Actually, that's NOT true. One of the bizarre ironies of the Galileo Saga (which is definitely worthy of a book; it took up literally half of my entire life) is that, if it hadn't been for every single one of the delays -- including the one caused by the Challenger tragedy -- Galileo would have failed completely before even reaching Jupiter, and it wouldn't even have been America's fault!
West Germany's Messerschmidt was assigned the job of building Galileo's main engine and maneuvering thrusters. They used the same thrusters on West Germany's first direct-broadcast comsat, TVSat-1, launched in early 1987. The satellite immediately became useless for its purpose because one of the technicians had failed to take all the pre-launch retention latches out of one of the solar panels and it wouldn't unfold, reducing the satellite's power by half -- but they then decided to use it for engineering tests. Lo and behold, within just a few months the attitude thrusters all started to burn out; it turned out that Messerschmidt had made a serious design error and not tested them enough to catch it. Galileo's thrusters would similarly have burned out -- or exploded -- within a short time of launch. One JPL engineer told Aviation Week, "We would have tried to find a work-around, but I doubt we could have done it." NASA and Messerschmidt then began a frenzied program to redesign, retest and reinstall new thrusters before Galileo's late 1989 launch; they made it with just a few months to spare.
So -- notwithstanding the fact that the Challenger accident was also indrectly responsible for jamming Galileo's high-gain dish -- if it hadn't been for that tragedy and all the previous years of repeated delays, the mission would have been TOTALLY lost and had to be reflown.
QUOTE (edstrick @ Feb 14 2006, 10:02 AM)
A mission that I'm wondering whether it was proposed and how much it might have been studied is a Mariner 9+ Venus orbiter. Take the Mariner 9 design, modify it for Venus thermal and communications requirments, maybe take out the telephoto camera, add a near-infrared spectrometer and/or radar altimeter and you'd have had a hell of a mission.
Mariner 10 ended up flying as the first Mercury recon with a very useful Venus flyby with non-optimum geometry and instruments for Venus. Pioneer Venus Orbiter did a lot with a smaller spacecraft, though a terrible scientific loss was the failure of the infrared atmosphere radiometer which was one fine instrument that only lasted some 1/5 of the primary mission.
They could have done that very easily indeed. Aviation Week, at the time, mentioned that a Venus orbiter was one of several alternative uses being considered for the Mariner 10 backup spacecraft. (Another was having it make a flyby of Comet Encke, albeit at a rather distant several thousand km because of the difficulty of installing dust shielding on it.) Needless to say, they ended up using it for nothing at all, and so it now hangs in solitary glory on the wall of the Air and Space Museum, near Voyager 3 and Viking Lander 3. (When I visited the Museum in 1983, I ground my teeth at that particular part of the displays.) I suppose it could indeed have been used to fly the Pioneer 12 mission at lower total cost -- although, since it wasn't spin-stabilized, its total observation time would have been a lot less.