Flag of the <a href="//commons.wikimedia.org/wiki/Space_Shuttle_Challenger" title="Space Shuttle Challenger">Space Shuttle Challenger</a>.  The shuttle flags are generally flown at the Kennedy Space Center while the orbiter was on the launch pad or on a mission, though possibly the practice did not start until after the Challenger disaster.  NASA did have a Challenger flag at the shuttle program retirement ceremony in 2011.<a rel="nofollow" class="external autonumber" href="http://www.mnn.com/earth-matters/space/stories/after-final-celebration-nasas-space-shuttle-program-officially-ends">[1]</a>
<a href="//commons.wikimedia.org/wiki/User:Clindberg" class="mw-redirect" title="User:Clindberg">Carl Lindberg</a>
Self-made, with all dimensions guesstimated from looking at images of shuttle flags.  Space Flight Awareness logo copied from <a href="//commons.wikimedia.org/wiki/File:NASA-SpaceFlightAwareness-Logo.svg" title="File:NASA-SpaceFlightAwareness-Logo.svg">File:NASA-SpaceFlightAwareness-Logo.svg</a>.  For example, <a rel="nofollow" class="external text" href="http://i.ebayimg.com/t/Authentic-NASA-SPACE-SHUTTLE-CHALLENGER-4X6-nylon-FLAG-/00/s/NzY4WDEwMjQ=/%24(KGrHqYOKioE5ezELRDtBO(uhb,Mc!~~60_57.JPG">this image</a> of a Challenger flag for sale on EBay shows the design.