NASA began the Tier-1 process with a Notice of Intent in January 1987. The draft EIS was published in November 1987. The only in-depth comments received were from the Committee to Bridge the Gap, and they dealt with the need to flyby the Earth on a VEEGA trajectory. VEEGA Trajectory: Earth avoidance analysis The purpose of the upper stage booster is to provide enough kinetic energy to propel the spacecraft from the shuttle parking orbit into its proper interplanetary trajectory. The Galileo spacecraft weighs some 6000 lb, and is by far our most massive outer plant mission to date. The Centaur G-prime had the capability (C3 = 78 km2/s2) to place Galileo on a direct trajectory to Jupiter. The IUS, while much safer, is also much less energetic (C3 = 14 km2/s2). So, to gain the needed kinetic energy for cis-Jupiter injection, the Galileo spacecraft will swingby Venus, then swingby Earth twice. The trajectory is thus called the Venus-Earth-Earth gravity-assist or VEEGA trajectory. No combination of launch vehicles available to NASA could avoid the need for Earth gravity assist in propelling Galileo to Jupiter. Ulysses will gain the needed extra energy from a third stage, the PAM-S. The tiered approach allowed us to gauge public reaction to the VEEGA trajectory. As a result, the mission design section at Jet Propulsion Laboratory (JPL) performed a comprehensive Earth avoidance analysis. The exhaustive, peer-reviewed analysis shows that the chance of an inadvertent reentry is less than 5 E-7. In addition, mission operations procedures will further minimize the chances of a stray command or guidance error. There will be round-the-clock monitoring during the period of closest approach. With the results of the Earth avoidance analysis in hand, NASA completed the Tier-1 process in November 1988. Galileo Mission Tier-2 EIS The mission-specific EIS was timed to use the results of the final safety analysis report (FSAR) for the mission. So the amount of detailed safety and environmental data was unusual for an EIS. Again there is a conflict: if the EIS has been completed when starting a project, detailed data are unavailable. If done later in the project, there is a chance of having to abandon a project after substantial commitment of resources. It should also be recognized that an exhaustive safety analysis was performed for the Shuttle launch of Galileo. In the post-Challenger environment, the spotlight of attention focused on the Galileo launch safety analysis. The Galileo launch was rescheduled from May 1986 to October 1989. That time was used to make extensive improvement in analytical techniques (e.g. atmospheric dispersion) and to resolve previously controversial safety test data (e.g. ‘direct course’ and ‘project pyro’ explosion tests). While the EIS is not a decision document, it is intended to support decisionmaking. Therefore, it should be a thorough analysis of the expected and plausible consequences of alternatives. The challenge is how best to present the results of the analysis. In the case of Galileo, the only environmental impacts are associated with the launch, and the only radiological impacts occur if there is a launch accident. The ‘if means one must adopt a probabilistic approach. But how to characterize the distributions of possibilities? There are distributions of:
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