IRST21 (AN/ASG-34(V)1)

The IRST21 is the next-generation successor to the AAS-42 system.

When integrated into a pod for the F-15, the system is known as the Legion Pod (See separate record); when integrated into a fuel tank/ECU/sensor combination for the F/A-18, the system is known as the ASG-34(V)1 pod.

For the Navy Super Hornet, IRST21 is integrated in the front of the centerline fuel tank. For the Air Force, the IRST21 sensor operates in Lockheed Martin’s Legion Pod.

Infrared Search and Track (IRST) is a sensor that allows pilots to detect and track enemy aircraft without using radar, which means it can operate without giving away its position. This makes it particularly useful in situations where radar might be compromised or when stealth is crucial. The IRST21 system, an advanced version of earlier IRST technology, helps guide missiles like the AIM-120C/D and AIM-9X to targets that are beyond the pilot's visual range.

Lockheed Martin upgraded an older IRST system, the AAS-42, to create the IRST21 specifically for the F/A-18E/F fighter jets. The system was designed and tested between 2009 and 2011, eventually being integrated into a modified fuel tank on the aircraft, which is called the ASG-34(V)1. However, this integration reduced the fuel capacity of the tank to make room for the IRST electronics.

Because of the electronics integration, the fuel tank portion of the assembly, known as the FPU-13/A, has a reduced capacity versus the FPU-12/A tank it replaces. As reported by the U.S. DOT&E, the addition of the IRST's electronics reduces the centerline fuel tank's capacity from 480 gallons to 340 gallons.

On the F/A-18E/F, the Block I IRST21 sensor is paired with a first-generation, liquid-cooled, 6U, open architecture V1L processor, and utilizes an onboard IMU.

The F/A-18E/F's Block II IRST21 utilizes an IRST21 V3 sensor paired with the third-generation, liquid- cooled, 3U, open architecture V3L processor and an onboard IMU.

3D Capability. In May 2021, at the U.S.'s Northern Edge exercise in Alaska, a new IRST21 datalink capability was tested. The new operational mode allows pods, functioning on separate aircraft, to network, which gives the typically 2D output from the IRST21 the potential to be converted to a 3D dataset by utilizing the additional perspective provided by the second pod.

Origins. By the early 2010s, the technology in the AAS-42 infrared search and track (IRST) system had become outdated and needed improvements. Lockheed Martin, leveraging its experience from developing the AAS-42 and other systems like the Sniper targeting pod, began working on a new generation of IRST technology, which would eventually be called the IRST21.

The U.S. Department of Defense (DoD) saw the need for a modern, passive detection system that could be used on fighter jets in both the Air Force and Navy. While modern radars, including advanced AESA (Active Electronically Scanned Array) systems, have built-in measures to avoid detection, they still emit radio waves, which makes them inherently detectable. In contrast, electro-optical (EO) detection systems, like those using infrared (IR), ultraviolet (UV), or visible light, only sense incoming light and do not emit any signals, making them passive and much harder to detect.

Lockheed Martin's development of the IRST21 was aimed at creating a long-range detection and tracking system that could match the range of radar but operate passively, meaning it wouldn't reveal its presence. The U.S. DoD supported this effort by allocating research, development, testing, and evaluation (RDT&E) funds to Lockheed Martin, enabling the creation of the IRST21 for use on fighter aircraft like the F-15 and F/A-18E/F. This new system provides a significant advantage by allowing pilots to detect and track targets without being easily detected themselves.

In service.

The Navy and Lockheed Martin anticipate reaching Initial Operating Capability for the Block II system in early 2024.

The U.S. Air Force originated the IRST program in 1981. Based on initial successes, the program was expanded in 1986 when General Electric was selected to develop the IRST system for a joint USAF/Navy program. Under this program, GE was to provide an IRST system for the USAF's F-15 and the Navy's F-14 aircraft.

Lockheed Martin began work on the U.S. Navy's F/A-18E/F IRST program of record in 2008.

Development of the next-generation IRST system in support of the F/A-18 began in 2011 under a $135 million EMD contract.

In 2012, Lockheed Martin announced the system's successful performance of acquisition, tracking, and weapons cuing processes on board a testbed aircraft. The tasks were reported to have been performed during the system's first sensor pass while operating on board a King Air light aircraft.

Lockheed officially introduced the IRST21 in 2014. The Legion Pod was announced in 2015.

Active development to outfit the IRST21 to the F-15 began in Q1 of FY15 and continued through Q4 of FY18. In September 2016, the IRST21, as part of the Legion Pod, completed its first test flight on board an F-15C. At the time, it was reported that equipping the pod required no additional modifications to the host aircraft.

Deliveries of the LRIP ASG-34(V)1 pod for the U.S. Navy's F/A-18s – the pod contains the IRST21 Block I system – began in 2017; the pod had received production approval in January 2015. Full-rate acquisition of the matured IRST21 Block II in support of the F/A-18 was to begin with FY21 funding.

On Nov. 26, 2018, Lockheed Martin was awarded a US$108 million contract for phase II of the F/A-18E/F Super Hornet Block II IRST program for the U.S. Navy, awarded by Boeing.

The IRST21 was first fielded on F/A-18E/F aircraft in March 2019.

Australia released sources-sought notifications for procurement of 12 ASG-34s, following approval for local IRST21 production in March 2015 to equip Australia's F/A-18E/Fs. A contract to fulfill the requirement was awarded in April 2020.

On Nov. 17, 2020, announced the unveiling of the updated sensor suite for the F-16. The Legions-ES (Embedded System) was designed for the F-16 Block 70/72.

On June 8, 2021, Lockheed Martin introduced a new datalink for its Legion Pod, which includes IRST21 technology, enabling pilots to determine the range to targets more efficiently in contested air-to-air environments. Previously, IRST systems relied on other aircraft systems or pilot actions to estimate range, but the new datalink allows for near-instantaneous range calculation by enabling direct communication between pods.

In February 2022, the U.S. State Department approved Indonesia for procurement of 36 F-15IDs, at least some of which would carry ASG-34s. At time of press, a contract had yet to be awarded. An earlier contract for Dassault Rafales may supersede any Indonesian F-15ID acquisition.

The U.S. Dept. of Defense announced on Feb. 26, 2024, that Boeing was awarded an US$86.4 million contract to design, develop, and produce two prototypes and special test equipment for the AN/ASG-34A (V)1, supporting field testing for the U.S. Navy and Australia. The work, to be completed by February 2029, will take place in St. Louis, Missouri.

Lockheed Martin, Orlando, FL, USA

 Australia
   Air Force         [12] (ASG-34 Block II F/A-18E/F)

 USA
   Air Force/Navy      (F/A-18E/F)
                       (F-15 Legion Pod)

 WEIGHTS
   Sensor head              115 lb ( 52.2 kg)
   Processor                 42 lb ( 19.1 kg)
   Legion pod               550 lb (249.5 kg)

 DIMENSIONS
   Sensor head
      length                38.0 in (96.5 cm)
      diameter               9.2 in (23.4 cm)
   Processor 
      length                18.5 in (47.0 cm)
      height                 7.6 in (19.3 cm)
      width                  9.3 in (23.6 cm)
   Legion pod
      length                98.5 in (2.5 m)
      diameter              16.0 in (40.6 cm)

AN/ASG-34(V)1

The system is integrated into a modified centerline fuel tank (designated FPU-13/A), replacing the standard FPU-12/A tank. This integration reduces the tank's fuel capacity from 480 gallons to 340 gallons to accommodate the IRST electronics.

The AN/ASG-34(V)1 operates passively, meaning it does not emit signals like radar does. This allows the aircraft to locate and track enemy targets without revealing its own position.

Legion Pod

IRST21 variant optimized for the F-15. (See Legion Pod record.)

In April 2010, Lockheed Martin received a contract from Boeing to continue development of system requirements for a new U.S. Air Force F-15C IRST sensor system. The system would be based on the IRST technology created for the F/A-18E/F variant.

In February 2015, Lockheed Martin revealed that the integrated IRST21 variant optimized for use on board the F-15 would be known as the Legion Pod.

The baseline Legion Pod utilizes an IRST21 V2 sensor paired with the V2L processing unit, a second-generation, liquid-cooled, 3U, open architecture processor that receives additional information from an onboard IMU.

The Block II Legion Pod utilizes an IRST21 V3 sensor with a third-generation V3L liquid-cooled processor and an onboard IMU.

Compatibility with the IRST system aligns with the release of F-15 OFP 9.2.

Legion-ES

The Legion-ES (Embedded System) pod utilizes the technologies of the F-15's Legion Pod, but repackaged for use on board the F-16V Block 70/72, whereon it mounts on a forward-located point. Some of the Legion-ES's processing electronics are relocated from the interior of the pod into the aircraft's equipment bay, reducing the pod's size and weight in comparison to the F-15's Legion Pod.

The Legion-ES's IRST21 V2 sensor is paired with Lockheed Martin's V3A processor, a third-generation, air-cooled, 3U, open architecture processor that incorporates data from an onboard IMU.

The system weighs under 300 pounds measuring 77 inches in length and 9.75 inches in diameter.

The IRST21 is estimated to cost US$4 million to US$5 million.

Based on the U.S. Air Force's FY19 budget estimates, the Legion Pod costs an average of $3.120 million per unit. Including necessary support equipment, the price rises to $4.010 million.

Legion Pod (ISRT21 variant optimized for F-15)