Exploring New Technological Frontiers with Stratospheric Motors


The Pioneer Confronting the Uncharted Frontier

SoftBank is working on the research and development of the aircraft with the aim of early realization of High Altitude Platform Station (HAPS). HAPS converts solar energy into propulsive power using motors, allowing it to fly continuously for extended periods. However, as no motors which have the performance required by HAPS in the stratospheric environment existed, SoftBank’s challenge of developing such motors has begun.

Challenge to the Stratosphere

The toughest condition for HAPS, which flies in the stratosphere for an extended period, is the winter solstice in the northern hemisphere. HAPS uses weak and short sunshine during the day to generate electricity and stores it in batteries. Then, the stored electricity is used to continue flying during the longest night of the year. During the day-night cycle, motors constantly rotate, so the most important requirement for the motor is to be highly efficient in converting a small amount of electricity into propulsive power.

Furthermore, it is known that the environment in the stratosphere around 20 kilometers altitude where HAPS operates, generally has a temperature below minus 55°C and a pressure of approximately 70 hPa. While the low-temperature stratosphere may seem advantageous for motors due to the heat generated during rotation, our research has discovered cases where the temperature can drop to minus 85°C requiring exceptional reliability to withstand significant heat changes. Additionally, the weight of the aircraft needs to be significantly reduced by maximizing airflow in order to cool the motors, which is an essential aspect of HAPS. However, the stratospheric pressure results in low airflow rates, requiring further modifications to the cooling system for optimal efficiency.

A location that recorded ultra-low temperatures below minus 85°C(From flight logs spanning 1.91 million hours by Loon Inc.)

Future Possibilities Brought by Innovative Motor Technology

When a lightweight, highly efficient, and high-performance motor that can practically withstand the harsh stratospheric environment and work continuously for an extended period is developed, it will facilitate the establishment of communication networks in areas that require HAPS, such as regions lacking networks and during disaster events. With approximately half of the world's power consumption attributed to motor power, the spread of technologies developed via this motor can contribute to the realization of a sustainable society.

Progress in Research and Development

SoftBank's Research Institute of Advanced Technology and Nidec's Product Technology R&D Center jointly developed a light-weight, high-efficiency, and high-reliability axial flux-type motor for HAPS. (Press Release)

This axial flux-type motor realizes small, light weight and high torque by maximizing magnetic field strength through the optimized magnet arrangement. The motor is also designed to enhance reliability by encapsulated magnets in a rotor and to keep stable performance in the stratosphere’s hypobaric environment by giving the motor high thermal dissipation.

Axial flux-type motor(Provided by Nidec Corporation)

HAPS Motor

Going forward, SoftBank will continue to conduct research and development for the early realization of HAPS, such as securing reliability that enables long-term flight for several months, responding to certification for the aviation industry, along with investigating and understanding the stratospheric environment.

Research Areas