WASHINGTON — A new study released Dec. 18 sheds light on potential challenges in the Pentagon’s ambitious effort to deploy a network of space sensors for detecting and tracking hypersonic missiles. 

Based on internal modeling and simulation efforts, the study by the Center for Strategic and International Studies identifies areas for improvement in the planned network and raises questions intended to inform the conversation on what it takes to defeat these highly maneuverable missile threats.

“There is no such thing as a perfect sensor architecture design,” said the report titled “Getting on Track: Space and Airborne Sensors for Hypersonic Missile Defense.”

Hypersonic weapons fly at more than five times the speed of sound. Their speed and unpredictable flight paths make them difficult to detect and track. 

The study highlights Defense Department initiatives to build a multi-layer system of missile-tracking sensors and warns that more effort needs to be put into the technology used to stitch together sensor data — known as sensor fusion. This is critical to build accurate “tracks” and avoid confusion, the report said, as one missile traveling fast can look like several other objects.

DoD is investing billions of dollars in space sensors as the linchpin of a hypersonic defense architecture, and has “a lot of really smart people that are working on this problem,” said Thomas Karako, director of the CSIS Missile Defense Project. The report, he said, is an effort to broaden the conversation and warn of potential pitfalls. 

Technical challenges

While infrared and electro-optical sensing technologies are mature, hypersonic missile tracking is far more difficult than traditional ballistic missile warning, the report said. “Distinguishing a hypersonic heat signature against the Earth’s background has been likened to tracking a slightly brighter candle in a sea of candles, requiring extensive testing to validate.”

The author of the report, Masao Dahlgren, said models and simulations used for the study highlight the importance of “fire control” data — precise enough to guide an interceptor to shoot down the incoming missile. 

Dahlgren, a fellow at the CSIS Missile Defense Project, explained that having higher quality fire control data reduces the burden on the interceptor, and that is a key tradeoff that needs to be considered.

“If you have more precise data, you could use an interceptor that maybe wouldn’t need to maneuver as much and could be cheaper,” he said. Conversely, less precise data puts more of the burden on the interceptor to make up for weaknesses in the data. 

Sensor fusion — the process of combining data from multiple sensors to create a more accurate and complete picture of the environment — is another concern flagged in the report. Dahlgren compared it to the challenge of autonomous vehicles. Cars use a variety of sensors to navigate their surroundings, and sensor fusion helps to ensure that the car has a 360-degree view of its environment and can avoid obstacles.

In missile defense, “the challenge comes when you try to get data feeds from multiple satellites and integrate them into one target track,” he said. 

DoD now relies on a handful of missile-warning satellites, but the future low Earth orbit architecture currently in the works by the Space Development Agency will have dozens of tracking satellites. “How do you fuse that data into a common operating picture?” Dahlgren said. “We are moving fast to get those satellites up on orbit, but the capacity to fuse the data will be a bottleneck,” he added. “Sensor fusion is a hard engineering challenge.”

Tradeoffs in coverage 

The study suggests other tradeoffs could be considered in order to ensure coverage of the Indo-Pacific region, where Chinese hypersonic missiles might be deployed.

DoD’s planned multi-orbit architecture includes satellites in low, medium, geostationary and highly elliptical orbits.  

  • LEO constellations benefit from proliferation and economies of scale but suffer challenges with persistence and orbital lifespan, the study said. 
  • MEO constellations offer more coverage and persistence but require potentially costlier satellites with larger apertures 
  • GEO and HEO orbits require few satellites to selectively cover a given pole or longitude, but they are far more expensive. 
  • Airborne sensors can provide persistent coverage and are unbounded by spacecraft orbital mechanics but have smaller detection footprints and require basing locations to operate. 

LEO constellations in highly inclined orbits, for example, tend to under-cover areas near the equator, including critical parts of the Indo-Pacific region, the report said. MEO assets orbiting near the equator could complement the coverage.

The modeling and simulation tools used for the study include the ANSYS/AGI’s Systems Toolkit (STK) and Iroquois Systems/Lockheed Martin’s SMARTSet systems. Analysts created original 3D models of notional hypersonic weapons and imported infrared terrain data provided by NASA. Funding for the study was provided by General Atomics, L3Harris, Leidos and Lockheed Martin.

Sandra Erwin writes about military space programs, policy, technology and the industry that supports this sector. She has covered the military, the Pentagon, Congress and the defense industry for nearly two decades as editor of NDIA’s National Defense...