Tests in Japan have shown successful data connection with an autonomous high altitude platform station (HAPS) flying at an altitude of 20km for the first time, writes Nick Flaherty. The trial with Space Compass and NTT DOCOMO connected a 4G LTE base station on the ground with the HAPS at 38 GHz then down to smartphones on the ground in Kenya. The downlink used the S band at 2 GHz that can be received by mobile phones and covered an area with a diameter of 100 km to 200 km. The HAPS system is the Zephyr (see issue 53), which is designed, manufactured and operated by AALTO HAPS, a subsidiary of Airbus Defence and Space. The LTE base station was connected to the ground gateway station, and a non-regenerative relay reflected the radio waves through the communication device mounted on the HAPS flying in the stratosphere, connecting to the 4G device on the ground. This showed a throughput of more than Underwater vehicles have to manage a complex environment of currents, fighting against many flows as they attempt to stay on course, writes Nick Flaherty. Peter Gunnarson and John Dabiri at the California Institute of Technology have designed an underwater robot that makes use of these currents to cut down on the energy needed to travel, “surfing” vortices to make its way to its destination. The project used the Caltech Autonomous Reinforcement Learning (CARL) robot equipped with an onboard inertial measurement unit, ten motors to allow movement in all three axes, and a simple but effective algorithm. plan to launch a commercial service using the Zephyr HAPS in 2026 to provide mobile phone and data coverage in disaster areas as the Zephyr can stay in the air for over two months in trials. Space Compass and NTT DOCOMO are also developing a second connection from the HAPS up to satellites in low earth orbit as part of the radio access network to provide even wider access. The success suggests that a similar technique could be used to allow autonomous vehicles to improve their efficiencies significantly by interacting with background flows. Data links Underwater vehicles Data transmission test on a high Surfing underwater currents to reduce power 4.66 Mbit/s during reception of the radio wave transmitted from the ground gateway station to the 4G device via HAPS. The technology to stabilize the beam to provide the connectivity coverage at a certain position toward a fixed point on the ground from the HAPS rotating in the stratosphere was implemented. Space Compass and NTT DOCOMO If the magnitude of the acceleration in the crossflow-direction exceeded a threshold, CARL would swim in the same direction as the acceleration. The robot was tested in a 1.5 m deep and 5 m long tank, where vortex rings were generated by pulsing a wall-mounted thruster. Using the algorithm, CARL was able to surf the length of the tank using onefifth of the energy as a robot without the same programming. The linear acceleration as sensed by the onboard IMU was found to correspond with the pressure gradient of the background flow, and rotational acceleration is suggested as a method for measuring the vorticity of the vortex ring. An autonomous UAV has relayed mobile phone calls for the first time (Image courtesy of NTT DOCOMO) The trajectory of CARL shown by the white line, surfing vortices (Image courtesy of John O. Dabiri and Peter Gunnarson) Platform one 14 April/May 2025 | Uncrewed Systems Technology
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