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The Forefront of Space Science

Development of Next Generation X-band Digital Transponder
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Toward next-generation observation

The project to develop the new transponder began in FY2000. In two years by FY2002, the demonstration experiments for the new functions stated above had been completed. For three and half years from FY2003, we will produce the prototype to validate its flightworthiness. It will be built based on the trial model used for the demonstration experiments. Probably, by that time this article will appear on the web, we will complete selection of components eligible for use on explorer, determination of interface with other onboard equipment and adaptation to onboard product specification of digital signal processing circuit, and be on the way to select the target investigating the future planetary exploration projects. The prototype development of the base band section including digital signal processing has been completed and, hereafter, we will proceed with the development of high frequency, frequency synthesis, and power supply sections. The difference from the trial model for functional evaluation is change of components to those suitable for space use and review of interface specification with other equipment. Also, we have decided to change the configuration from four stages of the trial model to five stages. As for other differences, please refer to Table 1, which compares the three models, the HAYABUSA¡s transponder, trial model and prototype. Our development is being smoothly undertaken.

When will our transponder make a debut? Go to Venus, or Mercury? Anyway, we hope that our transponder will be boarded on the first deep space explorer for the newly organized Japan Aerospace Exploration Agency (JAXA). For now, language from explorers sounds like the gentle and soft Buddhist invocation. By the IT technology remarkably advancing year by year, in the future the Zen riddle may be exchanged with explorers far away in space. Space science has a great power to shake the human¡s view of the world. If language from explorers is to convey us the view of the world, how profound the deep space communication is!

Table 1 Comparison of X-band Transponders
  Prototype Model X-band transponder for HAYABUSA Trail Model for functional evaluation
Transceiver Receiver (estimate) Transmitter Transceiver
Dimension (mm) 150 x 150 x 120 190 x 160 x 103 68 x 143 x 90 150 x 150 x 94.5
Weight (g) 2100 2250 1510 3400
Density (g/cm3) 0.78 0.72 0.70 1.60
Power Consumption
18.2 17 9.6 x 11 19.8
Function Modulation index variable Regenerative ranging function Stabilized power supply Modulation index variable Stabilized power supply Modulation index variable Signal regeneration type ranging function Unstabilized power supply
(Specific gravity: 1.74)
(Specific gravity: 1.74)
(Specific gravity: 2.69)
* Configuration of the transponder under development is one box type by combining transmitter and receiver.
The receiver of the HAYABUSA¡s X-band transponder consists of two boxes. Function of receiver is covered by two, providing redundancy function (configuration).

(Tomoaki Toda)

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