Lockheed Martin Corp., the world’s largest defense contractor, has unveiled plans for an unmanned successor to the famous SR-71 Blackbird spy plane.

The new twin-engine, hypersonic aircraft, known as SR-72 and nicknamed “Son of Blackbird,” will be designed to fly as fast as Mach 6. That’s six times the speed of sound — more than 3,500 miles per hour — and twice as fast as its predecessor.

Details of the jet were first reported last week by Aviation Week, a trade publication. The Bethesda, Md.-based company wants to fly a missile to demonstrate the technology as soon as 2018. An operational aircraft could be ready by 2030 for surveillance or strike missions.

“Hypersonic aircraft, coupled with hypersonic missiles, could penetrate denied airspace and strike at nearly any location across a continent in less than an hour,” Brad Leland, Lockheed’s program manager for hypersonics, wrote in a blog post.

“Speed is the next aviation advancement to counter emerging threats in the next several decades,” he added. “The technology would be a game-changer in theater, similar to how stealth is changing the battlespace today.”

Like its predecessor, the aircraft is being developed by the company’s Skunk Works advanced development programs facility in California.

The plane would use a two-phase propulsion system. A standard jet turbine would propel the plane as fast as Mach 3, then a ramjet would kick in and accelerate the craft to hypersonic speeds.

Lockheed has teamed with the engine manufacturer Aerojet Rocketdyne, part of Rancho Cordova, Calif.-based GenCorp Inc., to integrate an off-the-shelf turbine with a supersonic combustion ramjet air-breathing jet engine to power the aircraft from standstill to Mach 6.

Lockheed has experimented with hypersonic aircraft before.

The company’s Falcon Hypersonic Technology Vehicle 2, or HTV-2, an unmanned, arrowhead-shaped glider, crashed into the Pacific Ocean in 2011 after flying for more than nine minutes and reaching speeds of Mach 20. (A similar flight in 2010 also failed.)

The Defense Advanced Research Projects Agency, the Pentagon’s advanced technology laboratory, which funded the project, later concluded the HTV-2 aircraft went so fast that its exterior coatings peeled apart from the airframe, creating gaps that caused the vehicle to roll and ultimately break apart.

The SR-72 will draw on lessons learned from the HTV-2 project, but won’t push the hypersonic envelop as far.