Gravitation is a force human kind encounters everywhere, one which remained unconquered for the vast part of human existence.
When physicists look at gravitational fields, they consider all objects within a given field to have negative energy to indicate their captivity in that gravitational field. If an object has exactly enough energy to escape that field, it has 0 energy. In essence when it goes beyond that 0, it becomes free from the gravitational system. This bit describing the rocket's ascent at the very end made me think of a possible explanation for what constitutes going "beyond the zero":

As I was reading the last lingering pages, I came across this passage. Yes, I must admit, I did find another ROCKET parallel!
On page 760 it reads, "The title is New Dope, and that's what it is about, a brand new kind of dope that nobody's ever heard of. One of the most annoying characteristics of the shit is that the minute you take it you are rendered incapable of ever telling anybody what it's like or worse, where to get any. Dealers are as in the dark as anybody. " I thought this passage was so interesting because it was just another rocket metaphor and, I think, a strong theme for this book.