Payloads on hypersonic aircraft, whether they are weapons or sensors, could reach their destination within minutes, rather than hours, said Mark Lewis, former chief scientist of the Air Force and now director of the Science and Technology Institute at the Institute for Defense Analyses, a federally funded research-and-development center.  Hypersonic speed is generally defined as beginning at Mach 5, which is the point where aerodynamic heating caused by the speed of the vehicle cutting through the atmosphere becomes a factor.

The Air Force concluded its successful X-51 WaveRider program in 2013. The final test had the missile-like aircraft flying at Mach 5.1 for about 200 seconds.  Meanwhile, the Army is testing the advanced hypersonic weapon, a missile designed for vertical launch. It suffered a failed test seconds after takeoff in August 2014, but that was caused by a faulty booster, not the missile or hypersonic technology itself, Lewis noted….

Hypersonic technology could be seen as a follow-on to stealth, Lewis said. Even if an aircraft has that kind of technology, it doesn’t mean it is invisible, he said. Adversaries are growing better at spotting stealthy aircraft, he said. Speed might compensate for that, he said. “If I can fly really fast, it makes it harder to act against me. It doesn’t make it impossible. But it makes it harder.”

Top Air Force leaders are indicating that they want to move hypersonic technology to the next level.  Air Force Chief of Staff Gen. Mark Welsh and Secretary Deborah Lee James in the document “America’s Air Force: A Call to the Future,” said hypersonic development was number one on the service’s list of top five technology priorities.  [T]the Air Force sees hypersonic weapons as a potential means to break through anti-access/area-denied battlefields where adversaries have robust defenses….

The Air Force will team with the Defense Advanced Research Projects Agency on two new hypersonic programs, he said. The first will be a cruise missile called HAWC, the hypersonic air-breathing weapons concept. The other is called tactical boost glide, which will accelerate an aircraft to Mach 5 plus speeds, then let it glide to its target.

Similarly, space planes could deliver payloads in minutes. The reusable space plane concept has been proposed many times over the years, and received a new lease on life when DARPA awarded three contracts to Boeing, Masten Space Systems and Northrop Grumman to study the idea of a two-stage launch system that could rapidly place 3,000 to 5,000 pounds into orbit. The Air Force has never given up on that idea, as evidenced by the new DARPA initiative, Lewis said.  Space planes have been talked about for decades, Lewis said. There have been many starts and stops in developing the concept, he added.

NASA’s space shuttle was originally conceived as a vehicle that could rapidly lift payloads into space at low cost, and be flexible and responsive. It never lived up to that promise.

The DARPA experimental spaceplane (XS-1) program envisions a reusable aircraft that could be launched from a mobile platform, and return 10 times within 10 days. It would employ a reusable first stage that would fly to Mach 10 at a suborbital altitude. At that point, one or more expendable upper stages would separate and deploy a satellite into low-Earth orbit.  While a space plane in low-Earth orbit could potentially be used as a weapon, it would more likely be employed as a means to rapidly replace satellites that have been damaged in a space war, or to place sensors over regions where there are currently no assets, Lewis said….

Meanwhile, more akin to the space shuttle than the DARPA concept for the space plane, the Air Force continues to use the X-37B, a top-secret orbiter that also glides to Earth. One has been in orbit since October 2012. The Air Force has repeatedly denied that it has, or is intended to be, weaponized. What its exact mission is remains classified

Excerpts from Stew Magnuson, Hypersonic Weapons Can Defeat Distance, National Defense Magazine, Nov.  2014