The Ark in Space is a work of political philosophy, set in the context of man's exploitation of planet Earth to fulfil his various needs. The work offers a hypothesis - that planet Earth has a finite capacity to sustain man's manipulation of his environment as he pursues his inexorable drive to enrich himself. On the basis of this hypothesis the work suggests that the political consequences of planet Earth only having a finite productive capacity relative to what man may desire in terms of its output has implications that entail revisiting and reappraising the ideals of liberty, equality and fraternity. The hypothesis in order to resonate employs a metaphor designed to encapsulate the suggested finite ability of planet Earth to accommodate the ever increasing demands that man places upon it to facilitate the 'good life'. The metaphor envisages Earth as an Ark in Space. It is designed to condense our thinking about the ability of the planet to sustain man's manipulation of it to suit his consumptive needs. Planet Earth, the Ark in Space is the common good which must be sustained through combined and concerted fraternal action, driven by a philosophy of conservation as opposed to consumption.