Introduction T HE growing number of Space Shuttle missions has presented the aerospace community with an unprecedented body of data on the Shuttle environment itself, as well as new data on astrophysical domains far from the Earth. This paper focuses attention on selected Shuttle environmental phenomena that may impact plans for future observations from the Shuttle platform. In this review data from STS 2-4 which have recently become available will be compared and contrasted. These data have all been presented previously, although not largely in the open literature. Among the many environmental factors that will interest users of the Shuttle, three factors have been selected that must be reckoned with for a broad range of instruments and measurements:; gases, particulates, and vehicle glows. We leave aside other issues such as mechanical structure, vibroacoustics, thermal excursions, electromagnetic interference, and materials degradation; the first three of these appear to be well understood at this time, and the last two are active research 'areas. Gases, such as H2O, surrounding the Shuttle can potentially absorb light from astronomical sources giving false, partially attenuated spectra (visible, i.r.), and can contaminate those types of particle/optical detectors that are open to the vacuum. Particulate matter can settle out on optical surfaces, reducing their transmission, and can scatter unwanted light from the sun or the Earth into the line of sight of a telescope. Vehicle glows may stand in the way of a telescopic line of sight, adding spurious signals and limiting the sensitivity of astronomical or Earth observations. While a great deal of attention has been given to the Shuttle environmental parameters as potential problems for Shuttle users, we wish to stress that so many of the original requirements on the Shuttle have been met that perhaps undue emphasis can now be seen to have been given to these problem areas. This emphasis may have been strong enough to make it hard for users to know, a priori, that the Shuttle is, in fact, a working spaceship ready to convey many successful instruments into space over the years ahead. Two elements currently important for users of the Shuttle are 1) to have a candid and complete description of the environment in the pay load bay on-orbit, controversies notwithstanding, and 2) to make sure that the Shuttle environment is not only consistent with any given set of measuring instruments but also steadily improves with successive launches. In an effort in this direction, Scialdone has recently presented a baseline model for the gaseous and particulate environment of the Shuttle bay. The developing Shuttle bay data base provides both a test bed for such models and a means for extending them. In this paper we concentrate on the data (and interpretation thereof) from various early STS flights, with regard to the gaseous envelope surrounding the Shuttle, the particle populations in orbit with the Shuttle, and the optical interferences from local (rather than astronomical) sources. It seems that many design goals for the on-orbit environment have been met. On the other hand, the environment is very variable, depending upon angle of attack, thruster events, water dumps, solar angle, and payload bay activities. We will attempt to highlight the role of these effects whenever possible.