## What the heck is Vinf?

21 Mar 2013, 21:35 UTCWhat the heck is Vinf?The internet is a great resource for isolated students like me without access to university libraries or college classrooms. But often Google will land me on a page over my head. I often see strange and unfamiliar terms.Years ago I found myself gnashing my teeth and crying "What the heck is Vinf?!"Then, as now, Vinf was a common term appearing on web pages teaching orbital mechanics.Here is a screen capture from Atomic Rockets, a popular resource for science fiction writers:(red underlines added by me)And here's a screen capture from a Wikipedia article on hyperbolic orbits:(red underlines added by me)In the Wikipedia article they use the symbol for infinity instead of inf. By now you may have guessed Vinf is short for a hyperbola's velocity at infinity.But why would we be interested in something an infinite distance away?A hyperbola gets closer and closer to a straight lines called asymptotes. And as an object moving along a hyperbolic orbit gets farther from the earth, it's speed gets closer and closer to Vinf. A million kilometers out, the actual speed is so close to Vinf that we might as well call it Vinf. From page 36 of my orbital ...