“Bottom line: Testing this tech will be helpful for navigation in contested environments where GPS may be degraded or denied,” said General Chance Saltzman, US Space Force chief of space operations, as the X-37B gears up for its eighth flight. Beyond the shroud of secrecy that has long enveloped the X-37B, this next flight marks a new age of transparency and technological aspirations for America’s reusable spaceplane.
The X-37B, a small, unmanned vehicle that looks like a miniaturized Space Shuttle, has already logged over 3,000 days in orbit across its previous missions. The program’s most recent venture, OTV-8, will demonstrate three developments at the cutting edge of aerospace engineering: high-bandwidth inter-satellite laser communication, the first in-space flight test of a quantum inertial sensor, and an augmented experimental capability made possible by a removable service module.
At the center of the mission is a demonstration of laser-based inter-satellite communications, technology a technology that will fundamentally change data transport in space. As General Saltzman put it, “OTV-8’s laser communications demonstration will mark an important step in the US Space Force’s ability to leverage commercial space networks as part of proliferated, diversified, and redundant space architectures.” What’s not just important but critical is not speed although laser links can provide orders of magnitude higher bandwidth than traditional radio-frequency system but resilience. By allowing satellites to talk directly to each other through tightly concentrated optical beams, the network is less vulnerable to jamming and eavesdropping, a key factor in both military and commercial constellations flying in increasingly congested low Earth orbit. But the engineering requirements are daunting: keeping track of highly moving satellites with great accuracy, correcting for atmospheric distortions over ground links, and achieving solid performance in the extreme thermal and radiation environment of space all require state-of-the-art optical and control systems.
Even more revolutionary is the X-37B as a vehicle for testing quantum navigation. The mission will transport what the Space Force calls the “highest-performing quantum inertial sensor ever tested in space.” These atom interferometers, which rely on the wave behavior of ultracold atoms, utilize the wave-like behavior of ultracold atoms to sense acceleration and rotation with unbelievable accuracy. According to Jonathan Kwolek, Ph.D., of the U.S. Naval Research Laboratory, stated, “By operating with cold, continuous atoms, we have opened the door to a number of advantages as well as novel measurement techniques. Ultimately, we would like to use this technology to improve inertial navigation systems, thus reducing our reliance on GPS.” Atom interferometers in practice detect infinitesimal motion changes by separating and recombining matter waves, with phase changes showing inertial forces. In contrast to traditional gyroscopes and accelerometers, quantum sensors are much less susceptible to long-term drift, promising autonomous navigation over long periods without external signals a feature of incalculable utility in GPS-denied environments, from lunar orbit to contested terrestrial battle spaces. But these sensors have challenges: today’s devices tend to run at low bandwidth, need ultrahigh vacuum chambers, and are environmentally noisy. Recent developments in miniaturization and hybridization with traditional IMUs are now overcoming these limitations, paving the way for their use outside the laboratory.
The mission flexibility of the X-37B is also boosted by its detachable service module, an innovation first seen in recent missions. This module increases the vehicle’s ability to support experiments from the Air Force Research Laboratory and the Defense Innovation Unit, with a versatile platform that allows for technology demonstration at a very quick pace. As Boeing’s senior vice president of space and launch, Jim Chilton, explained, “It’s a reusable spacecraft. It is autonomous, it flies without crew. It can be rapidly reconfigured to host a wide variety of experiments, and it can take off from standard launch pads on standard rockets under fairing, and it can land autonomously through public airspace.” The service module architecture not only enhances the payload capacity but also enables the incorporation of specialized hardware like the quantum sensor’s ultrahigh vacuum system or the optical terminals for laser communication without extensive redesigns of the primary spaceplane.
The X-37B’s engineering lineage is itself a witness to the history of reusable spaceflight. toughened uni-piece fibrous reinforced oxidation-resistant composite thermal protection system extends the tradition of the Space Shuttle but uses more robust and water-resistant materials. The autonomy of the vehicle, from its maiden flight on top of a Falcon 9 rocket to landing on a runway, is supported by sophisticated guidance, navigation, and control systems technologies now being extended even further by the quantum and laser research it conducts.
As the X-37B waits on the pad, it represents a convergence of aspirations: to protect communications in space, to steer without depending on vulnerable satellites, and to speed up the experimentation cycle in space. Each flight, gradually less secretive, provides a snapshot of future military and business space operations where quantum physics and photonics will perhaps become as vital as rockets and reentry tiles.
