In response to a question below, here is what’s inside the orbital Ascender. Specifically it’s not a single balloon but a array of lifting cells.
This drawing is from the book “Floating to Space, The Airship to Orbit Program”. If you don’t have a copy get yourself to the front page of the JPA site, click on the picture of the book in the upper left corner and buy one!

Thanks. This whole concept is elegant.