Readers of The Water Cure may recall that the secret Skylark mission’s purpose in the novel was obscured with the fiction that the launch would lift an unmanned, remotely-operated Apollo command/service module spacecraft to dock with the Skylab space station in orbit, providing an escape module for astronauts there in the event that their spacecraft were to malfunction.

There actually were plans for a Skylab Rescue Mission, if needed, using a Saturn 1B booster and an Apollo spacecraft to be flown by two astronauts with extra acceleration seats affixed within its command module.

This Wikipedia article summarizes the history of the effort which, fortunately, was never needed — in spite of some concern over one Apollo craft’s RCS (Reaction Control System) thrusters, vital in turning and orienting the spacecraft.

https://en.wikipedia.org/wiki/Skylab_Rescue