hard limit on the engine diameter, preventing use of an efficient, high-expansion nozzle for the upper stages. However, ganging CRPUs into three stages was sufficient to reach orbit. Meanwhile, the low cost of each CRPU, after the economies of scale gained by producing hundreds or possibly thousands of them per year, would have still left the vehicle cheaper than its contemporaries. The company's baseline launcher design claimed to lift one metric ton to orbit. It would have consisted of a third stage core of four CRPUs, surrounded by a second stage of twelve CRPUs, in turn surrounded by the first stage's 48 CRPUs. Larger vehicles and capacities would be achieved with greater numbers of CRPUs, possibly including several hundred per flight for a heavy launcher. The company forecast that CRPUs would eventually be so cheap, recovering and refurbishing a launcher would be no better than simply building more units. The use of storable propellants and few moving parts meant that launch-site operations would also be very simple. These advantages were expected to overcome the disadvantages of small specific impulse and payload fraction. Flight history The engines were tested extensively on ground rigs, on both German and African test sites. Experiments were run with varying fuel and oxidiser formulations, as the general design was quite robust. Small, 4-unit vehicles were built and tested in Shaba North, Zaire and Seba Oasis, Libya, where heights of 20 to 50 kilometres were reached. The rockets used there were 6 and 12 meters long. The basic CRPU concept was shown to be workable, though some rockets experienced guidance or component failures. The last launch of an OTRAG rocket took place on September 19, 1983 at Esrange. Following this launch, the OTRAG rocket was to be used in high altitude research. Political pressure then shut down the project, as discussed in the OTRAG article. After the company had left Libya in 1987, some remaining equipment was confiscated by the government. However, enough parts and knowledge were missing to prevent Libya from continuing the project. Resurgence of interest John Carmack, CEO of Armadillo Aerospace met with Lutz Kayser, the founding engineer of OTRAG, in May, 2006 who loaned Carmack some of their original research hardware. "I have been corresponding with Lutz for a few months now, and I have learned quite a few things. I seriously considered an OTRAG style massive-cluster-of-cheap-modules orbital design back when we had