From your calculator page: <font color="yellow">Delta-v for continuous thrust transfers is the difference in orbital velocities between departure and arrival orbits.</font><br /><br />Um, I don't think so. Gravity losses are continuous and they add up to a large number compared to a transfer which is 100% energy efficient, which is Hohmann and only Hohmann.<br /><br />That paper I linked to a while back spelled it out. LOTS of coupling and gravity losses. The only reason continuous low-thrust works is the high Isp, allowing you to (eventually) deliver the MUCH higher dV needed as compared to near-instantaneous impulse trajectories.<br /><br />Any faster-then-Hohmann trajectory is higher dV than Hohmann, not just because of gravity losses, but primarily because the spaceship and planetary velocity vectors do not match direction. That's what Hohmann is all about: parallel vectors, lowest dV.<br /><br />With non-parallel vectors, some of the energy you expend thrusting is in a direction which does you no good <b>in terms of orbital energy.</b> This is what the concept of 'bound energy' is about. Some of the energy you spend getting to where you need to be (and at the right time to be there) does not get 'bound' to the orbit. Specifically, the radial component of any thrusting only affects potential energy, while tangential thrust contributes all kinetic energy. But only half of the PE is bound to the orbit (see the vis-viva equation). At least that's my understanding after years of beating my head on this stuff. <img src="/images/icons/laugh.gif" /><br /><br />With continuous thrust, you basically NEVER have parallel velocity vectors. Therefore there is no way they can be the loss-free value, which is what you get when you just look at the difference in orbital energies, as you indicate you are doing.<br /><br />Just to be clear, note that when I talk about dV, I'm talking about spaceship capability, not just a mathematical comparison of orbital speeds. Actual astrogation <div class="Discussion_UserSignature"> </div>