Thanks for the info, never realized the tether would need to be so long!
Now just wondering why they need light propulsion, the platform should be able to just winch up the tether.
The elevator cars do “winch up” the elevator cable... but the power to run the “winch” has to come from somewhere. Eventually there will be a solar power station at the top of the beanstalk that will beam the juice down to the cars, but for now it’ll have to be sent up via a laser beam.
Tether the payload to a counterweight in orbit at the platform. As the payload rises the counterweight and tether are paid out to a higher orbit, then winched down, not up, from the platform.