The companies have found a way to pair a conventional turbine jet engine, such as those in existing fighter aircraft, with a supersonic combustion ramjet— an engine that can operate effectively only if an aircraft is traveling at very high speeds.
The pairing—first, makes a hypersonic plane a practical possibility, but Lockheed still faces scores of technological and funding challenges before the so-called Son of Blackbird becomes a reality.
Turbine engines would accelerate the notional SR-72 up to about Mach 3, before the jet transitions to scramjet propulsion. As the aircraft transitions into full scramjet propulsion, the turbines are deactivated. The scramjet would then accelerate the aircraft up to a maximum speed of about Mach 6.
Unlike the previous generation SR-71s’ Pratt & Whitney J58 engines, which were a partial ramjet design, the new engine concept burns fuel at supersonic speeds—allowing it fly a lot faster. But it is also more technologically challenging.
While the prospective government customers would be the U.S. Air Force and DARPA, Lockheed does not yet have a customer for the effort.
Lockheed hopes to launch the flight demonstrator program in 2018. While the 2018 flight demonstrator is not currently funded and is more of a notional project at this time.
The prospective demonstrator would be about the same size as the company’s F-22 Raptor stealth fighter. Unlike the operational SR-72 concept, it would be a single-scramjet engine design. The demonstrator would take off and land just like any normal aircraft, but would be able to cruise at Mach 6 for several minutes. Lockheed hopes to fly the demonstrator in 2023.
The operational SR-72 would be a twin-scramjet design, which Lockheed hopes would become operational in 2030.
It could hit any target on any continent in less than an hour, it could be a prompt theatre-strike weapon with more than 1,000 nautical miles of penetration into denied airspace (when the range of the missile is added to that of the SR-72).
Stealth would be of limited value in an aircraft like the SR-72, given that radar absorbent materials would not survive the extreme temperatures. Moreover, the jet would have a huge infrared signature, which would negate most signature reduction measures. The aircraft might also leave a wake that might be tracked on radar—much like the SR-71.
Survivability would be achieved through a combination of speed, altitude and some limited signature reduction.
Lockheed has a lot of experience with high-speed stores separation, which it gained on the 1960s-era YF-12 interceptor program.
The SR-72 would have range comparable to its SR-71 forbear—3,200 nautical miles.
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