Lockheed Martin has packed the F-22 with sophisticated tactical intelligence systems, but – in a throwback to a pre-networked era – no means of transmitting data to other aircraft.

The need to preserve the F-22’s stealth signature has trumped all previous attempts to solve the problem. A decade ago, the US Air Force rejected proposals to integrate the non-stealthy Rockwell Collins tactical targeting network technology (TTNT) on the Raptor. The Lockheed F-35’s Harris-built, multifunction advanced weapon datalink (MADL) is a secure transmitter, but it was also rejected over concerns that its six antennas would affect the F-22’s stealthy skin.

The networking problem never went away, however, and now a new wave of technology has emerged with the goal of connecting a fifth-generation fighter such as the F-22, with fourth-generation types like the Boeing F/A-18E/F Super Hornet.

Northrop Grumman recently announced a “fifth-to-fourth”-generation networking system called the Freedom 550 radio, which uses a stealthy new dual-band antenna developed by Honeywell.

Northrop’s announcement comes just two months after Lockheed unveiled details of Project Missouri – a flight demonstration performed in December 2013 in which an F-22 passed data to a surrogate F-35 without compromising its electronic stealth signature.

Both proposals are now set to compete for an advanced tactical datalink (ATDL) programme, although funding and timelines remain unclear.

The proposals offer radically different ways of solving the networking problem between the F-22 and other aircraft.

Northrop’s approach avoids the potential cost and complexity of integrating new technology on the F-22. The company instead proposes to add the Freedom 550 to other aircraft, including the F-35, fourth-generation fighters, bombers and support aircraft – such as the Northrop E-2D Hawkeye and Boeing E-3A AWACS airborne early warning and control system platforms.

As a software defined radio, the Freedom 550 could also be added to the battlefield airborne communications node (BACN) – a network system payload carried today by the Northrop RQ-4 Block 20 Global Hawk and a modified Bombardier Global Express business jet, the E-11A.

Lockheed, however, takes the opposite approach. Rather than integrating a new radio on the rest of the fleet or being dependent on line-of-sight connectivity with the BACN payload, it proposes to install a secure radio made by Rockwell Collins on the F-22.

Software and hardware for the new Rockwell Collins radio – along with two L-3 Communications “devices” to encrypt and secure its transmissions – was developed in less than seven months, before being integrated on the F-22 and tested within 30 days, Lockheed says.The company shortened the integration process by using networking standards provided by the USAF and an unmanned air systems standards group. Lockheed estimates it would have taken 60% more time to develop new hardware and software on its own.

The flight tests in December showed that the new Rockwell Collins radio allows the F-22 to transmit and receive data using Link 16 – a data network developed in the 1970s and deployed on thousands of military aircraft, including the F-35. Lockheed uses a Link 16 waveform with a low probability of interception and detection, meaning the F-22's transmission is unlikely to betray its position to radio frequency detectors.

As a fighter commissioned in the midst of the Cold War, the F-22 was designed to maximise low observability to radar and other electronic signals. The USAF omitted Link 16 from the F-22’s operational requirements, but gave the fleet the intra-flight datalink (IFDL). The IFDL allows an F-22 to exchange data with other F-22s on a secure waveform unlikely to be intercepted by enemies or jammed. In operations, the F-22 is known to use the IFDL to pass radar tracks to a Raptor flying far ahead that is not using its radar to avoid detection by an enemy’s sensors.

Access to Link 16, however, opens critical opportunities for the F-22 fleet. Finally, the type can automatically pass along data in flight from its two most sophisticated sensors – the Northrop APG-77 active electronically scanned array (AESA) radar and the BAE Systems ALR-94 electronic warfare system – to other aircraft.

Lockheed says Project Missouri was led by Skunk Works development division, but was also “supported” by the USAF's Air Combat Command.

Northrop’s support for the fifth to fourth-generation demonstration did not come from the USAF directly, but from the Office of the Secretary of Defense. It was funded as a joint concept technology demonstration, with the goal of supporting both the USAF and the US Navy.

Although billed as “fifth to fourth”-generation networking systems, both the Lockheed and Northrop technologies fundamentally enable connectivity between fifth-generation aircraft, such as the F-22 and F-35.

F-22 F-35 - USAF

US Air Force

As currently designed, the F-22’s IFDL is unable to exchange data with the MADL on board the F-35. Both systems use unique waveforms with different frequencies and antennas.

That is one reason Northrop might choose to emphasise the dual-band antenna embedded in the Freedom 550 system. Officially, Honeywell’s antenna allows the Northrop radio to receive transmissions simultaneously from the F-22’s IFDL and the F-35’s MADL, translate both into Link 16 and pass them along to other aircraft.However, the same feature allows an F-35 transmission to be received by the Northrop radio, translated into the IFDL waveform and sent to an F-22, Northrop says.

But there is a potential downside. If a non-stealthy aircraft is used to translate messages being passed between two stealthy aircraft, it could compromise a mission that depends on evading radar. However, there could be ways to mitigate the problem, like using a stealthy intermediary – such as the Lockheed RQ-170 unmanned air vehicle, or a Freedom 550-equipped F-35 – to do the translations.

The goal of connecting the F-22 fleet to the airborne data network is not new. Besides the proposals to integrate TTNT and MADL, Northrop successfully demonstrated in 2008 that the F-22 could transmit a Link 16 message with IFDL components. However, Northrop officials acknowledge that was a one-off demonstration to simply prove the feasibility of the concept, and not an operational system.

The latest wave of flight demonstrations show that the F-22 can finally be connected – if funding is available to complete development and roll-out the technology to the fleet.

Source: FlightGlobal.com