Chapter 23 - Telecommunication subsystem and newly introduced Ka-band performance of HAYABUSA2 asteroid sample return mission

Abstract

HAYABUSA2 is the first JAXA deep-space mission employing Ka-band. In spite of strict constraints inherited from the first HAYABUSA design, its update including the Ka-band function was completed. We report that the strictly restricted development is similar to that of small spacecraft. Our development style and the experiences in HAYABUSA2 are suitable for them. HAYABUSA2 stayed around the asteroid, Ryugu more than one year and successfully brought us Ka-band data in its proximity phase. From the analysis, we learned that Ka-band link was worth being implemented for our future missions. The data proves that Ka-band actually played an important role in the critical events of HAYABUSA2 in preparation for touch-down and sampling challenges. However, we also came to know that 7.6 times as many interruptions of Ka-band as that of X-band in the telemetry operations of HAYABUSA2 occurred. Therefore, our interest is now in making Ka-band operations more productive. We are proposing to unite Ka-band with X-band for the better use of Ka-band. In this proposal, we investigated the recovery of lost Ka-band data by X-band retransmission. With this method, we estimate that 2.8 times better data transfer than X-band only link is possible at the cost of 30% of X-band capability. Encouraged by HAYABUSA2 results, the demonstration of our X- and Ka-band hybrid repeat request scheme is underway by taking the opportunity of the JAXA Martian mission.