The future of 21st century air warfare conjures up images of hypersonic missiles, swarms of smart drones, directed-energy weapons and artificial intelligence. Balloons don’t immediately come to mind. But with the recent downing of a Chinese high-altitude surveillance balloon over the Atlantic Ocean, after it crossed the continental United States, we are reminded that what was once old is new again.

Just as the emergence of the submarine, the self-propelled torpedo, mines and aircraft during the early 20th century added subsurface and above-surface threats in the contest for sea control, so too do small drones, loitering munitions, missiles and, yes, balloons add threats to air control from above and below the altitudes of conventional air superiority.

To gain an asymmetric advantage, U.S. adversaries increasingly seek to operate at the edges of the air domain — that is, at altitudes below and above the “blue skies,” where high-end fighter and bombers typically fly. In the air littoral, located below 15,000 feet, adversaries can exploit a mix of old and new technologies — such as man-portable air defense systems, radar-guided anti-aircraft artillery, cruise missiles, dual-use drone technologies and loitering munitions — to keep the airspace contested.

The recent intrusion of a Chinese surveillance balloon into American airspace points to the potential emergence of an analogous set of littoral threats at the highest reaches of the air domain.

The space littoral

The Chinese balloon incident offers a first glimpse of the contest to control the “space littoral” — that is, the airspace at altitudes between about 60,000 feet (known as the Armstrong limit) and the edge of space, roughly 330,000 feet (or the Kármán line).

The use of high-altitude spy and military balloons is itself not new. The Japanese lofted incendiary balloons into the jet stream toward the West Coast in World War II. The United States conducted a series of spy balloon missions over the Soviet Union in the 1950s and even more recently tested the use of mass surveillance balloons across the United States.

What’s different today is that balloons guided by artificial intelligence can both cheaply access and persist in the space littoral, thanks to a combination of technological advancements and commercial processes. Commercial companies are increasingly accessing the space littoral, using high-altitude balloons for ultrahigh-resolution imagery, internet communications and scientific research. These dual-use space assets will increasingly place the capabilities to contest the space littoral in more adversaries’ hands.

Adversaries will seek to gain an advantage by operating in the zone of domain convergence between air and space. A 2018 article in the PLA Daily, the official newspaper of the Chinese People’s Liberation Army, called the space littoral a “new battlefield in modern warfare.” Though a Chinese spy balloon floating across the United States is not contesting air superiority — it is transiting airspace — the episode hints at other possibilities.

Beijing could use high-altitude balloons to launch missiles or swarms of drones against air bases and known radar sites. China seems to recognize these possibilities. “At present and for a long time to come, the vast majority of air defense weapons will not threaten targets in near space,” China’s Aerospace Security Strategic Concept concluded in 2016, characterizing the space littoral as “an important penetration channel for rapid and long-range strikes.”

But these are more than mere words. In 2018, the Chinese state media reported the test of a high-altitude balloon carrying hypersonic missiles.

Other Chinese military writings also demonstrate interest in these ideas. In 2020, two Chinese strategists argued that “near-space weapons have incomparable advantages over traditional weapons.” Owing to the advantage of height, they explained that the “reconnaissance field of view and strike coverage” area of high-altitude balloons is “much larger than that of traditional aircraft,” adding that “near space-weapons enable fast, agile, and stealthy ground strikes” and “its stealth ability is strong, so it is not easy to be detected and identified by radar, infrared and other detection equipment.”

Because these balloons have a very small radar cross section, which renders them harder to detect and eliminate, they could pose a persistent threat to airborne systems, including aircraft, operating in the blue skies below them.

Indeed, Gen. Glen VanHerck, the head of North American Aerospace Defense Command and U.S. Northern Command, has acknowledged the United States failed to detect previous incursions by Chinese spy balloons into American airspace, exposing a “domain awareness gap.” Last month, after NORAD expanded its filter for slow-flying objects, it started detecting more objects, leading to the shoot-down of three other objects later determined to have a “benign purpose,” having most likely been launched by private companies or research institutions. Even if detected, high-altitude balloons will still pose the challenge of filtering out actual threats from the background noise.

China also might employ balloons to detect and engage American air defense radars, effectively blinding the entire system. Chinese researchers have made the case for employing balloons to “induce and mobilize the enemy’s air defense system, providing the conditions for the implementation of electronic reconnaissance, assessment of air defense systems’ early warning detection and operational response capabilities.”

Even if the United States manages to intercept enemy balloons, they are cheap. The United States used a $250 million F-22 fighter armed with a $472,000 AIM-9 Sidewinder missile to shoot down a Chinese surveillance balloon that probably cost thousands of dollars. The exchange rate for the other three shoot-downs was likely even more unfavorable. If an adversary were to employ hundreds of these balloons, this approach would quickly become unsustainable.

In short, the Chinese balloon incident portends a future in which cheap, persistent capabilities will challenge aspects of U.S. air superiority.

A littoral paradigm

The U.S. Air Force needs to prepare for this future now. This calls for doctrinal innovation, not technological invention or incremental adaptations of existing weapon systems. New thinking, not technology or legacy ideas, is the answer.

The first step is to recognize and name the problem. Incorporating the concepts of the “air littoral” and “space littoral” into service and joint doctrine would help to build a common language around the problem the force wants to solve. The second step is to develop new operational concepts and vertical schemes of maneuver for operating in these zones.

The littorals are the messy middle area between sea and land, ground and sky, and air and space. The characteristic of domain convergence makes them simultaneously more challenging and more critical for military operations: They are the avenues of transit, paths of attack and waypoints of cross-domain maneuver. They are also now becoming areas of persistent contestation, whether the U.S. Air Force likes it or not.

U.S. Air Force Col. Maximilian Bremer is the director of the Special Programs Division at Air Mobility Command. Kelly Grieco is a senior fellow with the Reimagining U.S. Grand Strategy Program at the Stimson Center think tank and an adjunct associate professor of security studies at Georgetown University. This commentary does not necessarily reflect the views of the U.S. Defense Department nor the U.S. Air Force.

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