The Aerospace Plane

The idea has been around for ever.  I have a beautifully illustrated children's book from 1951 with a drawing of such a machine.  Basically a high performance aircraft that would use wings and jet engines to lift an orbiter space craft high and fast.  It would be reusable (you fly it back and land it after launching the orbiter) and hence lower cost than  a throwaway booster like Atlas.    
  Attractive as the idea is, so far nobody has ever built one.  There are five NASA design studies, the earliest going back to 1986.  Since none of them ever flew, it's fair to say that the concept becomes less attractive when you actually have to build and fly one. 
  Anyhow, hope springs eternal and NASA is going to try again.  This time with a rocket powered craft dubbed XS-1.  Design goal is to loft a 3000-5000 pound satellite into low earth orbit for $5 million or less.  NASA is talking about $3-4 million study contracts early next year, with a $140 million "build-a-flying prototype"  contract  in 2015.  XS-1 is supposed to reach Mach 10 (roughly half orbital velocity).  Gross takeoff weight might be 224,000 pounds.  That's airliner weight.   Presumably  XS-1 burns all its rocket fuel on the way up and then glides back to a dead stick landing, the way the shuttle used to do.