The author's fictional works (Mars trilogy for instance) speculate that it would require the concentrated effort of the human race (via a UN type government or corporation) and Von Neumann factory robots that can replicate themselves or other robots and hundreds of years of a multiple pronged approach in space around Mars and on surface of Mars - spread out over many thousands of acres, just based on what we knew at the time of the writing. At the present time we cannnot make a Von Neumann automata outside of paper or electronic versions.