抄録
The ranging link could be a bottleneck and constrain a mission design because it suffers from a degradation of its two-way propagation. JAXA has introduced an onboard ranging signal regeneration scheme to solve this problem. It is new in the point that we do not apply correlation processes to a detection of ranging codes to be regenerated, and that a signal improvement by integration processes alone contributes to the regeneration. We call this technology as synchronous integration. We have developed both an onboard instrument and ground equipment in parallel. The preliminary test using a breadboard model of the X-band transponder and a prototype of our future ground system successfully proved that our regenerative ranging was effective. Based on this result, this new ranging scheme was adopted for our Venus exploration mission, PLANET-C. PLANET-C was launched in May 2010. During her transfer orbit to Venus, the comparison test between the regenerative and transparent ranging was conducted. This was the world first achievement of the regenerative ranging based on the synchronous integration scheme. We gave a detailed analysis to this experimental result. Our regenerative ranging performs better than our transparent one when a received uplink ranging signal to noise power density ratio is worse than 60 dBHz. At the ratio less than 40 dBHz, the regenerative ranging still keeps functioning while the transparent one needs an extended integration time for its operation. Compared with our current transparent ranging, our regenerative ranging has a 14-dB recovery gain for the uplink. It enables us five times as long a ranging link distance as before.
