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The ground system operates through a sophisticated and well-coordinated relay scheme. Scientific data are transmitted from the Space Telescope to a NASA communications satellite, then to a receiving station at White Sands. Transmissions continue via a commercial communications satellite, which sends signals to NASA's Goddard Space Flight Center in Greenbelt, then through land lines to Space Telescope Science Institute in Baltimore. IMSL Libraries routines have been valuable in the construction and daily operation of the science ground system at these sites. The Space Telescope Science Institute The Space Telescope Science Institute (STScI) is operated for NASA by the Association of Universities for Research in Astronomy, Inc. The STScI is responsible for science planning and scheduling and for science data processing and archiving. As the primary center for the science community's interactions with the Space Telescope, the Institute is not only an operational center, but also a well-recognized research facility. Professional and amateur astronomers from around the world request observing time on one or more of the Space Telescope's instruments by submitting proposals to STScI. Once their observation time is scheduled, astronomers are provided with a viewing console at STScI if they wish to be present when their programmed observations occur. The Hubble Space Telescope executes most observations automatically. Step-by-step instructions to the telescope are generated from the science schedule at NASA-Goddard. New instructions are sent up to the spacecraft several times a day via one of NASA's tracking and data-relay satellites. The astronomers and programmers at the STScI have spent years developing special software programs to analyze Hubble observations. The computer programs are written to plan, execute and analyze the Space Telescope's astronomical observations. These programs are composed of approximately two million lines of code. IMSL's Key Role As Operations Software Branch Project Engineer for the STScI, Joseph A. Polizzi, III is one of those responsible for the technical evolution of the science ground systems that support the Hubble Space Telescope. "The IMSL Libraries serve in three critical areas of the ground system: the Observation Support System, the Guide Star Catalog Construction System and the Guide Star Request System," said Polizzi. Through the Observation Support System, operations astronomers and staff monitor and "real time" activities of the Space Telescope and may review the engineering parameters of Hubble's various science instruments during an observation. "The astronomers also get a preliminary (uncorrected) version of the science data taken by the experiment. When preplanned in the mission schedule, they may command minor maneuvers and make other adjustments to properly point the Space Telescope to a given target," said Polizzi. IMSL routines have also been included in the Guide Star Catalog Construction System to construct the Guide Star database. More than 1,400 astrometric plates, taken at various earth-based observatories, are scanned on a high-resolution digital densitometer, and the data are reduced to identify objects from the background noise. Each object is then classified as being stellar, galaxy or unknown, and the centered position and estimated magnitude are recorded into the database. "Accurate selection of a valid Guide Star pair is critical for the precise positioning of Hubble to properly acquire the intended target," Polizzi said. "IMSL routines are used in the Guide Star Request System to select Guide Star pairs from the Guide Star database in response to pointing requests. Typical requests identify targets for some specific apertures of the Space Telescope and with some given time or positional constraints. The Guide Star Request System also provides the planning system with alerts for bright objects that may appear in the field of view for a given pointing," said Polizzi. A Resource for Astronomers Worldwide As a project of international cooperation between NASA and the European Space Agency, the revelations from Hubble's first year in orbit have already confirmed its unique and valuable place as the premier international instrument for the study of the cosmos. Eventually, observers around the world will be networked to the Institute, enabling them to have keyboard access to the data archives there. In the future, as new instruments for the Space Telescope are launched, the science ground system will continue to provide the critical support needed for the observation of space.
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