The Drake Equation is drivel masquerading a science.
How many of the terms in the equation are knowable within three orders-of-magnitude?
They don’t have to be known for the equation to be valid. Knowable or unknowable is a different question, of course, but I’m not sure any of them are truly unknowable in the sense that they couldn’t be estimated. We have to remember we’re just trying to estimate N.
Secondly, Crichton seems to be under the impression that the Drake equation has to be “testable.” Nothing could be further from the truth. The equation involves a simple application of the “multiplication rule” for probabilities that every freshman statistics student must learn. Then the student can use that rule innumerable times to do various homework problems. He doesn’t have to “test” it each time to see if it’s true.