November 25, 2013
Credit: Northrop Grumman Concept
Lockheed Martin has labeled the hypersonic technology to be used in the proposed SR-72 Mach 6 aircraft as the “new stealth.” It is really the old stealth, and it points to a classic example of how almost every military and political leader in Western defense fell in line behind a technical miscalculation.
The story of the SR-72's predecessor, the A-12 Oxcart, is endlessly fascinating. One of its most important and long-concealed aspects was the critical role of stealth. The Skunk Works' Texas rival, Bob Widmer's team at General Dynamics, came close to beating Lockheed for the CIA's business with their stealthy Kingfish, which looked weirdly like the much later F-117. Skunk Works head Kelly Johnson, who had been a staunch skeptic when it came to “radar camouflage,” hurriedly reshaped the Lockheed contender with chines, canted tails and radar-absorbing structures.
Behind both designs was a theory that reduced radar cross-section (RCS) and high speed would combine to defeat surface-to-air missile (SAM) systems. North American was even looking at ways of reducing the head-on RCS of the B-70 Valkyrie heavy bomber.
None of this cut any ice with Robert McNamara, Kennedy's defense secretary. His “whiz-kid” operations analysts believed the Soviet Union would quickly develop bigger SAMs and radars that would wipe out the advantages of height and speed. The B-70 was canceled, and a nuclear-strike version of the A-12 was tolerated only when it was turned into the experimental YF-12 and unarmed SR-71. McNamara's favorite combat aircraft, the F-111, was designed around the ability to fly at Mach 1.2 at low altitude, and that was the only Pentagon-approved formula for a follow-on bomber study that would lead to the B-1.
The problem with McNamara's orthodoxy was that it was wrong. The S-200 SAM and MiG-25 interceptor that the Soviets designed to shoot down the A-12 could not alter the laws of physics. At high altitude, it takes wing area to intercept even a not-very-agile target, and it takes a lot of propellant to loft that big, draggy kill vehicle before the Mach 3 intruder turns the intercept into a tail-chase that the rocket loses.
Johnson's successor, Ben Rich, estimated the S-200 could down an SR-71 only if the warhead was of the instant-sunshine variety. In practice, nobody ever hit a Blackbird, while McNamara's low-fast penetrators proved vulnerable to guns, pelicans and attempts to tie the record for minimum altitude.
The U.S. Air Force dusted off the “high-fast sanctuary” in 1982 in defining the Advanced Tactical Fighter, the program that led to the Lockheed Martin F-22. ATF was intended to cruise at Mach 1.6 and pull 6g at supersonic speed in burner, all at 60-65,000 ft.
The original ATF requirements balanced stealth against speed, height and agility. All-aspect stealth was added to the menu after Lockheed and Northrop promised the Pentagon that the price in weight, money or risk would be small. The USAF would be in better shape today if they had been right. If you want to see the original requirements in action, look at the Chengdu J-20 and Sukhoi T-50.