robust FDIR algorithms. However, the implementation of FDIR algorithms to these micro/nano spacecraft is difficult because of the limitations of their resources (power, mass, cost, and so on). This paper shows a strategy of how to construct a FDIR algorithm in the limited resources, taking examples from micro deep space probe PROCYON. The strategy focuses on function redundancies and multi-layer FDIR. These ideas are integrated to suit the situation of micro/nano interplanetary spacecraft and demonstrated in orbit by the PROCYON mission. The in-orbit results are discussed in detail to emphasize the effectiveness of the FDIR algorithm. </p>

<p>SLIM (Smart Lander for Investigating Moon) is the Lunar Landing Demonstrator which is under development at ISAS/JAXA. SLIM demonstrates not only so-called Pin-Point Landing Technique to the lunar surface, but also demonstrates the design to make the explorer small and lightweight. Realizing the compact explorer is one of the key points to achieve the frequent lunar and planetary explorations. This paper summarizes the preliminary system design of SLIM, especially the way to reduce the size.</p>

<p>Precise determination of antenna phase centers is crucial to reduce the uncertainty in gain when employing the three-antenna method, particularly when the range distances are short-such as a 3-m radio anechoic chamber, where the distance between the phase centers and the open ends of an aperture antenna (the most commonly-used reference) is not negligible compared with the propagation distance. An automatic system to determine the phase centers of aperture antennas in a radio anechoic chamber is developed. In addition, the absolute gain of horn antennas is evaluated using the three-antenna method. The phase centers of an X-band pyramidal horns were found to migrate up to 18 mm from the open end. Uncertainties in the gain were evaluated in accordance with ISO/IEC Guide 93-3: 2008. The 95% confidence interval of the horn antenna gain was reduced from 0.57 to 0.25 dB, when using the phase center location instead of the open end. The phase centers, gains, polarization, and radiation patterns of space-borne antennas are measured: low and medium-gain X-band antennas for an ultra small deep space probe employing the polarization pattern method with use of the horn antenna. The 95% confidence interval in the antenna gain decreased from 0.74 to 0.47 dB.</p>

PROCYONは,超小型衛星による小惑星フライバイ探査ミッションを目的として,はやぶさ2のピギーバック搭載機会である2014年12月の打ち上げを目指している.超小型衛星による深宇宙探査ミッションは,大型衛星とは異なる信頼性基準,コストのバランスによって成立させる必要がある.特に搭載重量や発生電力の制約条件は大きく,従来の宇宙用通信コンポーネントの設計概念を大きく変えて積極的な民生部品の活用と小型軽量化に最適な技術の導入が不可欠である.本稿では,PROCYON通信系構成,並びに,各コンポーネントの詳細を紹介する.

This research proposes an X-band high efficiency onboard SSPA (solid-state power amplifier) for deep space missions by focusing on GaN (gallium nitride) HEMT (high electron mobility transistor) whose remarkable material properties, such as high thermal conductivity, wide band gap, and high breakdown voltage, are suitable for high power and high efficiency applications. Developing a high efficiency onboard SSPA is one of the great issues when we consider some missions toward Mars, Jupiter, and much farther planets because of the requirements of both ultra-long distance communication and low power consumption. As a first step toward developing a SSPA for deep space, a breadboard model is fabricated based on preliminary design. It consists of a buffer amplifier, a driver amplifier unit, a high power amplifier unit, an automatic level control unit, a variable attenuator, DC/DC convertors, and an over current protection unit. Here, GaN HEMT is used in both driver amplifier and high power amplifier units. RF (radio frequency) characteristics of these amplifier units are evaluated in experiments. The driver amplifier unit achieves output power of 31.5 dBm with power gain of 33.5 dB and less than -26 dBc of IM3 (third order intermodulation distortion) at P1dB (1dB compression point) at 8.425 GHz. Moreover, the maximum efficiency is up to 35.2%. On the other hand, the high power amplifier unit achieves 42.3 dBm of output power with 46.1% of PAE (power added efficiency) at P3dB (3dB compression point) at 8.40 GHz. In addition, the integrated GaN SSPA bread board model achieves the maximum output power of 41.9 dBm and the maximum total efficiency of 31.0% at 8.40 GHz. At least more than 5% total efficiency improvement can be seen compared to the previous onboard SSPAs. Moreover, space applicability of GaAs (gallium arsenide) MMIC (monolithic microwave integrated circuit), GaN HEMT and DC/DC convertor that are expected to be used in the SSPA are confirmed in total ionizing dose test.

Ka-band communications is one of the most important technologies for increasing the amount of data acquired in deep space missions. As a first step toward developing this technology, a Ka-band extender was attached to an existing X-band transponder. The Ka-band extender can generate Ka-band signals from the transponder's signals. The extender is designed so as to reuse design elements of the X-band transponder. This approach ensures reliability of the extender without additional qualification, lowers production costs, and allows for flexibility in the Ka-band extender configuration. For instance, the minimum configuration is a simple upconverter, which is realized by sharing circuits to the greatest extent possible with the transponder. The extender is compatible with the Ka-band specifications in Consultative Committee for Space Data Systems standards. Properties such as a flexible coherent ratio, high-speed analog and digital modulation, and ultralow phase noise for radio science missions are provided. Here, a breadboard model of the Ka-band extender was evaluated in experiments. The Allan variance of the Ka-band output signal was less than 1 × 10^-12 (at 1 s), 1 × 10^-13 (at 10 s), and 1 × 10^-14 (at >100 s) when an external reference signal was used. The Allan variance degradation and phase noise degradation, which were caused by the internal phase locked loop or frequency translation loop, were also measured. The measured phase noise degradation was about 25 dB from the theoretical value.

技術の進歩と共に小型衛星に求められるミッション要求は高度化し,衛星は軽量化,低コスト化が求められている.カテゴリ-Aに属する月周回,ハロー軌道,ラグランジュ点などミッションでもより高性能な通信機器が要求されている.本研究では,カテゴリ-Aミッションの小型衛星に向けた,Sバンドトランスポンダを開発している.重量約1kg,寸法110×110×90mm^3,消費電力10w以下,ラグランジュ点でトランスポンダの検波を維持する.本開発により,カテゴリ-Aミッションの小型衛星設計に重要な役割を与える.本稿では開発している月・ラグランジュ点ミッションに向けた小型Sバンドトランスポンダを報告する.

衛星サブシステムのレイアウト自由度の拡大や信号ケーブル質量の軽減と超高速バス接続の両立を実現するために,信号ケーブルの一部を無線化することを提案する.無線システムを衛星構体内部という多くの障害物を含む閉鎖空間に適用するために,超広帯域無線伝搬技術(UWB)を用いることを提案する.UWBは,比帯域幅20%以上取ることで,多重波フェージングを克服することができる.そのため,狭帯域伝送に比べ有利と考えられる.UWBを衛星構体内へ適用するためには,その電波伝搬特性を明らかにする必要がある.小型科学衛星の機械環境試験モデルと,それを模擬した内部空間を用意し,電波伝搬特性を測定した.UWBモノポールアンテナとベクトルネットワークアナライザを使用し,3.1〜10.6GHzの周波数応答からパス利得の空間分布,遅延プロファイル,遅延スプレッドを測定した.その結果,狭帯域伝搬では深いフェージングの落ち込みであるデットスポットが生じ,UWBではこれらが発生しないことが分かった.また,伝送品質の向上を図るため,遅延スプレッドの制御を試みた.結果,電波吸収体による遅延スプレッドの制御が可能であることが分かった.