Advancing radars for defense against missiles and hypersonic weapons

Ground-based radars are currently undergoing modernization, and a space-based layer of sensors is under development to help defend against ongoing threats posed by ballistic missiles and a newer one in the form of hypersonic weapons.

Hypersonic weapons fly at least Mach 5: Five times the speed of sound, or about 3,800 mph. Unlike ballistic missiles, which can reach similar speeds but tend to have a relatively fixed flight path, the U.S. Government Accountability Office (GAO) says that hypersonic weapons will be able to fly at lower altitudes and may even be able to change targets during flight. These capabilities make these weapons extremely difficult to defend against.

To address this, defense suppliers are stepping up their radar research and development efforts. For example, Raytheon (Waltham, Massachusetts) is evolving its ground-based ballistic missile sensors and effectors – the interceptors that shoot missiles down – every day within this ever-changing threat landscape.

“Our adversaries are developing and launching missiles that can maneuver,” says Erin Kocourek, director of business development for Raytheon’s ground-based missile defense radars. “It’s important to note that radars – our current radars today as well as the next generation – are able to track these things.”

A big concern is that coverage gaps exist in ground-based sensor:. “We simply don’t have enough ships and islands to put a ground-based radar to track everything, so there are coverage gaps around the globe,” she adds. “And maneuverable hypersonic glide vehicles can outfly current radars and go around them to avoid the search senses of existing radars today.” That’s part of the reason why there’s a lot of advocacy for adding a space layer.

“Left-of-launch” capabilities are also being explored to address hypersonic threats; this approach essentially involves taking missiles out in boost phase or even before they launch.

And it’s important to note that the ballistic threat isn’t going away. “Our adversaries have it and we need to develop next-generation sensing to address multidimension threats,” Kocourek says. “We have a very good missile defense infrastructure and are aware of the evolving threat, but we’re even getting out in front of it now.”

Raytheon’s ground-based radars are being upgraded to primarily provide more range, improve processing speed, and perform 360-degree sensing. Distributed sensing and integration of systems are also being explored.

Shift to GaN = More energy

Raytheon is upgrading its ground-based sensors to gallium nitride (GaN), which is a shift away from gallium arsenide (GaAs) sensors.

“The GaN-powered radars we’re building will have more energy or range, which extends the battlespace,” Kocourek explains. “We also want to take radars to 360 degrees. Some are already 360-facing, which means that you can see threats coming from multiple different locations. This reduces chances of targets or incoming missiles flying around your radars, so 360 degrees is very important to defeating next-generation threats.”

One example of a 360-degree radar built by Raytheon is its integrated air and missile defense radar, and it really starts with their SPY-6 radar baseline: “This is an integrated air and missile defense radar in production today, which will be on Flight III destroyers,” Kocourek says. “They’re completing tests this year, and there are several variants that can be designed as a rotator or fixed radar. From the ground side, we’re exploring the ashore versions of those – meaning taking them off a ship deck and putting them on the land.”

Raytheon is also upgrading the processors in its existing radars as well as its next-gen radars by “moving toward an x86 processor, which is faster,” Kocourek notes. “It goes along with the GaN upgrade – using a different power source for our radars.”

Radar size

Radars can be absolute monsters in size, particularly the legacy ones. “The mission drives the radar size,” Kocourek says. “Beyond scalability, the larger the aperture, the larger the radar size. But there’s only so much deck space on a ship, so we’re very focused on next-generation radars – especially in a distributed approach, with the ability to have both fixed and transportable or mobile radars. So reducing the footprint makes a lot of sense, but ultimately the mission is what drives the size of that radar.”

Homeland-defense radars require a big aperture, since there’s a considerable distance between some of our adversaries and the U.S. “There are some lower-tiered sensors, which are inside the atmosphere and generally track air-breathing threats,” she explains. “Counter-UASs [unmanned aircraft systems] generally have smaller apertures and footprints. Upper-tier sensors are going to have a larger aperture, but it really depends on the mission and what you need to see that drives radar size.”

Availability is also significant in terms of radar and which direction things are likely heading: “You don’t want to build a radar that’s so big that it far exceeds need or range requirements,” Kocourek points out. “So when we think of radars, we develop a radar architecture that allows for scalability – enabling efficiency, risk reduction, and cost considerations.”

Radar solutions must be uniquely scaled to the threat and the range for the defended area, geographic location, and mission. “These are critical considerations when you think about the size of your radar,” she says. “So we’re developing and architecting our next-generation radars with that in mind so that they’re almost like building blocks you can size up according to mission need.”

Distributed sensing

Distributed sensing is another key concept Raytheon is working on to improve missile-defense sensing capabilities. This concept involves combining different sensors to essentially work as a team.

“When sensors in different locations all form their beams toward one object, it acts like a flashlight,” Kocourek says. “With multiple flashlights on one object, you’re going to be able to discriminate and see what that object is, take a better look at it, and get a better description of it.”

Raytheon is currently exploring “netting together sensors with a distributed sensing approach because not only does it allow you to see and track an object better, it also provides for more resilience and survivability of the system,” she adds. “If one of your sensors gets taken out or isn’t operational for some reason, the rest of the architecture is still there and you’re still getting a picture of your target and can feed that information to the effector to shoot it down.”

Are sensors likely to be targeted and taken out? “It’s definitely a concern if we go to war. Big assets like sensors and critical infrastructure are always going to be targeted by adversaries, so we do our best to build them to withstand attacks,” Kocourek says. “But it’s not any more of a threat than it’s ever been. Certainly, our adversaries are continuing to develop their technologies and capabilities. So our primary goal is to deter through uncertainty and to have the capability to defend and protect our assets and our homeland, as well as those of our allies.”

Integration also key

Integration is another key role radars will be playing. “More than ever, we need systems that work together to increase the battlespace and defended area,” Kocourek says. “One of Raytheon’s radars, the AN-TPY, operates in two modes: forward-based mode – which means that it’s out there on its own tracking – and cueing other sensors to look.”

Raytheon has successfully demonstrated “engage on remote,” which can be explained this way: When an SM-3 missile gets launched off an Aegis cruiser, if it has its own organic sensor on it (a SPY-1), it can successfully track and cue a SPY-1 on the Aegis ship to launch a missile interceptor. “An off-board sensor, the AN/TPY-2, was able to track first and then send that cue through a data link, to a satellite communications network, and then back to that ship to do what we call ‘engage on remote,’” Kocourek explains.

Another example is the integration of Terminal High Altitude Area Defense (THAAD) and Patriot missile defense systems. “Proven systems can work together to increase the defended area,” Kocourek says. “U.S. Forces-Korea had an urgent operational need and used AN/TPY-2, which is part of the THAAD system comprised of a radar, launcher, and a command and control capability. The Patriot system, which is similar, has a sensor launcher. We combined those two to integrate for increased battlespace in U.S. Forces-Korea to meet this need. The AN/TPY-2 as part of that THAAD system, was able to see and give the Patriot a cue, which gave the regional commander a better defense picture and increased battlespace – providing more time to determine which asset to use to shoot down the incoming threat.” (Figure 1.)

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Figure 1 | U.S. Forces-Korea had an urgent operational need and used Raytheon’s AN/TPY-2, which is part of the THAAD system comprised of a radar, launcher, and command-and-control capability.

Space-based sensors to augment ground-based radar systems

Along with ground-based radars, space-based sensors are being developed for a proposed satellite constellation to help track hypersonic and ballistic missiles. A space-based sensing layer would ideally augment the existing missile defense architecture. From space what’s being done is persistent sensing, as opposed to ground-based sensing that’s often limited by the horizon.

Northrop Grumman (Falls Church, Virginia) was recently selected as one of four defense contractors to work on the Missile Defense Agency’s Hypersonic and Ballistic Tracking Space Sensor (HBTSS) Phase IIa Program. (Figure 2.)

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Figure 2 | Northrop Grumman’s concept of space-based sensing solution for hypersonic and ballistic missile defense advances under the HBTSS Phase IIa Program. Image courtesy of Northrop Grumman.

As part of this program, Northrop Grumman is developing a highly capable, survivable, affordable, and extensible space-based sensing solution for hypersonic and ballistic missile defense.

“HBTSS is an important undertaking that allows us to see advanced threats like hypersonic missiles in ways we haven’t been able to before,” says Kenneth Todorov, vice president of Missile Defense Solutions for Northrop Grumman. “If you can see the threats, you can take them out.”

Northrop Grumman’s end-to-end, multidomain approach to hypersonic and ballistic missile defense spans technologies within multiple warfighting domains from sea and space to the electromagnetic and cyber environment.

Future of hypersonic weapons

The U.S. Department of Defense has many programs underway by DARPA [Defense Advanced Research Projects Agency], the Air Force, the Navy, and the Army to develop hypersonic weapons for a wide variety of applications and launch methods, according to the GAO.

Tracking these hypersonic weapons is highlighted by the GAO as one of the key challenges the weapons pose, so research and development within this realm will be critically important for national security.

As far as a timeline goes, a U.S. Air Force Scientific Advisory Board report says that domestically, the core technologies necessary for the development of a tactical hypersonic glide vehicle have reached a technical readiness level (TRL) of 5 out of 9. The board expects the remaining subsystems for such weapons to reach a TRL of 6 or higher in 2020. According to GAO best practices, a TRL of 7 is the level of maturity that constitutes a low risk for starting system development – indicating that a technology has achieved form, fit, and function, and has been demonstrated within an operational environment.