Toward the Early Realization of Flying Base Stations “HAPS”



Currently, as the number of high-performance IoT devices increase in addition to smartphones and tablets, efforts are being made to promote the spread of 5G networks to achieve a wider range of Internet connectivity. On the other hand, there are still many regions across the globe that have poor connectivity, where no Internet connection is available or the connection is unstable.

The causes of this poor connectivity include geographical restrictions that hamper the installation of ground base stations, as well as the limited capacity of satellite communications.

In order to solve these problems, SoftBank has set its focus on the stratosphere, which is at an altitude of about 20 km, higher than the altitude at which commercial jet planes fly. We are conducting R&D on HAPS (High-Altitude Platform Station, a flying base station designed to remain stationary in the stratosphere.

What is HAPS?

HAPS are flying objects that continue to fly in the stratosphere over a long period of time. Ideally, they depend solely on solar power for their energy sources. In addition, HAPS that are mounted with communications equipment are positioned as one of “Non-Terrestrial Networks (NTN)”, which are aimed at the realization of “Beyond 5G/6G”, the next-generation of mobile communication systems after 5G, which is currently in use.

  • Flying object: An artificial object that flies at high altitudes

There are two types of HAPS. One is the “Lighter-than-Air (LTA)” type, which maintains its flight using buoyancy such as balloons and airships. The other is the “Heavier-than-Air (HTA)” type, which stays in the air using aerodynamic lift in the same manner as an airplane.

Project Loon, which used balloons, a form of LTA HAPS, achieved a fleet of HAPS vehicles by enabling altitude control by leveraging AI forecasts.

  • Project Loon: A project undertaken by Loon, a subsidiary of Google’s parent company, Alphabet. They provided communications to the ground using network equipment installed on balloons floating in the stratosphere. Loon was discontinued in January 2021. Since then, Loon’s rich knowledge has been passed on to SoftBank, including our acquisition of approximately 200 patents relating to HAPS technology that were held by Loon.

However, LTA HAPS has the disadvantage of not being suited for year-round operations, due to problems such as the possibility of being carried away by strong seasonal winds.

On the other hand, HTA HAPS maintains sufficient speed during its flight, and thereby flies in a stationary rotation without being carried away by the wind. By flying HAPS in the skies above remote islands and mountainous areas where it was previously impossible to install base stations, connectivity can become available in a broader range of areas.

Setting its focus on the advantages of HTA HAPS, SoftBank has been developing HTA HAPS while utilizing the expertise that it inherited from Loon.

Research and Development

SoftBank began its HAPS project in 2017 and has developed a prototype aircraft (the “Sunglider”) in cooperation with AeroVironment, Inc.

Subsequently, test flights were carried out at the NASA Armstrong Flight Research Center (AFRC). In September 2020 at Spaceport America, Sunglider succeeded in a stratospheric test flight and the delivery of LTE connectivity from the stratosphere.

This test flight successfully demonstrated that there is sufficient potential for communication systems that operate from the stratosphere. On the other hand, it also brought to light the requirements necessary for commercialization, including reductions in the weight of the airframe and improvements in the performance of the motor. We are currently working on the development of a successor aircraft based on these findings.

Energy Required to Power HTA HAPS

HTA HAPS is equipped with solar panels that generate energy from the sun to power the propellers, and gain aerodynamic lift as they move through the atmosphere.

Due to the large amount of energy necessary for flight, realization of HTA HAPS is said to be more difficult in comparison to LTA HAPS, which remains aloft using the buoyancy of helium gas.

In order to solve this problem, the energy efficiency of the aircraft needs to be improved. Specifically, a large aircraft with long and lightweight wings that can attach many solar panels is advantageous, and a tailless aircraft, which has low air resistance, is considered to be the ideal shape.

HAPS in this shape were actively developed by NASA in the 1980s. Stratospheric flight tests were then carried out for a series of aircrafts. In Japan in 2002, NICT (National Institute of Information and Communications Technology) rented an aircraft from NASA and carried out a CDMA communications verification test for mobile devices.

The diagram shown above illustrates the energy balance of HAPS as a communication base station. HAPS consumes a certain amount of energy required for flight and for the provision of communication services. In the stratosphere where there is no obstruction by the clouds, energy can be reliably obtained from solar power.

On the other hand, it cannot obtain solar energy during the night so energy required for night time has to be charged during the day. The red line in the graph indicates the charging rate, which reaches 100% at sunset, then starts to decline through the night. If the energy can be sustained until sunlight is received on the next day, continuous flight and the provision of uninterrupted communication services can be achieved.

HTA HAPS has reached a level at which the above-described energy balance can be achieved as a single aircraft, regardless of its size. However, to use an aircraft with the performance necessary for commercialization, further improvements such as reducing the weight of the aircraft and enhancements in energy efficiency must be made.

Cooperation with Aircraft Manufacturers and Regulators

Taking a look at HAPS initiatives around the world, Airbus has developed a smaller-sized HAPS called “Zephyr,” which achieved the world’s longest flight record of 64 days (as of August 2022). There are also a number of companies that are engaged in research towards the realization of advanced technologies such as “environmentally-friendly advanced unmanned aerial vehicle (UAV)” equipped with jet engines, as well as fuel cell-powered aircraft.

In addition to the advancement of technologies, resolving regulation issues related to operations is also crucial for the commercialization of HAPS.

There is no precedent in the history of aviation for unmanned aircrafts that fly in the stratosphere for extended periods of time. Through the HAPS Alliance, which brings together aircraft manufacturers and other stakeholders, we are engaging in dialogues and working with regulators in various countries, including the promotion of our HAPS concept and its safety to the Federal Aviation Administration (FAA), which sets global safety standards.

We will continue to work towards the early realization of HAPS services by conducting research and development of the aircraft, as well as working towards the establishment of rules for the stratosphere.

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