# Max final speed of a Falcon 9 2nd stage after being refueled in LEO?

Starship payload to LEO is about 100 tons

Falcon 9 second stage needs about 100 tons of propellant.

If a Falcon 9 second stage waits in orbit, a Starship comes and refuels it, then Falcon 9 uses all that fuel towards Pluto then how fast the Falcon 9 or its payload can get? Can it get faster than New Horizons 16 km/s ?

More or less of course.

• Nice idea, but it seems this is a bit unbalanced - a second stage with little payload can already reach escape velocity (maybe a bit more, maybe a bit less), so "waiting in orbit" seems like a waste of fuel. With a huge payload, the question about 'max speed' is a bit weird though... – asdfex Nov 26 '20 at 19:26
• Ok then let's assume the payload is New Horizons. Starting with full tanks from orbit is probably faster than starting from sea level – Joe Jobs Nov 26 '20 at 19:33
• Where does your "New Horizons 16 km/s" come from? Is that a delta-v, the square-root of a geocentric C3, or an actual velocity in some coordinate system? Please cite your source – uhoh Nov 27 '20 at 0:32
• Wikipedia On January 19, 2006, New Horizons was launched from Cape Canaveral Air Force Station by an Atlas V rocket directly into an Earth-and-solar escape trajectory with a speed of about 16.26 km/s – Joe Jobs Nov 27 '20 at 0:45
• Second stage has a $\Delta v$ of about 10 km/s with a 500 kg payload, plus about 4 km/s from the first stage. That gives a total $\Delta v$ of 24 km/s. Translating this into an escape velocity taking Oberth into account, I'll leave to somebody else. – asdfex Nov 28 '20 at 11:16