11 February 2015

The Corvus Missile- Laying the Foundation for US Anti-Radiation Missiles

Wind tunnel model of the Corvus missile
In the Second World War, the Radioplane Company had built thousands of remote controlled drones for target practice. In the late 1940s, Radioplane was asked by the USAF for a jet-powered drone for target practice and in 1950 first flew the YQ-1 which was powered by a pulse jet. The drone only had a flight time of about 60 minutes which wasn't terribly useful for the USAF's needs. One drone was converted to use a small Continental J69 turbojet but by the time this version had flown in 1953, the USAF had settled on the Ryan Firebee series of drones for its needs. Radioplane's work transferred over to GAM-67 Crossbow missile program that started in 1953 to meet a USAF need for an anti-radiation missile for the Boeing B-50 Superfortress and B-47 Stratojet bombers. The Crossbow would have been the world's first missile designed to kill radars and was to have had a lightweight 10-kiloton nuclear warhead. A Stratojet could carry four Crossbows under its wings. The first successful guided flight took place in 1957 but the program was soon canceled due to technical difficulties. At the same time the Crossbow flight test program was gearing up, the Navy decided they wanted their own anti-radiation missile and in 1955 issued a requirement for a rocket-powered stand-off missile for its carrier attack aircraft. That missile was designated the ASM-N-8 Raven, but a parallel project going on at the time with the Navy duplicated the Raven's role, so the Raven program was canceled early on and efforts shifted (along with the ASM-N-8 designation) to what was called the Corvus missile. 

In January 1957, development of the Corvus missile was awarded to Dallas-based Temco Aircraft. Temco (Texas Engineering and Manufacturing) was founded in 1952 by Robert McCullough who was the plant manager of North American Aviation's plant in Grand Prairie next to NAS Dallas. McCullough and his group took over the plant from North American under the Temco name and kept it open doing subcontracting work for other aircraft manufacturers. Soon Temco got into electronics and missile guidance systems and by the time of the Corvus contract, nearly half of Temco's revenue came from their missile guidance work. The Corvus award was a boost to the company that they were experienced enough to take on a complete weapons system like the Corvus on their own.

XLR-48 engine on display at the Smithsonian
The Corvus was a big missile. It was 16 feet in length and weighed about 1750 lbs. It had delta wings to extend its range and cruciform tail surfaces set at 45 degrees from the delta wing. Instead of a jet engine as was used on the Crossbow, the Reaction Motors subsidiary of the Thiokol Corporation developed the XLR-48 Patriot pre-packaged liquid fuel rocket motor. Reaction Motors was already well established making rocket engines for the X-plane programs and to overcome the Navy's hesitation about having to store liquid rocket fuels aboard the carrier, the XLR-48 was pre-packaged with storable propellants so the missiles would never have to be fueled. This was a Reaction Motors innovation and for the Corvus, the XLR-48 offered greater thrust over a longer period of time than a solid rocket motor sized for the Corvus airframe. The propellants were hypergolic, meaning they ignited on contact which resulted in a surprisingly simple rocket motor. 

Drawing of an A4D Skyhawk with two Corvus missiles
The Corvus could be armed with either a conventional warhead or a 10-kiloton nuclear warhead very similar to what was planned for the Crossbow missile. Being rocket-powered, the Corvus was a lot faster than the jet-powered Crossbow, flying out at Mach 3 on a ballistic trajectory to 85,000 feet. The seeker head was designed by another Dallas-based electronics firm that would itself soon become famous in electronics, Texas Instruments. The seeker would lock onto an enemy radar emitter. In this mode, the Corvus had a range of 170 miles. It also could lock onto a target that was illuminated by the launch aircraft in a semi-active homing mode against non-emitting targets, but in this attack mode the range was shorter at around 100 miles. A data link would have been used to guide the Corvus in semi-active homing mode until it picked up the radar returns from the target. 

Corvus missile being launched from an A3D Skywarrior
The first airborne launches of the Corvus took place from a Douglas A4D Skyhawk in July 1959 from NAS Point Mugu in California. About twenty missiles were built and the program had progressed to fully guided flights when it was abruptly canceled in August 1960. The Navy had decided that nuclear-tipped air-to-surface missiles didn't quite fit with its operational doctrines and the program was transferred to the USAF. Finding the Corvus redundant to its own AGM-28 Hound Dog missile program that had been awarded already to North American Aviation in 1957, the program was canceled in late 1960 despite the Corvus being significantly lighter than the Hound Dog.

The work wasn't all for naught, though. Texas Instruments, who designed and was tapped to produce the Corvus radar seeker guidance head, gained significant experience from the program and would go on to work with the US Navy on the AGM-45 Shrike became the first American anti-radiation missile to be fielded and was used in combat for the first time in the skies over Vietnam against SAM sites. Texas Instruments would then go on in 1974 to develop the successor to the Shrike that is still in use to day, the AGM-88 HARM (High Speed Anti-Radiation Missile). 

As for Temco, their work on the Corvus made them an attractive merger target. Just prior to the Corvus cancellation in 1960, Dallas businessman Richard Ling, head of Ling-Altec Electronics acquired Temco to form Ling-Temco and shortly thereafter gained controlling interest in Chance Vought Aircraft, the new company becoming Ling-Temco-Vought, or LTV. 

Source: Scooter: The Douglas A-4 Skyhawk Story by Tommy Thomason. Crecy Publishing, 2011, p79. Pushing the Envelope: The American Aircraft Industry by Donald M. Pattillo. University of Michigan Press, 2001, pp 241-242. Detecting and Classifying Low-Probability of Intercept Radar by Phillip E. Pace. Artech House, 2008, pp 554-555. DesignationSystems.Net. Photos: Wikipedia, National Air & Space Museum, NASA.

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