Preparation To enhance reliability and reduce costs, the project engineers decided to switch from a pressurized atmospheric probe to a vented one, so the pressure inside the probe would be the same as that outside, thus extending its lifetime in Jupiter's atmosphere, but this added to its weight. Another was added in structural changes to improve reliability. This required additional fuel in the IUS, but the three-stage IUS was itself overweight with respect to its design specifications, by about . Lifting Galileo and the three-stage IUS required a special lightweight version of the Space Shuttle external tank, the Space Shuttle orbiter stripped of all non-essential equipment, and the Space Shuttle main engines (SSME) running at full power level—109 percent of their rated power level. Running at this power level necessitated the development of a more elaborate engine cooling system. Concerns were raised over whether the engines could be run at 109 percent by the launch date, so a gravity-assist maneuver using Mars was substituted for a direct flight.
Preparation To enhance reliability and reduce costs the project engineers decided to switch from a pressurized atmospheric probe to a vented one so the pressure inside the probe would be the same as that outside thus extending its lifetime in Jupiter's atmosphere but this added to its weight Another was added in structural changes to improve reliability This required additional fuel in the IUS but the three-stage IUS was itself overweight with respect to its design specifications by about  Lifting Galileo and the three-stage IUS required a special lightweight version of the Space Shuttle external tank the Space Shuttle orbiter stripped of all non-essential equipment and the Space Shuttle main engines (SSME) running at full power level—109 percent of their rated power level Running at this power level necessitated the development of a more elaborate engine cooling system Concerns were raised over whether the engines could be run at 109 percent by the launch date so a gravity-assist maneuver using Mars was substituted for a direct flight