Although the classified budget may cloak U.S. efforts to develop a space-based ground moving target indicator (GMTI) radar, the Department of the Air Force’s fiscal 2022 request sheds some light on research and development on a space-based GMTI radar recently disclosed by U.S. Space Force Chief of Space Operations Gen. John “Jay” Raymond.

“The space-based GMTI system has its own funding line, which is part of the United States Space Force (USSF) total obligation authority (TOA),” per a June 2 email from U.S. Space Force’s (USSF) Space and Missile Systems Center at Los Angeles AFB, Calif. “The budget for research and development and/or procurement of the space-based GMTI system is being managed through normal Department of Defense (DoD) processes. No further information is available at this time.”

Raymond said last month that Space Force is “building GMTI from space” by using “the full spectrum of options,” including trying “to leverage commercial more than we’ve done in the past” to drive competition (Defense Daily, May 12).

Space GMTI is to provide time critical targeting without putting airborne assets, namely the aging Northrop Grumman [NOC] Joint STARS aircraft, at risk.

In 1999, when Joint STARS achieved full operational capability for the Air Force, no space-borne GMTI satellite had flown, but since then, such a space-based GMTI capability has shown promise, including on a Canadian RADARSAT-2 experiment and the Chinese Gaofen-3 low Earth orbit remote sensing satellite.

In 2000, a control failure in NASA’s Shuttle Imaging Radar Topographic Mission “inadvertently created an along-track interferometry (ATI) Synthetic Aperture Radar (SAR) imaging geometry that was used to show that space-based SAR-GMTI could be used to detect moving vehicles on a highway for a couple of example cases,” per a  2012 technical report by the Canadian government.

USSF, in its unclassified research and development fiscal 2022 request for aerospace sensors, has about $50 million for efforts that may inform space-based GMTI.

For example, USSF asks for $19.9 million for “distributed radio frequency sensing” to “develop innovative, timely, and affordable target detection, tracking, and characterization (namely imaging/identification) capabilities that leverage two or more spatially-distributed receivers and transmitters that use cooperative radio frequency transmitters (illuminators), namely those radio frequency sources that have a common objective to the receiver systems being used.”

Under this effort, in fiscal 2022, USSF plans to continue development of “robust multi-static transmit waveforms and receive processing chains for operationally relevant multistatic ground moving target indicator systems,” and development of “clutter mitigation techniques for multi-channel distributed sensor systems to detect slow-moving targets in denied environments,” according to budget documents.

USSF also wants to begin assessing multi-static synthetic aperture radar algorithms to support rapid combat identification and automatic target recognition requirements and to demonstrate such algorithms on low cost, size, weight and power platforms.

Academic literature has discussed Space-Time Adaptive Processing, a modern radar signal processing technique, for space-based GMTI to cancel background clutter and detect slow-moving targets.

In January, Chinese researchers noted the promise of a geosynchronous, multistatic synthetic aperture radar on small satellites in acquiring multi-channel data for GMTI in a cluttered ground environment.

Raymond said last month that the USSF space GMTI mission “is something that I’d keep an eye on,” when asked what USSF tactical intelligence, surveillance and reconnaissance programs analysts should watch.

The new USSF tactical mission areas will not conflict with the Space Development Agency (SDA) effort to field a National Defense Space Architecture, SDA Director Derek Tournear has said.