US Space Force completes second hosted sensor launch on Japanese satellite

The U.S. Space Force has finished deploying two space-surveillance sensors aboard Japanese navigation satellites, strengthening its ability to monitor objects in geosynchronous orbit through a bilateral initiative that places American military payloads on allied spacecraft and launch vehicles.

The second sensor lifted off Aug. 10 on Japan's H3 rocket as part of Quasi-Zenith Satellite 7, completing the Quasi-Zenith Satellite System-Hosted Payload program, known as QZSS-HP. The partnership stems from a 2020 agreement between the United States and Japan on national security space cooperation.

The U.S.-owned space domain awareness payload was designed and built by MIT's Lincoln Laboratory. According to the Space Systems Command, integration and testing with the Japanese host satellite took two years before the launch. The command announced the milestone Aug. 14.

With QZS-7 now in orbit, the American sensor will be operated by Mission Delta 2, the Space Force unit responsible for space domain awareness. The instrument sits in geosynchronous orbit over the Indo-Pacific region. Its observations feed in near real time into the U.S. Space Surveillance Network, the military's system of sensors used to detect, track and characterize satellites and other objects circling the Earth.

Col. Gina Peterson, deputy commander of Mission Delta 2 — Space Domain Awareness, said in a statement that QZSS-HP plays a key role in addressing threats from peer adversaries in space and in building resilient capabilities to detect, understand and maintain custody of objects in deep space.

The program is part of a broader U.S. strategy to diversify its space-based sensing architecture by leveraging allied infrastructure. Hosting military payloads on partner satellites reduces the need for dedicated American spacecraft and can complicate an adversary's targeting calculus, since the sensors are integrated into systems operated by allied governments.

The first QZSS-HP sensor was launched earlier on a previous satellite in the Quasi-Zenith constellation, which provides positioning, navigation and timing services for Japan and the wider Asia-Pacific region. The constellation is designed to complement GPS with improved coverage in urban canyons and mountainous terrain, where signals from standard orbit satellites can be blocked.

By placing the second sensor in geosynchronous orbit, the Space Force gains a persistent vantage point for tracking objects in one of the most valuable orbital regimes, home to many large communications and early-warning satellites. Maintaining custody of these objects is considered critical for protecting allied space assets and avoiding collisions.

The completion of the QZSS-HP program comes as the U.S. military continues to expand partnerships with allies in the space domain, including agreements with Australia, the United Kingdom and other nations to share data and host sensors on each other's systems.