>If this is true, micrometeorites could puncture the tank very easily, >because there is only one wall to puncture and it is very thin, so >outgassing of the remaining fuel could in turn explane why we observe so >many flash period accelerations of those rockets. > One more thing. The Centaur upperstage (as well as Delta's second stage) both perform collision avoidance and propellant depletion burns after payload sep. Of course, sometimes things go wrong, such as an old Pegasus hydrazine upperstage (HAPS) which prematurely shut down, leaving fuel in it's tank. Years later, there are dozens of Seesaters tracking multiple pieces of the upperstage now! ___________________________________________ John C. Broman, Jr. X-34 Lead Avionics Engineer Orbital Sciences Corporation stingray@wizard.net (home) jbrom@orbital.com (work) ___________________________________________