The Research and Development Directorate has been promoting the downsizing and weight reduction of bus equipment (necessary for the basic functions and operation of artificial satellites, including those for power supply, orbit control and communication). Presently, the battery charger (GaN_BCR), which is one of the research targets of the Directorate, is mounted on the RApid Innovative payload demonstration SatellitE-2 (RAISE-2) for an in-orbit demonstration experiment. About the development, IWASA Minoru, developer of the battery charger, says as follows:

"The newly developed GaN_BCR will be used for the power control unit (PCU) of an artificial satellite. A PCU is a equipment to control power generation by solar cells and battery charge and discharge. The device adjusts the flow of electricity through switching control. For GaN_BCR, we increased the switching speed by several to 10 times relative to a conventional device for ripple control at the time of switching. As a result, we were able to reduce the number of components used to suppress ripple, which could cause damage to the equipment, thereby contributing to the downsizing of a PCU."

"In the R&D process, we strived to reduce invisible electromagnetic waves (noise)," says IWASA. Increasing the switching speed causes noise, which could also damage the equipment. In response, they identified the source of noise in an EMC test (conducted to comply with the noise regulations) and implemented countermeasures repeatedly. They also faced a challenge of dealing with the heat generated due to high-speed switching in vacuum space.

"We carried out the testing with a sense of tension as it is impossible for us to repair the device after the launch of the satellite on which it is mounted."

This fiscal year, they started to develop the technologies for small satellite PCUs, aiming to make practical use of the technologies in several years. If they achieve this, the PCU model will be changed for the first time in about 10 years. Downsizing a PCU means that more devices can be mounted for each space mission. Or if the power capacity is increased without changing the size of a PCU, it could contribute to the diversification of space missions.

"This is my 15th year at JAXA, and I feel very glad to be able to take on the challenge of carrying out an in-orbit demonstration experiment for the first time. I would like to succeed in the demonstration test on RAISE-2 first and eventually mount the battery charger on a larger satellite to make contributions to a wider range of space missions."