In the late 1960’s H.H. Koelle of the Technische University Institut Fuer Raumfahrttechnik in Berlin devoted considerable effort to studying a reusable heavy lift launch vehicle. A good, well-illustrated report was put out in 1968 covering the design:
Entwurfskriterien fur groBe wiederverwendbare Tragersysteme (Design Criteria for Large Reusable Space Transportation Systems)
Note that the Neptun was *gigantic.* It was a two-stage ballistically recovered design, unusual in that rather than being circular in cross-section it was hexagonal. The individual propellant tanks were each the size of or bigger than the S-IC first stage of the Saturn V.
A number of payloads were proposed. One was a sub-orbital intercontinental passenger transport, The passenger “capsule” would land separate from the Neptun itself.
One of the more interesting payloads contemplated was a large Orion nuclear pulse vehicle, transported in two pieces (propulsion module in one launch and payload/pulse units in the other). Presumably this would be a NASA Orion hitching a ride on a West German booster; I suspect politics would have negated the likelihood of the West Germans developing a mass production line for nuclear explosives.
This fusion-powered interplanetary spacecraft is also a NASA design, dating from the early 1960’s.
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