The name Gravity's Rainbow refers to the parabolic path of a rocket trajectory influenced by the gravitational force of earth.
In World War Two, V2 rockets were launched towards England from stations in locations around Europe. A shining vapor trail was left behind by the rocket in the sky, with one end anchored in Europe and the other at the point of destruction where the rocket exploded. This metaphor is just an example of how Pynchon shows the beauty and elegant mathematical equations of technology which was designed by man for the ugly purpose of terror and destruction.