Star visibility and tracking from the Space Station

Abstract

Purpose of the present study is to provide algorithms for and examples of how to simulate star visibility and tracking by a Telescope attached to the main truss of the International Space Station (ISS). The sky visibility of a Telescope is limited by accommodation constraints on the truss, by obstructions caused by Station’s structural elements along with other payloads, by Sun and Moon’s light and by ram atomic Oxygen. It is also limited by Station’s orbit and attitude. The above limiting agents have been modeled vis-a-vis NASA nominal specifications and knowledge of the ambient environment. These models have been used to write algorithms and to produce examples of visibility and tracking at single star level. The above analysis has been used to describe in detail how to simulate star visibility and tracking of an observing program all over the sky by a plausible wide field Telescope operated only during successive 80 days coast periods in the declination’s range −71° to 71°. Simulation is mandatory in advance of real observations. The analysis rests on the feasibility study, funded by the Italian Space Agency (ASI), of a Telescope designed for accommodation on ISS. The present visibility and tracking study enables observations planning and it is introductory to any engineering algorithm devoted to mechanically drive pointing and tracking of celestial targets from the Space Station. Since question might arise whether ISS-based Astronomy is nowadays scientifically worthwhile, a brief summary of the science rationale in Ultraviolet, useful to Astrophysics and Cosmology, is offered to the curious Astrophysicist who can decide on his own. From an operational point of view it is concluded that an observing programme can be carried out provided photon re-centering techniques are applied to the raw data, in order to free them from the effects of ISS vibrations.