Hypersonic weapons break all the rules of the missile defense game.

With speeds surpassing Mach 5 and the ability to maneuver mid-flight, hypersonic weapons defy the missile defense status quo, potentially making the United States’ current defenses obsolete. China and Russia are vigorously pursuing hypersonic weapons, and the United States is desperate to neutralize them.

“China is also developing increasingly sophisticated ballistic missile warheads and hypersonic glide vehicles in an attempt to counter ballistic missile defense systems,” Defense Intelligence Agency Director Robert Ashley said in his March 2018 Worldwide Threat Assessment. “Russia claims a new class of hypersonic glide vehicle under development will allow Russian strategic missiles to penetrate missile defense systems. Iran is pursuing long-range, precision land-attack cruise missiles as well as development of more powerful space launch vehicles — boosters that would be capable of ICBM [intercontinental ballistic missile] ranges if configured for that purpose.”

The Space Development Agency and the Missile Defense Agency have a plan: a proliferated low-Earth orbit constellation comprised of hundreds of satellites capable of detecting and tracking hypersonics. And Congress appears to be supportive of the concept. Both the House and Senate opted to include $108 million for a hypersonic weapons tracking layer in space in the national defense policy bill, which was on the MDA’s list of unfunded priorities.

Some in the national security community believe a space sensor layer is the key to meeting the hypersonics threat, but what exactly is the hypersonic threat and how would a space sensor layer change things?

The hypersonic threat

Here’s how the United States’ current missile defense architecture is supposed to work: An adversary launches a ballistic missile bound for a friendly target. The Air Force’s Space Based Infrared System in geosynchronous orbit detects a launch and informs the rest of the missile defense system. An array of ground, space and naval sensors are used to track the missile to predict its trajectory, and an intercept missile is fired to destroy the missile. Problem solved.

Hypersonics upend those assumptions.

Far from traveling on a predictable arc through the atmosphere before returning to Earth, hypersonics are capable of changing course mid-flight. Not only does this make it more difficult, if not impossible, to plot out an intercept course — experts speculate some hypersonics might be able to maneuver around radar coverage, effectively neutralizing one of the military’s key missile defense sensor components.

“All of this is going to require more comprehensive birth-to-death tracking of these delivery systems,” said Thomas Karako, senior fellow at the Center for Strategic and International Studies and director of the think tank’s Missile Defense Project.

At the same time, hypersonics can reach incredible speeds, with some weapons surpassing Mach 5. The speed drastically narrows the time window when the military can intercept the weapon, making early detection and tracking all the more important. But hypersonics are designed to make early detection difficult.

According to testimony delivered April 3 by former Lt. Gen. Samuel Greaves, then the head of the MDA, to a Senate Armed Services subcommittee, hypersonics are far dimmer for tracking tools than most objects the military follows from space.

The current missile defense system was designed for ballistic missiles, not hypersonics that are faster, less predictable and harder to detect. Can it be adapted or augmented to effectively stop hypersonics?

Sensing from space

Enter the idea of a space-based sensor layer.

“It’s the only solution for tracking a maneuvering delivery system like a hypersonic glide vehicle,” Karako said. “The reason for that is geography, or rather the shape of the Earth. You can try to fight the curvature of the Earth, and you will lose every time.”

The Missile Defense Agency’s 2019 Missile Defense Review elaborates further:

“The wider view from space allows for improved tracking and potentially targeting of advanced threats such as HGVs, which fly at lower altitudes than ballistic missiles and can maneuver throughout their trajectories to avoid some radar coverages. This capability would also provide the ability to track the dim upper stage of some ballistic missiles. This capability will be necessary to provide the tracking information needed for defense against HGV threats in the future.”

The idea of using space-based sensors to detect and track missiles is nothing new for the United States, where they are already play a critical role in the country’s missile defense system. What’s unprecedented here is the scale of a space-based sensor layer.

Today, the Pentagon relies on the Air Force’s Space Based Infrared System, which consists of four geosynchronous satellites and two payloads hosted on classified satellites in a highly elliptical orbit. SBIRS is used to detect missile launches, providing an early warning for the entire missile defense system. The Air Force is working on a SBIRS successor, the Next Generation Overhead Persistent Infrared, or OPIR, system, to provide increased capabilities.

The Missile Defense Agency controls two other missile warning systems: the Space Tracking and Surveillance System and the Space-based Kill Assessment system. STSS consists of just two experimental satellites that can track ballistic missiles in the boost phase and mid-course. The Space-based Kill Assessment program, which was launched into orbit in 2018, consists of sensors hosted on commercial satellites that are capable of detecting successful missile interceptions.

These sensors have proven to be an effective part of the United States’ missile defense system — at least when it comes to traditional ballistic missiles. But hypersonic weapons present new challenges, and the current space architecture isn’t good enough.

Now, the Space Development Agency and the Missile Defense Agency envision a proliferated low-Earth orbit satellite constellation made up of hundreds of satellites capable of detecting and tracking hypersonics.

“MDA is working with the (SDA), [the Defense Advanced Research Projects Agency] DARPA, and the U.S. Air Force to conduct prototype concept design activities for a space-based missile tracking sensor system known as Hypersonic and Ballistic Tracking Space Sensor,” Greaves said. “As part of an integrated multi-tier OPIR enterprise architecture, HBTSS would detect and track additional and emerging threats using persistent infrared sensors.”

Greaves also noted that the Space Tracking and Surveillance System, which operated in low-Earth orbit, served as a test bed for the hypersonic tracking layer.

The new satellites would be one of many layers being built into what the Space Development Agency, or SDA, envisions as a proliferated space architecture comprised of hundreds of small satellites. The agency was established in March to quickly create a layered architecture that would provide more resiliency for several space missions, to include a tracking layer.

An additional benefit to including the hypersonic tracking layer in the SDA’s architecture is that it allows for system updates more quickly than existing satellite programs, said Joy Stein, who is in charge of developing the tracking layer for the SDA.

Take SBIRS, for instance, a system comprised of large, expensive satellites. Once in orbit, it is practically impossible to upgrade the hardware on the satellite. While slight changes can be made to future satellites in the system, upgrades on a whole are limited. To drastically increase the capabilities and install more sensitive sensors in space, the Air Force decided to develop an entirely new system to replace it with OPIR.

In contrast, the SDA’s architecture is built around the idea of using hundreds of small, relatively cheap and easily replaceable satellites. By reducing the cost of putting additional satellites into orbit, the SDA hopes to make it easier to get more advanced sensors into space more quickly.

The SDA’s goal is to provide technology upgrades to all of its systems every two years. That method will allow the SDA to get new technology into space as soon as it’s operational instead of waiting until the system is fully developed because, the thinking goes, the upgrades can be sent up in the next batch.

“The SDA is going to incorporate all of the features of HBTSS into our architecture,” Stein said. The agency may begin launching sensor payloads before the full hypersonic tracking system is fully developed. Not only will that allow the tracking layer to meet the challenge presented by hypersonic weapons, it will also allow the military to more rapidly adapt to new threats that arise.

“The architecture has to allow for innovation and flexibility because we don’t know what we’ll need it to do next,” she said.

The SDA wants to have tech demo satellites in orbit by 2021, adding more satellites in subsequent years to reach full capacity.

While the SDA has received mixed support from Congress this spring, legislators seem to be more uniformly behind the concept of a space-based sensor layer.

“Congress on a very bipartisan basis is supporting this,” Karako said. “And that’s a good thing, but now we have to actually move out with this in a programmatic way.”

Despite its relatively rapid approach to development, Karako said, the Pentagon is not moving fast enough to counter hypersonic weapons, and part of the problem is the department’s home for the program. As the SDA is only a few months old, he questioned whether giving the space-based sensor layer to the agency instead of leaving it with the MDA was the right decision.