WASHINGTON — The Space Development Agency (SDA) is considering flying satellites to track airborne moving targets when it launches its next iteration, called Tranche 3, of missile defense birds, outgoing agency director Derek Tournear told Breaking Defense in an exclusive interview.
“It’s all a little bit preliminary at this point. There’s discussions right now happening within the department, as well as with Congress, on the proper way to do that, and the timing of it,” he said.
“But the current plan would be to have that be part of Tranche 3, and have that solicitation go out fairly soon. But there’s still some deliberations going on on the exact details of what that would look like,” said Tournear, who announced his departure from SDA on Monday.
The Space Force, the Air Force and US Northern Command have been collaborating to demonstrate space-based sensors for the airborne moving target indication (AMTI) mission as a partial replacement for the Air Force’s venerable E-3 Sentry sometime around 2030, although officials have been coy about providing details. That date is now somewhat in question due to the Trump administration’s plan to cancel the E-7 Wedgetail designed to replace the E-3.
The Space Force’s former deputy for operations, cyber and nuclear, Lt. Gen. DeAnna Burt — who retired mid-August — said in an Aug. 1 speech that the service is in the midst of an analysis of alternatives on space-based AMTI that is expected to wrap up this fall.
The idea, Tournear said, would be to bring on the new AMTI satellites as part of SDA’s so-called missile custody layer — which in turn is part of the agency’s overarching Proliferated Warfighter Space Architecture (PWSA) comprising hundreds of satellites in low Earth orbit (LEO).
SDA has defined its potential custody layer as a hybrid constellation of government and commercial satellites to provide operators with near-real time ground target tracking and targeting information.
“When we talk about custody layer, we talk about target custody, right? I’ve always said that that is our ability to detect and track moving targets on the ground and sea, and now also in the air,” he said.
In the past, Tournear said he “always caveated” that SDA itself was “not really looking at building out a lot of the custody satellites,” and instead was planning to turn to others, including the Air Force, the Intelligence Community and the commercial sector already involved in developing and building intelligence, surveillance and reconnaissance satellites. Those partner birds then would be tied in the PWSA and its Transport Layer data relay constellation.
“But now things have changed a little bit, and SDA is actually looking at flying AMTI satellites as part of our custody layer,” he said.
The AMTI birds would carry “radar-based systems” for spotting missiles in flight, Tournear added.
“Is that easy? No, it is incredibly difficult,” he said.
The primary problem is that due to the laws of physics, satellites in LEO orbit at an extremely fast rate, remaining over the Earth horizon for only about seven to 10 minutes. Missiles — whether ballistic, cruise or hypersonic — also are screaming through the atmosphere at super high speeds.
The capability of any radar system is “a function of power and an aperture, aperture meaning essentially your antenna size,” Tournear elaborated, noting that the closer a radar is to the target the more you can reduce power and antenna size requirements. (Lower power, smaller size translates into lower costs.)
“That’s where proliferation helps you,” he said. “If you throw up more and more satellites, that means at any given time there’s a chance that the aircraft flying around will be fairly close to to the satellites. … And that’s one of the main ways that you overcome the difficulty of AMTI.”
Of course, he added, another approach is to increase the size of the antenna.
“Historically that has been prohibitively expensive. And that’s why this has never been done from space before. It cost too much to build very large antennas and field them,” Tournear said. “But there’s been so many advancements in the commercial industry. … There’s several companies out there that are building very affordable antennas that could be proliferated to be able to enable this mission.”
The upshot, he asserted, is that space-based AMTI is now doable.
“I would say that we are at the point now where the technology has matured and it’s commoditized, so that radar based AMTI from space is feasible.”