29 March 2010

The legendary Russian rocket designer Sergei Korolev and his special design bureau (designated OKB-1) were given responsibility in the early 1950s to develop a practical tactical ballistic missile designated the R-11 that would better be known by its NATO code name, SS-1 "Scud". The first Scud-A/R-11 missiles were accepted for operational use by the Soviet Army in July 1955 but the early versions were cumbersome to set up and fire, requiring multiple vehicles for support and despite advances in technology was little more practical than the German V-2 rocket. As a result, few operational batteries of the early versions of the Scud-A/R-11 missiles were fielded in the 1950s.

Subsequent developments of the early Scud-A/R-11 missile led to the development of the Scud-B/R-17 which featured a whole host of improvements in design and use. A new tracked TEL (transporter-erector-launcher) vehicle simplified operational deployment and advances in construction and propulsion extended the Scud-B/R-17's range over the Scud-A/R-11 missile. In addition, the Scud-B/R-17 was nuclear-tipped along with the options for conventional or chemical warheads. Soviet Army formations that fielded the nuclear-tipped versions of the Scud-B/R-17 usually had one chemical warhead for every 25 nuclear warheads. To simplify the ballistics and guidance, each of the possible warhead options for the missile was standardized at 1 metric ton. The first Scud-B/R-17 missiles become operational in 1962.

Despite the improvements from the Scud-A/R-11 to the Scud-B/R-17, the missile remained relatively inaccurate which was more problematic when using a conventional or chemical warhead which required more precise targeting than a nuclear warhead. The Scud-A/R-11 had a CEP (circular error probable- a circle in which the warhead was expected to land 50% of the time) of 4 kilometers. The first Scud-B/R-17s cut the CEP down to 2 kilometers, eventually attaining a 1 kilometer CEP. But with a conventional warhead, a 1-km CEP was nearly unacceptable. With a move in the 1960s by both the United States and the Soviet Union towards a more "flexible" response in a nuclear crisis, the Soviet military leadership saw that there would be times that a non-nuclear/non-chemical Scud missile warhead would be more desirable to use.

In 1967 the Central Scientific Research Institute for Automation and Hydraulics in Moscow was tasked to develop a top-secret precision-guided version of the Scud-B/R-17. It was originally designated R-17VTO Aerofon and the Institute decided upon a very prescient form of guidance, optical comparison in which the missile would hit its target by comparing an image of the target with an image stored in its memory. In the late-1960s the development of the guidance proved impractical and the Aerofon project was reorganized in 1974 to take advantage of advances in digital computing. The new system relied on digital images and a computer library could be kept of possible targets. The first Aerofon optical guidance prototype was completed in 1975 and successfully tested pod-mounted under a Sukhoi Su-17 strike fighter.

In the United States we had a similar guidance system under development called "digital scene matching area correlation" (DSMAC). The idea in the US system was that DSMAC would be used on cruise missiles on the final run-in on the target after using TERCOM (terrain contour-matching) on the flight into the target vicinity. It's likely that the first Aerofon guidance package was similar to the first analog version of DSMAC tested here in the United States- a stored photographic negative of the target was compared with a photograph taken of the target area. It was a cumbersome system as tested with DSMAC and the first tests were performed with a Tomahawk cruise missile in 1978.

The Aerofon optical guidance system was air-tested in 1975 and flight tested on an actual Scud-B/R-17 missile in late 1979, the Aerofon hitting only a few meters from the designated target. This represented a massive leap in improvement over the 1-km CEP of the Scud-B/R-17 standard missile. The planned operational Aerofon would have had a CEP on the order of 20 meters.

Unlike the other variants of the Scud missile family where the whole missile impacted the target, the Aerofon variant had a warhead section that separated from the main body of the missile (the first Aerofon missiles, though, did not have a detachable warhead section). At the base of this warhead section were lattice-section steering vanes that folded out into the air stream, providing maneuvering capability to the Aerofon warhead. In the base of the warhead section was the batteries for the power supply and its associated electronics. The nose section was tipped with an optical seeker that updated the inertial guidance and accessed the onboard computer for optical comparison of the target. In between the guidance section at the nose and the power/steering section at the base was the warhead which took up the majority of the space.

The production version of the Aerofon was ready for deployment by 1989 but it never went into large scale production as it was superseded by two more advanced battlefield ballistic missiles- the OTR-21 Tochka (NATO code name SS-21 "Scarab") and the OTR-23 Oka (NATO code name SS-23 "Spider"). However, in the 1990s, the Aerofon was offered for export to existing customers of the Scud missile.

Source: Scud Ballistic Missile and Launch Systems 1955-2005, New Vanguard #120 by Steven J. Zaloga. Osprey Publishing, 2006, p1-19.

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