Key point: While the Su-57 is fast, it does represent a step backward in speed compared to the MiG-31.

During the Cold War, the Soviet Union’ s Air Defense Forces (VPVO) needed a series of heavy interceptors to patrol its massive borders. Most regular “light” fighters like the early MiGs were not up to the task, as they lacked the range and speed to intercept to rapidly climb and intercept supersonic American bombers, who were expected to zoom over the Arctic to drop bombs on the Soviet Union.

As a result, a specialized class of aircraft was created for this purpose. The first was the Tupolev Tu-28 and Tu-128. These aircraft would lay the template for later interceptors: they were large for good endurance, fast, and were armed solely with missiles.

This design was obsolete from the time it entered service in the 1960s, as the B-58 Hustler that was in service at the time could outpace it. However, the MiG-25 “Foxbat” was also in development at the time. This aircraft would go on to become the definitive interceptor of the VPVO.

Blisteringly fast and armed with the massive R-40 air-to-air missiles, the Foxbat stood ready to defend the Soviet Union’s borders against all threats. Its airframe also saw adaptation into more tactical roles, photo reconnaissance and strike versions of the MiG-25 were created for the Soviet Air Force (VVS).

In the 1980s, the MiG-25 was followed up by the MiG-31, which added in a second weapons systems officer on all models and increased the flight performance, radar and weapons of the craft. Early versions also featured a cannon, but this was quickly deleted once it was determined that such extras were not necessary on a pure interceptor.

Nowadays the MiG-31 is the standard long range interceptor of the Russian Air Force (the VPVO was merged with the VVS in the 1990s) and is expected to serve into the 2030s. A “mid-life upgrade” of the MiG-31 is currently being procured: the MiG-31BSM. This modification integrates many new strike weapons onto the MiG-31 and modernizes most systems. The MiG-31 was also chosen as the primary carrier aircraft for the Kinzhal hypersonic missile.

But in August 2018, Russian outlets announced that experimental design work was beginning on a next generation pure interceptor that is meant to replace the MiG-31. Following the naming convention of Russia’s other next generation aircraft projects (PAK (XX)), the new interceptor project is called PAK DP, or Prospective Aviation Complex Long-range Interceptor.

The continuation of a line of dedicated interceptors is interesting because the existing PAK-FA/Su-57 fighter in many ways could fulfill the same role as the MiG-31. It has a highly advanced radar, it can supercruise (maintain Mach 1+ flight without the use of afterburners), and it could be armed with long range air-to-air missiles.

While the range is less than a MiG-31, air-to-air refueling can make up the gap. But since the capabilities as they stand are so similar, why the need for a separate airframe? Sukhoi fighters have also served in the interceptor role before, the Su-27P variant of the Flanker was meant explicitly for the VPVO. There are a couple reasons why the Russian government still considers the PAK DP to be necessary.

The first is that the PAK DP might build off the multirole nature of the earlier MiG-31 and MiG-25 conversions. An aircraft close to the original conception of the F-111 could be in the cards for Russia in the PAK DP: something that can carry a ton of long-range missiles and also perform strike with a wide range of munitions (including hypersonic ones)while moving very fast.

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Another possible reason is that Russia wishes to keep the heritage of MiG alive within United Aircraft Corporation (UAC). Since Sukhoi has done the majority of the design work and has had its name attached to the PAK FA (in the Su-57 designation), MiG needs a next generation project of their own to work on. The MiG-35, while advanced, is still not of the PAK family of next-generation craft and MiG not have an aircraft to work on in the future.

The last reason is that the VVS might want to future proof their interceptor force against future developments in UAV technology. While the PAK FA is fast, it does represent a step backward in speed compared to the MiG-31. While the SR-71 Blackbird is retired, UAVs incorporating some of its technology may come online in the future. Russia might need a plane that can really push the limits of speed to intercept them and keep its airspace safe.

Charlie Gao studied political and computer science at Grinnell College and is a frequent commentator on defense and national-security issues. This first appeared in August 2018.

Image: Wikipedia.