this is old school history but it does have some very good ideas! (might kerbal test it)
(don't be fooled, it really would work!)
(one of the Otrag Modules at Site)
"So the idea was to develop a very simple CRPU "Common Rocket Propulsion Unit" which could be bundled in different quantities to produce any sized booster you want. The CRPU would be so simple as to be built out of ordinary steel, pressure feed so no expensive turbopumps, ablatively cooled engine rather than the more elaborate regeneratively cooling, no gimbling (steering the whole rocket will be done via varying the thrust of CRPUs on different sides of the booster) and flat bulkheads rather than the complex domed bulkheads of bigger rockets. Since each individual CRPU is simple and a single complete rocket will require a large number of them, the CRPU factors will be expected to mass produce a huge number of CRPU per year. Mass production of simple machines on this scale has been proven to drive down cost and increase reliability (eg, Merlin engine production during WW2) so OTRAG rockets are projected to reduce launch vehicle cost BY A FACTOR OF TEN!!! compared to conventional rockets. The unit cost of CRPUs will be so cheap that recovering them for reuse will be pointless as the cost of recovery and refurbishment will be greater than just building a new CRPU."
"The idea was so revolutionary that OTRAG (which was a German company) managed to get Wernher von Braun interested and he became their scientific adviser. Von Braun however came to the company with a warning that rocketry is inherently a political process and he did not believe Germany provided a stable enough political environment for rocket development."
"Technical wise the project proved to be quite workable and OTRAG managed 14 suborbital launches with a four CRPU sounding rocket design. But the politics got in the way. The USSR and France were not interested in Germany achieving an indigenous long-range rocket activity. American rocket makers were not interested in having a low-cost competitor. A propaganda campaign began, alleging OTRAG was a cover for German and South African nuclear cruise missile development. Crude Soviet-source disinformation was eagerly picked up and given credibility by the American mainstream media. The government of the Congo (were OTRAG's testing facility was located) was pressured by the Russians to withdraw permission to use the site. OTRAG left the country in April 1979. OTRAG moved their testing to Libya but in 1983 the Libyan Government unlawfully confiscated all of OTRAG's rocket manufacturing and test equipment in the country for their own end and never returned them despite personal promises by Gaddafi. The company gave up and shutdown after those two set backs. "