the crew of the Andrea Luhman stranded on Earth in the middle ages faced a seemingly impossible challenge. They, and their Viking allies, could save humanity from extinction in a war in the distant future only by building a space program capable of launching a craft into Earth orbit starting with an infrastructure based upon wooden ships and edged weapons. Further, given what these accidental time travelers, the first in history, had learned about the nature of travel to the past in their adventures to date, all of this must be done in the deepest secrecy and without altering the history to be written in the future. Recorded history, they discovered, cannot be changed, and hence any attempt to do something which would leave evidence of a medieval space program or intervention of advanced technology in the affairs of the time, would be doomed to failure. These constraints placed almost impossible demands upon what was already a formidable challenge.