ST401385@BROWNVM.BITNET (02/10/86)
>[in response to a question as to why we don't head out >to Uranus again as soon as possible] >>because the relative positioning of Jupiter-Saturn-Uranus, >>that allowed Voyager to make it to Uranus in 'only' 8.5 years, >>only happens once in *175* years... >I believe that refers to the Jupiter-Saturn-Uranus-Neptune configuration. ...surely a single slingshot Earth to Jupiter Uranus does not have a rare launch window ... The Earth-Jupiter-Uranus alignment condition is not all that common. Jupiter-Uranus alignment comes slightly less than once every Jupiter year (12 years). Only a portion of these will come at a time favorable to Earth-Jupiter alignment. Further, it was my understanding that Voyager needed gravity slings from both Jupiter AND Saturn to get to the outer planets. This is considerably more rare than just the Jupiter-Uranus alignment. Saturn-Uranus alignments are slightly less often than once every Saturn year, 45 years, and not very many of these will occur in synchronism with the Jupiter-Saturn alignment *and* the Earth Jupiter alignment. Only the fact that there is some amount of midcourse alignment allowing less-than-completely-perfect alignment makes the alignment condition as *often* as once every 175 years. --Geoffrey A. Landis