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The study identified exactly how many launches of the Shuttle and a Shuttle-derived heavy lift vehicle would be required , and concluded that the project could have begun in 1985 and have three SPS 's on line by 1992 . Later this morning , the astronauts plan to conduct the first of several rendezvous burns of the Shuttle 's maneuvering jets to begin to close in on Hubble , which is scheduled to be retrieved by Discovery 's robot arm early Thursday morning . Determine the facts , as well as the actual or probable causes of the Shuttle mishap in terms of dominant and contributing root causes and significant observations and , recommend preventive and other appropriate actions to preclude recurrence of a similar mishap .