On October 20, the account @ClashReport shared on the X platform a still image from a video showing a Su-57 Felon, Russia's most advanced fifth-generation fighter, equipped with two Kh-59 cruise missiles (NATO designation AS-13 Kingbolt).

These missiles are believed to be the Kh-59M2A variant, an improved version for precision strikes against ground targets. The images quickly went viral and attracted much attention in the international community, sparking many discussions about the compatibility between the Su-57's stealth technology and these weapons systems.

Russian Su-57 fighter jet spotted flying with two Kh-59 air-launched cruise missiles (Photo source: X Channel @ClashReport/ Vitaly Kuzmin)

The Su-57, developed by Russia under the PAK FA program to replace the MiG-29 and Su-27, is one of the fighters designed to compete with modern models such as the US F-22 and F-35. It stands out for its stealth, super-maneuverability and super-cruise capabilities.

The aircraft is equipped with two Saturn AL-41F1 engines, allowing it to reach a maximum speed of Mach 2 and maintain supersonic cruise without afterburners. The Su-57's stealth features are based on an integrated wing-body design, angular vertical stabilizers, composite materials and radar-absorbent materials, which significantly reduce the radar cross section (RCS). The Su-57's advanced AESA radar system is also highly regarded for its ability to detect and engage multiple targets simultaneously.

In terms of weapons, the Su-57 is capable of carrying a variety of air-to-air and air-to-ground missiles in internal bays, such as the R-77M, R-74M2, Kh-38M, and Kh-35U. For missions less focused on stealth, the aircraft can also be equipped with external hardpoints to carry weapons such as 30mm autocannons. However, the use of external hardpoints could compromise the Su-57's stealth capabilities, which became a concern when Kh-59 missiles were seen on the aircraft in the viral images.

The Kh-59, a cruise missile developed since the 1980s by Russia's Tactical Missiles Corporation, has undergone many improvements with variants such as the Kh-59M and Kh-59MK2, increasing its range and improving its guidance capabilities.

This missile can attack both land and sea targets with high accuracy thanks to the inertial guidance system (INS) and the electro-optical or TV guidance head. Equipped with a solid-fuel propulsion engine and a jet engine, the Kh-59 can reach speeds of 900 to 1,050 km/h, with a range of 200 to 285 km. In particular, the ability to fly at low altitudes helps the missile avoid enemy radar systems.

While the Kh-59 is capable of precision strikes, it is not designed to reduce the radar cross-section of more modern stealth munitions, such as the Kh-69. As such, using the Kh-59 on the Su-57 with external pylons could reduce the aircraft's stealth effectiveness, making it more vulnerable to enemy radars during ground attack missions.

Images of the Su-57 carrying the Kh-59, if authentic, would partly reflect the limitations of Russia’s weapons integration capabilities for stealth aircraft. While the Su-57 is designed with superior stealth capabilities, carrying legacy weapons systems like the Kh-59 could significantly reduce this capability, especially in combat situations that require maximum stealth. This also raises questions about the effectiveness of the Su-57 in modern combat operations where stealth is important.

The imagery also suggests that Russia may still rely on older weapons systems for certain missions, despite the development of new technologies. This may be due to technical challenges or limitations in mass-producing modern stealth munitions. Given Russia’s many challenges on the battlefield, the use of the Kh-59 missile on the Su-57 may be a strategic move to ensure operational flexibility, but at the same time, it may also reduce some of the stealth capabilities that the aircraft was designed to achieve.