Space Telescope orbital viewing constraints

Astronomical observations with the Space Telescope will be constrained by spacecraft operational requirements and capabilities, orbital viewing conditions, and the space environment. While ultraviolet or bright visual-range observations may be performed for 53 to 94.6 minutes per orbit (from a 500 kilometer altitude), certain stray light sensitive experiments may be limited to 0-48 minutes of viewing per orbit. Careful operations planning may make possible observations of 'secondary' targets while a primary target is occulted, of objects as close as 18 deg to the sun, or of objects visible when the spacecraft is in a high radiation environment.