ANALYSIS: Russian Su-57 Carrying External Missiles Compromises Its Stealth Capability – Why?

A video posted on Telegram on Oct. 19 by the pro-Russian milblogger FighterBomber, who is said to have a close relationship with Moscow’s aerospace forces, showed a Sukhoi Su-57 (NATO: Felon) allegedly flying close to the front line carrying two KH-59M2 cruise missiles on the outside.

The Su-57, like other stealth aircraft, is designed to carry its weapons internally to minimize the fighter’s radar cross section (RCS) and launch stealthy missiles or glide bombs. Carrying missiles on external weapons pylons compromises the aircraft’s reduced radar reflectivity and, therefore, its ability to operate in a high-threat environment.

The question is – why?

The Su-57 has two internal missile bays for which a modified version of the KH-59, the Kh-59Mk2, has been produced. It is made from stealthy materials, was designed to fit into the aircraft, and is, therefore considerably smaller than the original which results in a lower maximum range and a lighter, less lethal warhead. By the same token the original model is too big to fit inside the internal bomb bay.

It could be that the Russian forces simply have a shortage of the internally carried, far more expensive missiles, but still want to deploy the Felon, for which external hardpoints are available.

Russian armed forces may believe they have sufficient air superiority over Ukraine which has fewer radars, fighter aircraft, and surface-to-air missiles that would threaten conventional non-stealthy fighters. In such an operational setting, the carriage of the larger, more capable KH-59M2s would make logical sense.

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It could simply be a choice of combining a lower-cost weapon with greater lethality. Nevertheless, it is still somewhat of a gamble. Launching non-stealthy weapons from a stealth fighter would increase the chance of the aircraft being detected and engaged as well as negating the whole purpose of the stealth design which is to allow it to penetrate enemy airspace and launch its weapons untargeted and perhaps entirely undetected.

The Su-57 first flew in 2010, but serious development of stealthy weapons designed for internal carriage in the aircraft only began five or six years ago with the Kh-59Mk2 having only been recently developed.

Another explanation is that the carrying of external missiles alters is a deliberate attempt by Russian forces to mask the stealth signature of the Su-57 making it more difficult to record its actual radar profile in Western recognition databases and to deceive a future enemy’s radar.

In the same way, the US F-22 Raptor and F-35 Lightning stealth fighters feature systems that allow them to selectively change or control their radar cross sections (RCS) during peacetime by altering the way radar energy is absorbed or reflected by the aircraft.

However, once the weapons are released in a combat scenario, the Su-57 would revert to its native RCS, unless they are counting on only presenting a tail aspect radar picture as they leave the battlespace. The Russians may believe this could skew data gathered by any Western radars watching their ingress and egress, especially since RCS is heavily dependent on airframe angles, both horizontally and vertically.

Moscow may also think external carriage of the Kh-59M2 missiles would sufficiently affect the RCS of the Su-57 confusing Ukrainian ground radars and US/NATO airborne radars on AWACS aircraft that are known to monitor airspace over Ukraine’s battlefield, in the long if not the immediate term. This could be used to mask the future presence of Su-57s being used in combat by the Kremlin's forces.

There have been several reports of Su-57 attacks using Kh-59Mk2 missiles against Ukrainian targets, including the April hit on the 245-meter (804-foot) Kharkiv TV tower and the Oct. 4, attack on an infrastructure facility in Mykolaiv.