Pwokenyaw said:

"My impression so far is that a delay of 100 years in colonizing space would make virtually no difference in avoiding random human extinction events, because they happen so rarely."

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If technology was never forgotten and manufacturing capability never lost then the above argument would be valid. It is a relatively recent phenomena for human beings to use the scientific method for developing new technology to improve their lives. The ancient Romans inherited Hellenistic Greek science and mathematics but did almost nothing with it. Copernicus developed his helocentric theories from ancient astronomical observations made in Hellenistic times. Archimedes had access to the same information that Copernicus used. Archimedes was a brighter guy than Copernicus but simply wasn't interested in astronomy. Nobody after Archimedes had the mental horsepower to develop the heliocentric model until Copernicus came along over 1700 years later.

Human interest in science and technology passes in-and-out of fashion. American aerospace technology is currently going the way of 19th century mining technology and early 20th century naval architecture. Much of aerospace technology cost hundreds of billions of dollars to develop, e.g. ballisitic missiles and reentry vehicles. This technology would probably never have been developed had it not been for the Cold War. A lot of basic aerospace technology has already been forgotten. Case in point: Most American entry vehicles have a base radius to nose radius ratio of 2:1, e.g. Viking, Mars Pathfinder, MER, Pioneer Venus, Mk-6, etc. There was a good reason for this ratio but no one remembers what it was. We keep reusing that ratio due to design legacy (it seems like a good idea and no one can come up with a reason not to continue).

IHMO, the American Space Program is currently poised to implode. If Bush's Vision for Space Exploration morphs into a simple lunar Flag-and-Footprints exercise then the American civilian Space Program maybe dead beyond ressurrection by 2050. If a killer long period comet is discovered in 2080 then no humans will escape the Earth before impact because the necessary technology will have been forgotten. We should have immediately begun a Mars colonization program the moment we had the basic technology (that was after 1970). As we threw away the Saturn-V, NERVA and Space nuclear reactor technologies, the problem of colonizing Mars just got harder-and-harder.

Our species is probably not fit to survive but I'd like to be proven wrong about that.

Gary