Actual overall return based on the decision to regularly insert the ET are unknown. There are two numbers that may hint at the overall value. They are presented on the graphs to follow. The first number is the value of scavenged residual cryogenics at a rate of 12 and 24 launches per year for ten years starting in 1986. This number is based on the $2000 per pound launch cost. The second number is the value of raw aluminium at 53,000 pounds per ET at the same two launch rates and cost per pound to orbit. Note that each flight which inserts an ET into LEO is worth $30M in residual cryogenies available for scavenging and $106M in aluminium. Additional returns from the decision to use the ET in space depend on the actual application. Intangibles such as increased commercial interest and business expansion into space due to relativley inexpensive facilities are very difficult to measure. The increased capabilities of a program that extensively uses the ET are also difficult to measure monitarily, but they certainly are extremely valuable in the long run. There is also no way to measure the positive value to the space program that suddenly becomes rich in terms of mass in orbit, structures in orbit, and reaction mass. The two analyses of actual tank applications involving hardware - the ACC and cryogenic scavenging - have not presented any unpleasant suprises. Both applications appear to be not only possible but are potentially very valuable to those interested in affordable space based operations. At this time there appear to be no unknowns. Other than the materials processing facilities and the aluminium engine, there are no applications that require any great investment of R&D funds to accomplish. With few exceptions, every suggested tank application appears to be possible. These proposed applications also appear to be significant improvements in the capabilities of this nation in space. The figure that follows lists hardware R&D, and questions to be answered for the future use of the ET in orbit. Most of the major questions have been answered. Most of the R&D is already being done as part of the space station program. Most of the necessary hardware either already exists or is in development for other space-based operations.
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