Otrag rockets would have been assembled from clusters of Common Rocket Propulsion Units (originally called modules, but von Braun pointed out that the M could be construed as "Missile", further fuelling the charges of OTRAG's critics). These CRPU's properties and dimensions were optimized to achieve one and one only goal: Minimum transport cost per unit of payload mass to low earth orbit and beyond. The $ 200 million spiral development and test program took 40 years, went through more than 1000 versions, included over 6000 static tests firings with total burning time approaching one million seconds, and achieved 14 suborbital test flights. The CRPU was human-rated and had a confidence level higher than 6-sigma. Main characteristics were:

• Thrust: 25,000 N (5,000 lbf)
• Oxidizer: High Density Acid (HDA) (50% N2O4- 50% HNO3) Den: 1.66 gr/cm^3
• Fuel: Diesel fuel or Kerosene
• Specific Impulse: First stage - 270 seconds, Stages 2 and 3 - 297 seconds vacuum
• Injection pressure: 40 - 15 bar
• Thrust control: 100% - 40 %
• Pressurization: Compressed air, 66% tank filling in blow-down mode
• Injector: Radial like on like
• Chamber cooling: Ablative phenolic
• Mass total: 1,500 kg
• Mass empty: 150 kg
• Material of injector, valves, bulkheads: AlMg5
• Material of cylindrical tank sections: cold-rolled low-carbon stainless steel
• Dimensions: Diameter 0.27 m, Length: 16 m
  A small launch vehicle with a 1 metric ton payload to low earth orbit would have consisted of 4 CRPU's in the third stage, 12 CRPU's in the second stage, and 48 CRPU's in the first stage. These were stacked in parallel in a quadratic ring arrangement. Larger vehicles would be assembled using hundreds or thousands of identical CRPU's. //

Orbital Transport-und-Raketen Aktiengesellschaft, Germany. Manufacturer of rocket engines and rockets. $200 million was spent from 1975-1987 by Lutz Kayser in a serious attempt to develop a low-cost satellite launcher using clusters of mass-produced pressure-fed liquid propellant modules. The project was finally squelched by the German government under pressure from the Soviet and French.

• Status: Retired 1983.
• First Launch: 1977-05-18.
• Last Launch: 1983-09-19.
• Number: 18 .
• Payload: 1,000 kg (2,200 lb).
• Thrust: 1,170.00 kN (263,020 lbf).
• Gross mass: 100,000 kg (220,000 lb).
• Height: 24.00 m (78.00 ft).
• Diameter: 0.76 m (2.49 ft).
• Apogee: 185 km (114 mi).