From: maury_markowitz@hotmail.com   
      
   Alejandro Zuzek wrote:   
   > I know that a launch from the equator to a zero inclination orbit gets all   
   > of the advantage of the Earth rotation, but I was wondering if this   
   > advantage works the other way round too. In other words, does a reentering   
   > spacecraft from the due east equatorial orbit have significantly less   
   > demanding conditions than a spacecraft entering from a non-zero inclination   
   > orbit? Has this advantage ever been exploited? (The only spacecraft that I   
   > know of that reentered from an almost equatorial orbit was ESA's ARD, have   
   > there been others?)   
      
   The major advantage is that there is no "window". Since the spacecraft   
   orbit always crosses the launch point (or landing point), you have to   
   wait one orbit at most to land.   
      
   Contrast this with the Space Shuttle. After launch its orbit is tilted   
   to the Earth, so the Earth is spinning under it. After one 90 minute   
   orbit, the launch site has moved hundreds of miles to the west. To land   
   back where they started they have to wait, sometimes long periods, until   
   their orbit crosses their landing site. Although the site moves for a   
   zero inclination orbit as well, it moves toward you, not to the side.   
      
   In fact it is exactly this "drift" that caused the Shuttle to look the   
   way it does. Many early Shuttle designs were much smaller and used   
   small, straight wings that were only effective in the lower atmosphere   
   for landing. However when the Air Force agreed to support the project,   
   they demanded many things, one of them being the ability to abort back   
   to the launch site after a single orbit. Since their missions were   
   primarily polar, the "drift" would be up to 1000 miles, and thus the   
   Shuttle had to use the current delta-wing shape in order to dramatically   
   increase re-entry manuverability.   
      
   Maury   
      
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