Foreword

Abstract

In 1992 a small workshop in San Juan Capistrano marked the beginning of an innovation in planetary exploration, the Principal Investigator-led mission. NASA announced the establishment of a continuing “line item” in the budget for the development, launch and operation of missions led by a Principal Investigator from inside or outside NASA. These missions were to be less costly than flagship missions that addressed the major objectives of planetary exploration. They would be more focused, developed more quickly for flight, with a limited number of instruments and a limited number of investigators. They would ensure that the smaller but important objectives of the planetary program would be addressed. The first two missions were selected in a mode similar to the earlier selection process to get the program off to a quick start but soon a new process was established. The best mission or pair of missions was to be selected from a group of about thirty proposals. From this process arose missions approved to go to the Moon, bring back solar wind and comet samples, to excavate a crater on a comet, to orbit Mercury, to orbit main belt asteroids, and to identify Earth-like exoplanets.