Jack of Harts

The first orbital elevators were built as a single tether from Earth to orbit. You could send packages up or down, but not both at the same time. One had to be careful with the schedules. The obvious first upgrade was to add a second tether, one for lifting and one for dropping. The Panama City Elevator was the first purpose built dual-tether elevator. Yes, they actually considered two tethers to be sufficient back then. The modern Panama Station and her tethers would amaze them.