SpaceX to supply lunar missions with new Dragon capsule – IT Pro – News

An addition:
The elliptical orbit means that you can indeed reach the Lunar Gateway with less energy. But from the Lunar Gateway it is more difficult to go to the surface of the moon with a soft landing. (very hard crash is cheaper in terms of energy).
It is therefore about how many Earth LunarGateway transports you want to make and how many LunarGateway Moon transports you want to make. That ratio determines the most efficient elliptical orbit.

To clear up a misunderstanding for readers: to do a rendezvous in space, you must be in the same place and move at the same speed (svector). Both objects are therefore in the same orbit at the time of the rendezvous.

So it is not the case that during a trip to the moon you can stay nice and far from the moon to do a rendezvous with the LunarGateway and then let any cargo fly further with the LunarGateway closer to the moon. There is no free energy there.

The gain is therefore purely that a orbit around the moon with a farthest point of the moon (apoapsis) that is high costs less energy than a orbit where that apoapsis is closer to the moon.

More simply explained: to descend to the moon orbit, the vehicle must brake. With a track that largely still has the orbit far from the moon, a rendezvous requires less braking. Saves energy to achieve and then less speed has to be regained back to earth.

[Reactie gewijzigd door Tjeerd84 op 29 maart 2020 14:21]

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