  Interstellar clouds form the cosmic "ecosystem" through which the Sun moves.
Understanding the physical properties of nearby interstellar material, in
sufficient detail to evaluate historical variations in the solar galactic
environment, requires a survey of ultraviolet interstellar absorption lines
towards stars within 20 pc with the STIS spectrometer. A complete survey would
yield ionization, temperature, density and velocity for nearby interstellar
clouds, and would require a large number of Hubble Space Telescope orbits
spaced over several cycles. This note was submitted as a "white paper" to the
Space Telescope Science Institute in support of multi-cycle treasury programs.
