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starship-design: Am I missing something?

Curtis L. Manges writes:
 > The following quote was taken from the article, >>"Richter Scale" of
 > Asteroid Impact Threats Announced<<  released on Spaceviews, here:
 > http://www.spaceviews.com/1999/08/
 > "Some asteroids, such as 1999 AN10, at one time measured a 1 on the
 > [Torino] scale, meaning that they had about an equal probability of
 > striking Earth as a random, undiscovered object of similar size."
 > Now, I've got to wonder: if an object is "undiscovered," how we can know
 > anything about its size, or its probability of striking Earth? I feel
 > it's important to clarify this, because it would seem to suggest that
 > our asteroid experts are postulating  the likelihoods of specific
 > events, with NO real-world information to base their judgments on. This
 > can't be true, can it?
 > If any of you folks know anything about how these people do their work,
 > I'd enjoy a little bit of enlightenment about it, as I'm sure a lot of
 > us would.

You can obtain the approximate historical probability of the
Earth being struck by asteroids based on geological evidence of
previous impacts.  So it may not be as silly as it sounds to talk
about the probability of the Earth being struck by undiscovered
objects, although it would be nice to know more about how they
came up with the numbers.