The U.S. Air Force plans to retire its 12 remaining Northrop Grumman [NOC] E-8C Joint Surveillance Target Attack Radar System,(Joint STARS) ground moving target indication (GMTI) planes–eight in fiscal 2023 and four in fiscal 2024–and to use other intelligence, surveillance, and reconnaissance (ISR) assets to fill in for the loss of Joint STARS.

“We continue to operate multiple ISR platforms with GMTI capability and plan to do so across the duration of the coverage reduction caused by JSTARS retirement,” the Air Force said in a March 28 email response to questions.

The first two Joint STARS developmental aircraft gained prominence during Operation Desert Storm in 1991 for their role in tracking and targeting Iraqi units and equipment, including Scud missile launchers. The U.S. also used Joint STARS during operations thereafter in Kosovo, the Middle East and Afghanistan–conflicts in which the U.S. used Joint STARS to track and target enemy units or to force such units to disperse, camouflage themselves, and dig in, in which case U.S. and allied ground forces were able to target or bypass them.

Dynamic GMTI radars, as on Joint STARS, allow periodic updates and precise tracking of moving targets via the Doppler returns of such targets.

Other Air Force aircraft besides Joint STARS with GMTI include the U-2 with the

Raytheon Technologies [RTX] ASARS-2 radars, the Northrop Grumman RQ-4B Block 40 Global Hawk with the Raytheon AN/ZPY-2 radar, and the RQ-170 Sentinel by Lockheed Martin. The Advanced Battle Management System (ABMS)–the Department of the Air Force initiative under Pentagon Joint All Domain Command and Control (JADC2)–is to aid the integration of such sensor information for time critical targeting.

Air Force Secretary Frank Kendall has suggested that the sustainment costs for Joint STARS are too high and that the aircraft needs replacement. The U.S. Space Force has been working with the National Reconnaissance Office (NRO) to develop and field a Space Based Radar (SBR) in the near term to provide GMTI for potential conflicts with adversaries able to deny airborne GMTI coverage by the U.S. (Defense Daily, Sept. 27, 2021).

While Chief of Space Operations Gen. John “Jay” Raymond disclosed the SBR effort last year and suggested that more details were forthcoming, the Department of the Air Force has revealed no such details and did not discuss SBR during a fiscal 2023 budget briefing. The Air Force said this week that the effort to provide GMTI beyond Joint STARS is classified.

Kendall said late last year that he had entered into discussions with NRO Director Chris Scolese and Director of National Intelligence (DNI) Avril Haines on coming up with the right mix of air and space sensors for GMTI. The NRO has traditionally provided intelligence gleaned from space sensors to the national command authority, not military forces in the field.

Space-based GMTI has shown promise in other nations’ research efforts, including the Canadian RADARSAT-2 experiment and the Chinese Gaofen-3 low Earth orbit remote sensing satellite.

The U.S. has initiated space-based GMTI efforts before–efforts that entailed cost estimates in the tens of billions of dollars for an operational system. In 1998, the Air Force, Defense Advanced Research Projects Agency (DARPA), and the NRO began the Discoverer II program to explore high-resolution space-based GMTI, but Congress canceled the program in 2000.

In 2004, the Air Force awarded a Lockheed Martin [LMT] team a contract for Space Radar, but the Pentagon killed the program in 2008 as being too costly.

A 2007 report by the Congressional Budget Office (CBO) estimated the cost of a space-based GMTI radar system as ranging from nearly $26 billion to more than $94 billion.