Full color publication. This document has been produced and updated over a 21-year period. It is intended to be a handy reference document, basically one page per flight, and care has been exercised to make it as error-free as possible. This document is basically "as flown" data and has been compiled from many sources including flight logs, flight rules, flight anomaly logs, mod flight descent summary, post flight analysis of mps propellants, FDRD, FRD, SODB, and the MER shuttle flight data and inflight anomaly list. Orbit distance traveled is taken from the PAO mission statistics.

The space shuttle is a unique national resource. One of only two operating vehicles that carries humans into space, the space shuttle functions as a scientific laboratory and as a base for construction, repair, and salvage missions in low Earth orbit. It is also a heavy-lift launch vehicle (able to deliver more than 18,000 kg of payload to low Earth orbit) and the only current means of returning large payloads to Earth. Designed in the 1970s, the shuttle has frequently been upgraded to improve safety, cut operational costs, and add capability. Additional upgrades have been proposed-and some are under way-to combat obsolescence, further reduce operational costs, improve safety, and increase the ability of the National Aeronautics and Space Administration (NASA) to support the space station and other missions. In May 1998, NASA asked the National Research Council (NRC) to examine the agency's plans for further upgrades to the space shuttle system. The NRC was asked to assess NASA's method for evaluating and selecting upgrades and to conduct a top-level technical assessment of proposed upgrades.

The Galileo mission to Jupiter explored an exciting new frontier, had a major impact on planetary science, and provided invaluable lessons for the design of spacecraft. This mission amassed so many scientific firsts and key discoveries that it can truly be called one of the most impressive feats of exploration of the 20th century. In the words of John Casani, the original project manager of the mission, "Galileo was a way of demonstrating . . . just what U.S. technology was capable of doing." An engineer on the Galileo team expressed more personal sentiments when she said, "I had never been a part of something with such great scope . . . . To know that the whole world was watching and hoping with us that this would work. We were doing something for all mankind." When Galileo lifted off from Kennedy Space Center on 18 October 1989, it began an interplanetary voyage that took it to Venus, to two asteroids, back to Earth, and finally on to Jupiter. The craft's instruments studied Jupiter's enormous magnetosphere and its belts of intense radiation. The spacecraft also sent off a planetary probe that accomplished the most difficult atmospheric entry ever attempted. After this, the craft spent years visiting Jupiter's moons and delving into their structures and properties. This book attempts to convey the creativity, leadership, and vision that were necessary for the mission's success. It is a book about dedicated people and their scientific and engineering achievements. The Galileo mission faced many significant problems. Some of the most brilliant accomplishments and "work-arounds" of the Galileo staff occurred precisely when these challenges arose. Throughout the mission, engineers and scientists found ways to keep the spacecraft operational from a distance of nearly half a billion miles, enabling one of the most impressive voyages of scientific discovery.

As this excellent book demonstrates, the study of comets has now reached the fas cinating stage where we understand comets in general simple tenns while, at the same time, we are uncertain about practically all the details of cometary nature, structure, processes, and origin. In every aspect, even including dynamics, a choice among several or many competing theories is made impossible simply by the lack of detailed knowledge. The space missions, snapshot studies of two comets, partic ularly the one that immortalizes the name of Sir Edmund Halley, have produced a huge mass of valuable new infonnation and a number of surprises. Nonetheless, we face the tantalizing realization that we have obtained only a fleeting glance at two of perhaps a hundred billion (lOll) or more comets with possibly differing natures, origins, and physical histories. To my personal satisfaction, comets seem to have discrete nuclei made up of dirty snowballs, as I concluded four decades ago, but perhaps they are more like frozen rubbish piles.