The United States has made National Missile Defense a top priority.  Billions of dollars have been spent on various anti-missile concepts, and the most promising is intercepting the missile head-on.  This requires that a Mach 5 intercepting missile is directed toward a Mach 5 ICBM by long-range ground-based radar.  As the two objects close at Mach 10, the intercepting missile must detect the infra-red signature of the oncoming missile and adjust perfectly for a collision.  This remarkable feat has been described as "hitting a bullet with a bullet".  In reality, a bullet travels only about Mach 2, so this is twice as difficult.  In addition, each interceptor missile is a multi-stage rocket that cost millions of dollars.  As a result, testing is expected to continue over the next ten years to see if this complex system will work.yf935az.jpg

     An anti-missile defense concept that has not been considered can use technology developed forty years ago.  A Sky Ramp can launch a ramjet-powered military aircraft to act as an interceptor.  This can be a manned or unmanned aircraft similar to the YF-12 Interceptor, which was successfully tested in the 1960s (left).  Aircraft on standby in Alaska, Canada, or Greenland could be launched within minutes and fly at Mach 5 to intercept ICBMs, supersonic bombers, or cruise missiles approaching the USA.  Since ramjet-powered aircraft cannot fly outside the atmosphere, they are limited to 100,000 feet, or 20 miles high.  ICBMs fly ~200 miles high, so an Interceptor would fire long-range air-to-air missiles upward to hit one.  Another advantage is that a reusable "Interceptor" will not violate the anti-ABM treaty, so it solves diplomatic problems with the Russians and NATO allies. 

     This is not a theory, the YF-12 once fired an AM-47 Mach 5 missile (right) with a range of 140 miles at 80,000 feet while flying Mach 3.2.   An interceptor aircraft provides many advantages over an interceptor missile.  It can change course or turn back as suspected targets are reclassified as decoys or space junk.  It can fly an arc to intercept at a 90 degree angle so the closure rate is Mach 5 instead of Mach 10.  If the interceptor can fly faster than an ICBM, it may be able to shadow a missile from below.  It can carry onboard radar to locate the missile and guide missiles toward the target.  

      The US already uses several types of air-to-air missiles with a range in excess of 100 miles at sea level.  If fired upward at 80,000 feet, they would encounter no air resistance, so their range and velocity will more than double.  However, their guidance fins would fail, so they will need tiny guidance jets like those used by today's NMD interceptors, and by TOW anti-tank missiles.  This allows a ramjet-powered interceptor to fire several types of low-cost missiles at a target (and decoys) to ensure destruction.  It can fire a missile with a internal radar seeker (like AMRAAM), a missile with infrared tracking (like Sidewinder), or a missile guided by the interceptor's radar, (like Phoenix).  The Air Force proved this possible when an F-15 fired an ASAT missile (left) to shoot down a satellite during a 1985 test. 

      With this many options, there is no doubt an interceptor can down one or more ICBMs, supersonic bombers, or low-flying supersonic cruise missiles.  The tactics will depend on its speed.  The  YF-12, which became the SR-71, had a maximum speed of Mach 3.2 with jet engines developed in the 1960s, although sustained speed was only around Mach 2.  Ramjets provide more speed since they are not restricted by the heat build-up of the spinning turbine.   The FY2009 U.S. Defense budget includes $750 million to build a Mach 5 prototype as an SR-71 successor, dubbed "Blackswift." (below)

      Since Sky Ramps are needed to launch ramjet-powered aircraft, the problem of recovery may arise if it lands at a conventional airstrip far from a Sky Ramp.  It if has swept wings like the B-1, it could spread its wings after a mission and glide great distances back home.  It may also have a small internal jet engine which pops out to help power it home.  Or, it may be designed so that ground crews can mount external jet turbine engines to fly home. This would allow it to operate from any airfield with jet turbine engines, albeit at much slower speeds than powered by its ramjet engines.  Ideally, the interceptor would be capable of single-orbit missions with ramjet engines  so it can glide home to its Sky Ramp launch site.

      A worldwide Mach 5 Reconnaissance-Interceptor-Bomber (RIB) aircraft is exactly what the U.S. Air Force is seeking for its "Aerospace Force".  Aside from its value as a missile and bomber interceptor, it could shoot down low orbit satellites.  A reconnaissance version can fill the role vacated by the retirement of the SR-71s.  Flying at Mach 5, it could over-fly any country and easily outrun any missile fired to shoot it down.  It could also load up with JDAM satellite guided bombs and drop them with impunity.  A bomber version could take off from Alaska, drop bombs in China, and land in England within three hours, or possibly circle the globe and return home within five hours.  In contrast, it took the subsonic B-2 44 hours of round-trip flying to strike Afghanistan, along with eight air refuelings.  In addition, the B-2 is only stealthy at night, and requires hours of skin repair work between missions.

       The US Air Force recognizes the need for a fast intercontinental aircraft for its "Global Reach" concept, and the obvious solution is  ramjet engines.  The major barrier has been a practical method of generating the near mach speed needed for ramjet ignition.  Sky ramps are the simple answer, and the assisted launch they provide greatly extends the range of the aircraft.  

2008 Sky Ramp Technology