bsk@portia.Stanford.EDU (Brian Keller) (09/18/90)
In article <15004@burdvax.PRC.Unisys.COM> techpubs@PRC.Unisys.COM (Technical Pub. Vince Short) writes: >In the STS-41 press kit, we find that: > >". . . After being deployed from Discovery . . . a two-stage Inertial >Upper Stage and a single-stage Payload Assist Module will boost Ulysses >on a trajectory that will take it to Jupiter in 16 months. . . ." > >This is a direct transfer orbit to Jupiter. > >My question: if this can be done for Ulysses (direct transfer orbit >to Jupiter), why couldn't it have been done for Gallileo which >was sent to Jupiter via a complex Venus-Earth-Earth gravity assist orbit. > >Gallileo was launched via Atlantis during mission STS-34 in October 1989. >However, it only used an Inertial Upper Stage (IUS) without the "assist" >of a Payload Assist Module (PAM) after the IUS burns. > >Why no PAM on Gallileo? Is Gallileo so much heavier than Ulysses? Anyone >have any numbers (masses, delta v's, etc) for the craft and their orbits? >Was there just no way to attach a PAM between the IUS and Gallileo? >Or what? > > Yes, Galileo IS much heavier than Ulysses, by a factor of 2 or 3, as far as I can remember (I wish I had my references with me know). As a result, the IUS does not have enough poop to get Galileo on a direct trajectory to Jupiter. When the Centaur was going to be used (the plan before Challenger), both were going to be launched direct within about a month of each other. However, after Challenger, there was a crisis about whether the Galileo mission was even feasible with any of the existing upper stages that were "allowed". The only possibilities included using gravity assists from Venus and Earth. I used to work at JPL and my former supervisor found the first such trajectory within 24 hours of a major briefing for NASA as to whether Galileo could still fly. Brian Keller bsk@tunguska.stanford.edu