AIR-B21-Bomber
The USAF’s B-21 Raider strategic bomber, an artist’s rendering of which is seen here, will have the world’s most advanced integrated self-protection system when it enters service early next decade.

When it enters service from circa 2030, the US Air Force’s Northrop Grumman B-21 Raider strategic bomber will likely be the most advanced aircraft in the sky.

New strategic bomber

Tasked to deliver conventional and nuclear ordnance it will replace a trio of USAF strategic bombers namely the Rockwell International/Boeing B-1B Lancer, Boeing B-52H Stratofortress and Northrop Grumman B-2A Spirit. The B-21 will be the first new strategic bomber for the air force since the B-2A entered service in January 1997. The B-2A is arguably best known for its distinctive shape and use of advanced materials to reduce the aircraft’s Radar Cross Section (RCS). The B-21 will pick up where the B-2A left off employing the latest RCS reduction techniques and self-protection systems to enhance the aircraft’s survivability in robustly contested airspace.

Legacy

That BAE Systems has been selected to supply the electronic warfare system to equip the B-21 provides some interesting clues for its potential design. The company has furnished the electronic warfare systems for the last two USAF fifth-generation fighters namely the AN/ALR-94 equipping the Lockheed Martin F-22A Raptor and the AN/ASQ-239 furnishing the Lockheed Martin F-35A Lightning-II.

AN/ALR-94

Precise details of the AN/ALR-94 are Spartan. It is known to use antennas mounted on the aircraft’s wing leading edges and outer trailing edges, and on the inner trailing edges of the horizontal tail. These are thought to detect emissions from hostile radars transmitting across wavebands of 300 megahertz/MHz to at least 40 gigahertz from ranges of over 250 nautical miles (463 kilometres).

The AN/ALR-94 is linked to the aircraft’s BAE Systems’ AN/ALE-52 countermeasures dispenser and Lockheed Martin AN/AAR-56 missile approach warning system.

AN/ASQ-239

The AN/ASQ-239 uses the AN/ALR-94 as its baseline. The ensemble includes two radar warning receivers on the wing leading edges, two Radar Warning Receivers (RWRs) positioned close to the wingtips on the wing trailing edges and on the aft horizontal stabilisers, with additional RWRs either side of the aircraft’s exhaust. These provide the F-35A/B/C with full 360 degree coverage.

Although no details appear to have been publicly released it is thought that the AN/ASQ-239 can detect hostile radars transmitting in a two gigahertz to 20GHz waveband.

EW System B-21

Given BAE Systems’ involvement in these two systems, and its subsequent involvement in the B-21, it would be reasonable to assume that the electronic warfare system destined to equip this aircraft will use elements of the AN/ASQ-239 as its baseline, while adding some major enhancements.

To start with the B-21 self-protection system may cover a wider waveband than the latter. This could see an extension upwards to 40GHz and possibly beyond, and downwards to 500 megahertz, and maybe lower.

Bandwidth extensions

These bandwidth extensions could be driven by two threats: The extension to 40GHz will permit the detection of airborne, ground-based and naval surveillance and fire control radars, and radar guidance systems used in air-to-air and surface-to-air weapons.

So-called ‘millimetre wave’ radars transmitting on frequencies of 30GHz and above are in vogue. In a military context this comprises radars transmitting in Ka-band (33.4GHz to 36GHz) and above. Such frequencies are attractive. Ka-band transmissions have wavelengths of between 9mm and 8.3mm allowing these transmissions to depict targets in precise detail.

For Air-to-Air and Surface-to-Air Missiles (AAMs/SAMs) this enables the highly precise targeting of a hostile aircraft.

Cognitive EW

It would be surprising if the aircraft’s EW capabilities did not include cognitive approaches. The last five years has seen frequent discussion of cognitive EW and its potential contribution.

In a nutshell cognitive electronic warfare will see EW systems using software which records and analyses the system’s previous performance and then adapts its behaviour according to its current situation.

For instance, an electronic attack system may have successfully used a particular jamming waveform against a particular ground-based air surveillance radar during previous missions. Upon encountering a similar radar again the EW system will know to use that same waveform for the desired effect. If, on this occasion, that jamming waveform does not work, or only works if adapted in a particular way, the EW system will learn and take this into account the next time a similar radar is encountered.

The B-21’s self-protection system may even be capable of receiving live SIGINT (Signals Intelligence) updates across tactical datalinks concerning the radar threats it could encounter during its mission as and when these threats are determined by off-board sensors. These could include Low Earth Orbit SIGINT gathering satellites. Possessing such intelligence would allow the B-21 to perform instantaneous reactive jamming, and even pre-emptive jamming, prior to the aircraft encountering these threats.

However, the efficacy of any cognitive EW system will be highly reliant on robust, wideband communications so that the system can be uploaded with the latest threat information culled from these off-board sensors. Thus the aircraft’s communications will need to work closely, and be compatible with, the bomber’s EW systems.

Combat Cloud

There have been notable discussions in the US Air Force academic community regarding the development of a so-called ‘Combat Cloud’ upon which threat information could be uploaded as and when gathered, and then instantly downloaded into platforms needing this information. The Wright Flyer Paper entitled The Combat Cloud: Enabling Multidomain Command and Control across the Range of Military Operations published by the USAF’s Air University in 2019 provides more information relating to this concept.

Decoys

In terms of hardware, the B-21 may also seek to further exploit off-board decoys to jam and seduce hostile air defences. Raytheon’s ADM-160 MALD (Miniature Air Launched Decoy) series has been in service with the USAF since earlier this century.

The decoy is programmed to emit RF (Radio Frequency) energy in such a way as to mimic the RCS of a host of combat aircraft flown by the USAF. The intention is to fox air defenders regarding which aircraft is genuine and which is not. These decoys are launched when the aircraft is in hostile airspace.

The latest variant, the ADM-160C MALD-J, adds a jammer. This provides the decoy with an additional stand-in electronic attack capability.

DRFM Technology

Ongoing advancements in DRFM (Digital Radio Frequency Memory) technology could mean that future variants of the ADM-160 carried by the B-21, or a successor system, could transmit a host of innovative and discreet jamming and seduction waveforms, and may even incorporate cognitive EW techniques. The same may also be said of any towed decoy equipping the bomber.

Moreover, the aircraft may launch active RF decoys using its countermeasures dispensers. Leonardo has pioneered such a concept via its BrightCloud family of RF decoys. These are now entering service with the RAF. They are designed to provide a last ditch defence against incoming active radar homing AAMs and SAMs.

The B-21 will be the world’s most advanced military aircraft. Air defenders will have to acknowledge the fact that they will be facing the most advanced aircraft integrated self-protection system the world has ever seen.

by Dr. Thomas Withington