Fifteen years of observing from low Earth orbit

Hubble Space Telescope has been operating from low Earth orbit for 15 years. In the case of HST, the orbit was determined by launch and servicing considerations, not observing efficiency. Higher orbits have been chosen for recent missions, for various reasons. This paper will discuss the evolution of HST operations in low Earth orbit, comparing the results with early expectations, identifying the changes and improvements made, and identifying the most serious constraints to observing efficiency found in practice. We will generalize this experience to possible future use of low Earth orbit as an observing site, identifying mission design parameters that could improve efficiency, or otherwise make low Earth orbit more attractive as an observing site.