Apollo CSM + RM
In 1967 it was planned that Saturn IB-launched Orbital Workshops would be resupplied by Apollo CSM spacecraft and Resource Modules (RM) with up to three tonnes of supplies and instruments. Following launch by a Saturn IB, the Apollo would back away. Then it would transpose and dock with the RM. These RM's could be left docked to the Workshop. Later the Orbital Workshop became Skylab, launched by Saturn V, and the RM's were not needed. A descendent of the RM flew as the Apollo-Soyuz Docking Module.
Credit: McDonnell Douglas Big Gemini Briefing, Dec 1967
AKA: Apollo-I;Resupply Module. Status: Study 1967. Payload: 3,000 kg (6,600 lb). Thrust: 97.86 kN (22,000 lbf). Gross mass: 18,600 kg (41,000 lb). Unfuelled mass: 17,400 kg (38,300 lb). Specific impulse: 314 s.
Following launch by a Saturn IB, the Apollo would back away, transpose, and dock with the RM, just as with the Lunar Module for the lunar missions. These modules could be left docked to the Workshop docking module. Later the Orbital Workshop became Skylab, launched by a Saturn V, and the RM's were not needed. However a descendent of the RM flew in the form of the Apollo-Soyuz Test Project Docking Module.
An even earlier iteration of the concept was in 1963. In 1962 NASA funded studies with several contractors on Operations and Logistics for Space Stations. North American's study was dated 18 March 1963 and proposed two alternatives, the first of which was an 'Apollo-I' derivative of Apollo, with a cargo resupply module.
Crew Size: 3. Orbital Storage: 90 days. Habitable Volume: 6.20 m3. RCS total impulse: 3,530 kgf-sec. Spacecraft delta v: 200 m/s (650 ft/sec). Electric System: 670.00 kWh. Electric System: 6.30 average kW.