multistage rockets. The OTRAG design used parallel stages assembled from parallel tank tubes with flat bulkheads. The rockets were designed to carry loads up to two tons, the then usual weight of a communications satellite, into a geostationary orbit. It was planned to later increase the capacity to ten tons or more using multiple identical modules. The rocket was to consist of individual pipes, each 27 cm in diameter and six meters long. Four of these pipes would be installed one above the other resulting in a 24 meter long fuel and oxidizer tank with a rocket engine at the lower end making up a CRPU. The fuel was intended to be kerosene with a 50/50 mixture of nitric acid and dinitrogen tetroxide as an oxidiser. Ignition was provided by a small quantity of furfuryl alcohol injected before the fuel, which ignites hypergolically (immediately and energetically) upon contact with the nitric acid. To simplify the design, pumps were not used to move the fuel to the engines, instead the fuel tanks were only 66% filled, with compressed air in the remaining space to press propellants into the ablatively cooled combustion chamber. Thrust control is by partially closing the electromechanical propellant valves. Pitch and yaw control can thus be achieved by differential throttling. In principle this is extremely reliable and cheap in mass production. The modular design was intended to result in a large cost reduction due to economies of scale. The CRPU-based satellite launching rocket was estimated to cost approximately one tenth of conventional designs. Automated production processes for all components would reduce labor cost from 80% to 20% and remove the justification for reusability of spent stages. One large 4 stage configuration OTRAG 10K was supposed to launch a payload of 10,000 kg to a 185 km Orbit. The planned liftoff thrust was around 26 MN with a total mass of 2,300 tonnes: stage 1 : 456 CRPU stage 2 : 114 CRPU stage 3 : 48 CRPU stage 4 : 7 CRPU Controversies and future outlook Only a few political controversies are known concerning OTRAG, which involve the concerns of neighbors in Zaire and Libya about the dual use potential of rockets. A full orbital launch vehicle was never assembled. Modules were flight tested in Zaire and Libya. 6,000 static rocket engine tests and 16 single-stage qualification tests were made to prove the concept as feasible . Hans