In a world where U.S. peer competitors and rogue countries possess the capability to conduct missile-based nuclear strikes, a persistent space-based defense is the only way to ensure we're never surprised by or unprepared to defend ourselves against such attacks.

"To protect the U.S., we want to get notification of any missile launches as early as possible from anywhere on the globe," explains Jenny Newbury, thread lead for Overhead Persistent Infrared (OPIR) performance on Northrop Grumman's Next-Generation Polar (NGP) satellite program. "But we also don't want to wake up the president with a false alarm."

NGP satellites comprise the polar-orbiting component of the U.S. Space Force's Next-Generation OPIR program, the nation's newest missile warning system. Northrop Grumman serves as the Space Force's prime contractor for NGP. The company is also developing sensor payloads for Next-Gen OPIR satellites operating in geosynchronous orbits (GEO).

Ensuring Persistence

Not surprisingly, infrared technology is central to the OPIR mission.

"A boosting missile is very hot, so we always want to look for that heat in the infrared portion of the spectrum," advises Newbury. "The advantage of monitoring the Earth from space, of course, is that you can watch the entire disk of the Earth for missile launches in a steady, persistent way."

Satellite infrared technology can also be used to detect and provide early warning to populations on Earth about forest fires, she adds.

Northrop Grumman has been developing early warning satellites since the 1960s when it produced 12 Vela satellites designed to detect nuclear tests in space and the atmosphere. The company also designed and produced the nation's GEO constellation of Defense Support Program early warning satellites, which became the spaceborne segment of the North American Aerospace Defense Command's Tactical Warning and Assessment System in 1970.

Optimizing the Constellation

Since missile attacks can originate anywhere on the globe, developing and maintaining an effective space-based defense system requires deploying missile warning satellites in a variety of orbits.

Current missile warning systems typically use four to six GEO satellites and two satellites in highly elliptical (polar) orbits (HEO), advises Newbury. While GEO satellites have a fairly direct view of the "middle" two-thirds of the Earth disk, their views of the poles are limited by their oblique viewing angle of those regions.

"Satellites in HEO can look straight down at the poles," says Newbury. "That's significant because the quickest route to the U.S. for a ballistic missile traveling from China, Russia or North Korea would go right over the North Pole."

The other advantage of HEOs, she adds, is that you can always downlink sensor data directly to the U.S., which is good from a security perspective.

Choosing the Best Infrared Technology

Space-based defense systems typically use several IR frequency bands.

"When we're trying to detect missile launches as early as possible, we use shortwave infrared technology, which allows us to see through the atmosphere, all the way to the ground," explains Newbury. "Unfortunately, with those IR frequencies, we also get a lot of clutter, i.e., things that look like detections but aren't."

That's where mid-IR and long-wave IR signals come in handy, she adds. These signals are absorbed by the Earth's atmosphere, so once the missile rises above the clouds, satellite sensors can see it and track it easily against a plain background.

"If you want to get a closer look at that missile or warhead, you'll also need two or three satellites in low Earth orbits (LEO) to get an accurate track. These satellites tend to have sensors operating in a variety of bands."

Engineering the Mission

Designing and optimizing a space-based defense mission — deciding everything from how many satellites to put in orbit and what types of sensors should be used, to how best to process and relay data to ground operators — is the domain of seasoned mission engineers like Steven Warwick, mission performance modeling and simulation lead for Northrop Grumman's OPIR and Geospatial Systems business unit.

"We start with how is this data going to be used, who's going to be using it and what are they trying to achieve with it?" he explains. "Once we know why we need the data, we can optimize our approach for getting it."

Warwick and his team use orbital visualization tools such as the system tool kit (STK) and an internal Northrop Grumman-developed tool called Thorn to define the optimum geometry of satellites for achieving the desired space-based defense mission.

"Mission engineers model different types of targets traveling on different trajectories with unique thermal signatures to see how they look against the Earth under different atmospheric conditions," Warwick clarifies. "We also rely on skilled Northrop Grumman mission analysts to identify how best to correlate an observed threat profile with a particular type of target."

Ensuring Attribution

Strategically, Warwick suggests, the name of the game in missile defense is attribution.

"We want to be very sure of who launches an attack against us but also to let our enemies know that we have a system that will absolutely tell us who launched an attack against us," he says.

Warwick hopes that such a scenario never plays out, of course, but the rules of an effective space-based defense remain ironclad.

"If we detect a launch, we must produce a high-accuracy track of that missile, and then retain 'custody' of that track to ensure that we can predict where it's going to land," he says.

Maintaining Track

Achieving and maintaining that track, however, requires significant data processing.

"The large-format focal planes of early warning satellites gather hundreds of millions of pixels of threat data per second, which can stress the capabilities of a typical comm downlink," Warwick suggests. "In that case, a satellite will do some processing on board to try to identify the pixels that matter most and send those pixels to the ground for further processing."

The key challenge, he stresses, is to keep the true detections and throw away the false ones.

Maintaining track of an incoming target is also being challenged by evolving weapon technology, Warwick says.

"Traditional ballistic missile warheads, once separated from their booster, follow a gravity-driven trajectory, which makes it relatively easy to determine their point of impact," he explains. "By contrast, hypersonic weapons, once released, begin maneuvering at the very top of the atmosphere, which makes them much more difficult to track."

Rethinking the Mission

Newbury believes that hypersonic weapons may also be changing the way her customers think about how best to track and engage these more advanced targets.

"I think there's more utility for LEO and medium Earth orbit (MEO) systems where you want to get closer to your target," she says. "I also expect to see increased use of sensors operating in different parts of the spectrum to track newer targets that are very dim and may be maneuvering."

Northrop Grumman is well positioned to address this mission, Newbury believes, because of its development of two Space Tracking and Surveillance System (STSS) demonstrator satellites for the U.S. Missile Defense Agency in the early 2000s. Now retired, the STSS satellites proved the ability to use infrared technology to detect missile launches, track missiles from boost phase through midcourse flight, and communicate with missile defense command and control forces on the ground.

Meeting New Challenges

However it shakes out, claims Newbury, the U.S. is rising to the challenge of detecting increasingly sophisticated missile threats.

"The big difference between current U.S. space-based missile warning systems and Next-Gen OPIR is that the payloads will be faster and better," she says. "We're basically using the same payloads for GEO and HEO, which will give us much larger views of the polar areas."

The payloads for NGP, she continues, will not only perform traditional onboard processing of missile warning data but will also be able to download all of those pixels to the ground on every pass. This new capability will enable analysts on the ground to develop new missile warning and tracking algorithms from the raw data while also allowing payload engineers to evaluate the payload's health and performance.

FORGEing the Future

The nation's newest space-based defense systems, Newbury continues, will also be the first to become a part of the Space Force's new Future Operationally Resilient Ground Evolution (FORGE) Mission Data Processing Application Framework (MDPAF), as Raytheon Intelligence & Space explains.

"Traditional missile warning satellites have been designed to communicate primarily with their own network of ground stations," she notes. "By contrast, the FORGE framework is designed to take in data from lots of different satellite systems and exploit it for the benefit of all users."

Delivering Confidence

Ultimately, counsels Warwick, space-based surveillance and tracking are all about protecting the U.S. from missile attacks.

"The number-one job of our space-based defense system is to provide a track of high enough accuracy and low enough latency to give a ground-based interceptor the opportunity to do something about it," he says. "You better not say there's been a missile launch when there isn't one, and you better not miss one."

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