A positioning boom disposed between a space-based observatory platform and its instrument payload provides thermal and dynamic isolation as well as fine pointing and momentum control. The inventive system isolates a sensitive payload from a warm, dynamically noisy spacecraft, which includes a sunshield. Isolation is required in terms of dynamics and heat flow, both in terms of the absolute level and its variance (thermal isolation). The present invention provides intrinsic control over momentum buildup (which is due to the separation of the center of pressure from the center of mass). The space-based platform also provides a view (field of regard) to at least half the sky (in the anti-sun direction).