The Sling Shot Satellite
You can see how the little red dot is transfered from ground up into the sky.
Here the speed and movement of the different parts is shown with arrows. The system can be constructed
so that the cargo ( red in the first picture ) will catch another sling higher up and with suitable speed.
There can even be up to ten slings pulling the cargo in higher and higher orbits.
And finally the cargo will fly out to the moon or whatever there is in the sky. To keep the power of the
slings in condition, there can be loads taken from the moon and transferred to earth through the system
of slings.

On the moon these slings are easy to put in orbits as the moon has no atmosphere. And they will remain in orbit any amount of time. So going to the moon will need very little energy. The same is the case when
going to the other planets or to some space station. And coming from the moon will really generate energy. In order to trim the paths of every part there are needed some rocket engines. But the better
the system performs, the less these rockets are needed.

The system with relatively short slings is realistic, as the lines don't need to bee horribly long. Instead there will be many slings in different orbits.
The load or satellite unit can be brought up to the first sling with an aircraft.
The cetral unit of a sling must be rather heavy, not to change path too much when
the load is fixed to the hook and later relased upwards.

A regular traffic to the moon is possible once these slings are made to work .
Also there will be very little energy needed to keep this traffic going.

In future there will be slings sending units to other planets on regular basis.
If such a large system is made to work then there can be important materials
brought from other planets with little costs.
Short movie on Youtube