The HST Strategy Panel held four meetings between mid-August and mid-October 1990. At these meetings, a wide variety of options for correcting spherical aberration were identified and debated. This report presents the Panel's findings and recommendations. Problems included: (1) the optical problem and solution; (2) COSTAR; (3) pointing; (4) WFPC; (5) servicing mission; (6) recommended strategy; and (7) fresh reasons to commit to the HST.

"Exploring the unknown" is a multi-volume series containing a selection of key documents in the history of the U.S. civil space program. Volume V, focusing on the exploration of space by robotic spacecraft that have significantly altered our perspectives on the cosmos, prints 121 key documents on the history of space science, planetary exploration of the solar system, and space astrophysics, edited for ease of use. Many of these documents are published here for the first time. Each is introduced by a headnote providing context, bibliographical information, and background information necessary to understanding the document. This documentary history is an essential reference for anyone interested in the history of the U.S. civil space program and its development over time. It will serve as a valuable source both for students and scholars. Additional volumes will appear later that trace space science and the programmatic developments in the history of the U.S. exploration of space.

In this book are reported the main results presented at the "Fourth International Workshop on Data Analysis in Astronomy", held at the Ettore Majorana Center for Scientific Culture, Erice, Sicily, Italy, on April 12-19, 1991. The Workshop was preceded by three workshops on the same subject held in Erice in 1984, 1986 and 1988. The frrst workshop (Erice 1984) was dominated by presentations of "Systems for Data Analysis"; the main systems proposed were MIDAS, AlPS, RIAIP, and SAIA. Methodologies and image analysis topics were also presented with the emphasis on cluster analysis, multivariate analysis, bootstrap methods, time analysis, periodicity, 2D photometry, spectrometry, and data compression. A general presentation on "Parallel Processing" was made which encompassed new architectures, data structures and languages. The second workshop (Erice 1986) reviewed the "Data Handling Systems" planned for large major satellites and ground experiments (VLA, HST, ROSAT, COMPASS-COMPTEL). Data analysis methods applied to physical interpretation were mainly considered (cluster photometry, astronomical optical data compression, cluster analysis for pulsar light curves, coded aperture imaging). New parallel and vectorial machines were presented (cellular machines, PAPIA-machine, MPP-machine, vector computers in astronomy). Contributions in the field of artificial intelligence and planned applications to astronomy were also considered (expert systems, artificial intelligence in computer vision).