Reference

Ley, Willy. Rockets, Missiles and Space Travel.
     Viking Press, New York, 1958.

Boeing.com Future X. April 14, 2004
     <http://www.boeing.com/defense-space/space/futurex/>

Wikipedia. The Free Encyclopedia. Space Shuttle program.
     April 14, 2004 <http://en.wikipedia.org/wiki/Space_shuttle/>

Starsem. The Soyuz Company. Introduction to Soyuz.
     April 14, 2004 <http://www.starsem.com/>

NASA. KSC Next Gen Site. Guide for the Design of Highly Reusable
     Space Transportation. April 13, 2004
     <http://science.ksc.nasa.gov/shuttle/nexgen/Guide_HRST_Design/rlvgide.htm>

Pictures Reference

NASA. Space Shuttle Columbia.
     <http://en.wikipedia.org/wiki/Image:Shuttle.jpg>

RSA. Russian/French Soyuz U - Fregat.
     <http://www.orbireport.com/Portraits/Soyuz_U-Fregat.jpg>

Boeing. Boeing X-38 project.
     <http://www.allstar.fiu.edu/aero/images/x-38.jpg>