A US military grade JLENS balloon. Photo: Twitter / Missile Threat

In a throwback to 19th-century aerial warfare, the US is mulling the use of hot-air balloons for hypersonic missile tracking and aerial surveillance.

Politico reported that high-altitude inflatables flying at 60,000 to 90,000 feet could supplement America’s extensive satellite surveillance network and be used to track hypersonic weapons amid growing US concerns about China and Russia’s growing arsenals of the weapon. 

Pentagon documents cited in the report show that the technology is moving from the US Department of Defense’s (DoD) scientific community to the US military. 

Budget documents from the last two years show that the Pentagon has spent US$3.8 million on balloon projects, with plans to spend $27.1 million in the fiscal year 2023, marking a slightly more than sevenfold increase in spending for high-altitude surveillance balloons.

In terms of specific systems, the Politico report identifies the Covert Long-Dwell Stratospheric Architecture (COLD STAR) as the balloon program that has just been transferred to the US military. However, it also notes that specific details are unavailable due to the project’s classified nature. 

According to Tom Karako, a senior fellow with the Center for International and Strategic Studies (CSIS), a Washington-based think tank, “high or very high-altitude platforms have a lot of benefit for their endurance on station, maneuverability and flexibility for multiple payloads,” as quoted by Politico.

In terms of missile defense, the balloons combine the persistent presence delivered by terrestrial sensors, the wide-area coverage of airborne sensors, and the look-down angle to spot incoming cruise missiles, notes defense publication Tactical Defense Media.

While terrestrial sensors have been the backbone of missile defense since the Cold War, CSIS says they suffer from various inherent limitations.

For example, the Earth’s curvature limits their effectiveness against low-flying threats such as cruise missiles, they have a limited number due to size and cost, their fixed location and significant energy emissions make them potential targets and the loss of one terrestrial station could result in a massive gap in sensor coverage. 

In contrast, CSIS notes that balloon-based sensors can detect missile threats at greater ranges compared to terrestrial ones, elevated platforms can carry multiple types of sensors, and they may be more survivable than terrestrial sensors as operators could field them in larger numbers. 

These balloons also have a fraction of the cost of satellites. Military Review mentions that one high-altitude balloon has an estimated initial development and operating cost of $100,000 compared to $1.6 billion for one infrared satellite. 

However, CSIS also mentions drawbacks for balloon-based sensors, including the need for a more robust and resilient network architecture and reduced sensor fidelity due to size, weight and power limitations.

The Pentagon is transitioning high-altitude balloon projects to the military services. Image: Screengrab

In addition, the US Congressional Research Service (CRS) mentions the potential vulnerability of such balloons to weather and ground fire. The source states that many US and foreign surveillance balloons have been lost in adverse weather, and there are mixed opinions about their vulnerability to enemy fire. 

On the one hand, proponents say that such balloons are survivable due to their low radar cross-section (RCS) and can sustain several hits before losing altitude. On the other hand, opponents say they are big targets within the range of several enemy weapons. 

Popular Mechanics describes COLD STAR as a balloon that can operate undetected in enemy airspace, featuring autonomous navigation, high fidelity sensors and onboard AI. In addition, the source says that COLD STAR’s balloon is transparent to radar while its gondola can feature stealth shaping by eliminating straight lines and corners that generate strong radar returns. 

In a Politico interview, Russell Van Der Werff, engineering director at Raven Aerostar, which manufactures the COLD STAR balloons, said each balloon consists of a flight control unit powered by batteries charged by renewable solar panels. They also have a payload electronics package for flight safety, navigation and communications. 

Another system that may be under consideration is the Joint Land Attack Cruise Missile Elevated Netted Sensor System (JLENS), which the US DoD describes as featuring advanced sensor and networking technologies to provide persistent, 360-degree, wide-area and precision tracking of land-attack cruise missiles and other air-breathing threats. It consists of a fire control radar system and a wide-area surveillance system. 

Each radar system uses a 74-meter tethered balloon, mobile mooring station, radar and communications payload, processing station and associated ground equipment. 

The systems can work together or independently and are transportable by road, rail, sea and air. In addition, the JLENS can be integrated with SM-6 and Patriot missile interceptors, as noted in Missile Threat. 

However, the source reports that during an October 2015 test, the JLENS fire control balloon broke from its tethers due to a failure in its automatic deflation device and high winds, resulting in the balloon floating over rural Pennsylvania, eventually landing in Moreland Township. 

As a result, Politico notes that the US Army decided to drop the JLENS project after spending $2 billion in development costs.