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upstart writes:

The X-37B spaceplane is flying missions few would have foreseen when the program began:

The US military's reusable winged spaceship rocketed back into orbit Thursday night [August 21, 2025] atop a SpaceX rocket, kicking off a mission that will, among other things, demonstrate how future spacecraft can navigate without relying on GPS signals.

The core of the navigation experiment is what the Space Force calls the "world's highest performing quantum inertial sensor ever used in space."

This is one of many payloads mounted on the military's X-37B spaceplane when it lifted off aboard a Falcon 9 rocket from Kennedy Space Center in Florida at 11:50 pm EDT Thursday (03:50 UTC Friday).

[...] Military leaders tout the X-37B's purpose as a technological testbed that can ferry experiments from Earth to space and back. Many of the spaceplane's payloads have been classified, but officials typically identify a handful of unclassified experiments flying on each X-37B mission. Past X-37B missions have also deployed small satellites into orbit before returning to Earth for a runway landing at Kennedy Space Center, Florida, or Vandenberg Space Force Base, California.

On this mission, the Space Force says the X-37B carries instrumentation to demonstrate quantum navigation, and a laser inter-satellite relay terminal to allow the spaceplane to connect with other spacecraft in orbit.

The quantum sensor package will "inform accurate unaided navigation in space by detecting rotation and acceleration of atoms without reliance on satellite networks like traditional GPS," the Space Force said in a statement before the launch.

[...] Recognizing the importance of GPS signals, the Space Force said the quantum sensor experiment on the X-37B spaceplane will test technology useful for navigation in "GPS-denied environments." Quantum navigation could also help spacecraft navigate in deep space, around the Moon or other planets, where missions can't count on receiving GPS signals.

[...] The Pentagon's twin X-37Bs have logged more than 4,200 days in orbit, equivalent to about 11-and-a-half years. The spaceplanes have flown in secrecy for nearly all of that time.

The most recent flight, Mission 7, ended in March with a runway landing at Vandenberg after a mission of more than 14 months that carried the spaceplane higher than ever before, all the way to an altitude approaching 25,000 miles (40,000 kilometers). The high-altitude elliptical orbit required a boost on a Falcon Heavy rocket.

In the final phase of the mission, ground controllers commanded the X-37B to gently dip into the atmosphere to demonstrate the spacecraft could use "aerobraking" maneuvers to bring its orbit closer to Earth in preparation for reentry.

Now, on Mission 8, the spaceplane heads back to low-Earth orbit hosting quantum navigation and laser communications experiments. Few people, if any, envisioned these kinds of missions flying on the X-37B when it first soared to space 15 years ago. At that time, quantum sensing was confined to the lab, and the first laser communication demonstrations in space were barely underway. SpaceX hadn't revealed its plans for the Falcon Heavy rocket, which the X-37B needed to get to its higher orbit on the last mission.

The laser communications experiments on this flight will involve optical inter-satellite links with "proliferated commercial satellite networks in low-Earth orbit," the Space Force said. This is likely a reference to SpaceX's Starlink or Starshield broadband satellites. Laser links enable faster transmission of data, while offering more security against eavesdropping or intercepts.

Gen. Chance Saltzman, the Space Force's chief of space operations, said in a statement that the laser communications experiment "will mark an important step in the US Space Force's ability to leverage proliferated space networks as part of a diversified and redundant space architectures. In so doing, it will strengthen the resilience, reliability, adaptability and data transport speeds of our satellite communications architecture."

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