Tomoaki Toda

We will discuss wireless technologies with emphasis on spacecraft proximity links. The proximity in space covers a link distance from several meters to thousands kilometers. Various telecommunication schemes have been designed for and applied to spacecraft for the proximity links. Those wireless links usually offers line-of-sight ranging and velocity measurement capability, too. It is important to know that their specification is not simply determined by themselves. Within strict constraints on onboard resource allocations like mass, power, and dimensions, the systematic point of view considering a total spacecraft system is also necessary. We will introduce SCOPE mission in this paper, as an example to take a look at the process of such a systematic optimization. It will help you to understand a mission-oriented development of space technologies. In recent years, in addition to inter-spacecraft wireless technologies, intra-spacecraft ones have been within a scope of practical applications. We will also discuss them to remove wire harness within a spacecraft, especially on their purpose and effectiveness, and their future applications.

Dual (X and Ka) band downlink operation is demanded scientific satellite missions, to facilitate much higher data rate and to increase the available radio channels. A combinations of a corrugated horn (for X band) and a disk-on-rod antenna (for Ka band) have used as a primary feed for a satellite-borne dual-band reflector antenna, but its volume was not satisfactorily small. The anothers proposed a combination of a sequential four-element array of rectangular microstrip antennas fed with L-shape probes for X band and a four-element array of helical antennas for Ka-band, to realize a small-volume, light-weight circular-polarized primary radiator. This paper reports the performances-VSWR, XPD, and radiation patterns of a prototype radiator.

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.

Japanese deep space missions have been developed based on Usuda Deep Space Center 64m station (UDSC64). Thus, it is the onboard telecommunication subsystem that determines deep space link capabilities of Japanese deep space spacecraft. Beginning by introducing the current performance of Japanese deep space telecommunications based on our Venus mission, AKATSUKI, we will briefly review those of our past deep space missions by comparing them with ones of NASA. Finally, we will discuss the technologies under development for our future missions and the future prospects of Japanese deep space telecommunications.

PLANET-C (PLC) is the mission of Japan Aerospace Exploration Agency (JAXA) for Venus exploration. It is a successor of HAYABUSA in the history of Japanese deep space missions and is expected to be the first Japanese planetary orbiter. The spacecraft will be launched in the summer of 2010 from Tanegashima Space Center. The mission has demanded new onboard telecommunication instruments. Among them are X-band digital transponder, high gain flat antenna, and low gain wider field of view antenna. Through their developments, new technologies such as deep space regenerative ranging adapted for JAXA ground stations have been successfully incorporated into the PLC system. They are now raedy for their first space-borne demonstration. We will discuss these telecommunication technologies newly introduced for the PLC mission.