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No, he's right A bi-elliptic transfer is used for transferring between two orbits around the same body. In some situations, this is more efficient than a straightforward Hohmann transfer, at the cost of taking much, much longer. For a Hohmann transfer, you reduce the ship's orbital velocity relative to the sun, reducing the orbit's perihelion to somewhere inside the sun. That requires cancelling out almost all of the Earth's orbital velocity. For a bi-elliptic transfer, you first increase the ship's orbital velocity relative to the sun, increasing the orbit's aphelion to somewhere in the outer solar system. That's your first Hohmann transfer, going apparently the wrong direction, but requires less than 40% as much energy as dropping it into the sun did. Then, at aphelion, when the ship's orbital velocity is lowest, you reduce the ship's orbital velocity to drop it's perihelion inside the sun. From that far out, and at such an eccentric orbit, that requires only a fraction of the energy it did from Earth's orbit. The entire manuever, potentially, could be far more efficient than a direct transfer. It just takes far longer, and if the ship fails to make the second maneuver, it'll be left in an orbit that crosses Earth's orbit. |