World-first demonstration tracks high-altitude platform using ground laser pulses

SoftBank, Hitotsubashi University and Japan’s National Institute of Polar Research have demonstrated a way to track a high-altitude communications platform from the ground using laser pulses, marking a step toward future optical links between the ground, stratosphere and satellites.

The demonstration used a corner cube reflector (CCR) mounted on an LTA-type HAPS operated by U.S. company Sceye. A compact, portable laser-ranging system on the ground continuously tracked the HAPS and detected laser pulses reflected back from the reflector while the platform was operating in the stratosphere.

SoftBank describes the test as the world’s first demonstration of this specific form of ground-based laser ranging of a stratospheric HAPS, based on publicly available information reviewed by the three organizations through September 8, 2026.

Why bounce a laser off a HAPS?

The experiment may sound simpler than a conventional laser communications demonstration because the HAPS did not transmit data through an optical terminal. Instead, it carried a passive reflector.

A CCR is designed to send incoming light back toward its source, regardless of the angle at which the light enters. By putting one on the HAPS, researchers could test whether a ground station could continuously acquire and track a moving platform, direct a laser beam toward it, and detect the extremely weak return signal.

HAPS platforms operate around 20 kilometers above Earth, and their position and orientation constantly change. A communications system therefore needs to locate the aircraft, acquire it optically, keep a narrow laser beam pointed at it, and maintain tracking as it moves. SoftBank identifies this collection of functions as pointing, acquisition and tracking (PAT).

The CCR test allowed researchers to examine those challenges before installing a full optical communications terminal on the aircraft.

From laser ranging to optical communications

The demonstration took place on August 23 and 24, 2026, after an initial observation and software adjustment on August 22. The HAPS was operating over waters off Cape Muroto in Kochi Prefecture.

The ground system continuously acquired and tracked the HAPS while sending pulsed laser light toward its CCR and receiving the reflected signal. The experiment also generated data on how much the laser signal was attenuated while traveling between the ground and the stratosphere.

That atmospheric information could help determine the requirements for future HAPS optical communications equipment, including how terminals should be installed and operated. The test is also technically demanding because the reflected beam from a CCR returns within a very narrow angular range.

SoftBank says the pointing and receiving-tracking accuracy required for satellite laser ranging is roughly an order of magnitude higher than that used in conventional optical communication links.

Importantly, the laser used in the experiment was not high power, and the system was programmed to stop transmission whenever a crewed aircraft was detected in the direction of the HAPS.

How this differs from earlier experiments

The demonstration builds on previous work showing that optical communications can operate between the stratosphere and the ground.

In 2005, the German Aerospace Center’s STROPEX experiment demonstrated a 1.25 Gbit/s optical downlink from a stratospheric balloon at about 22 km altitude to a ground station.

The U.S. Navy’s Naval Information Warfare Center Pacific has also developed the Stratospheric Optical Link Demonstration (SOLD) as a high-altitude balloon experiment to reduce risk for optical communications technologies.

SoftBank’s approach was different. Rather than sending communications data between an optical terminal and the ground, it created a round-trip laser path: ground → HAPS → ground.

The next step is connecting with light

The CCR itself cannot transmit data. It is passive. A future communications system would need optical transceivers on the HAPS capable of transmitting and receiving laser signals while maintaining a link with ground stations or satellites.

SoftBank says the tracking system being developed for its optical communications terminal uses the same software architecture as the laser-ranging system, meaning experience from the latest demonstration can be carried into the next stage.

The company’s broader objective is a three-dimensional communications network in which HAPS platforms connect ground users with infrastructure and potentially LEO satellites, using optical links as high-capacity connections between different layers of the network. SoftBank is already testing HAPS communications services with Sceye, including smartphone connectivity, as it works toward potential commercialization from 2027 onward.

The latest demonstration addresses one of the fundamental problems such a network must solve. Reliably finding, tracking and maintaining a laser link with a moving platform 20 km above the ground.