IV-A-5. Mass Properties W. Heineman & L. E, Livingston Spacecraft Design Div. a. Weight Growth Weight growth occurs through the various phases of every major program. For all aerospace vehicles, the usual range of weight growth is between 5 and 50 percent, represented by low-risk design aircraft and complex, advanced spacecraft respectively. The value of 50 percent weight growth has been chosen because of the advanced nature of the SPS. Although it is reasonable to assume that advancements will be made in materials and design and fabrication techniques, these advancements will be more than offset by the inexorable weight growth that occurs based on historical data. Figure IV-A-5-1 shows the general pattern of weight growth for various aerospace vehicles from program beginning to end. It should be noted that the data used to develop these curves is from the acquisition phase of the vehicle programs; zero percent growth coincides with the original specification weight or control weight. This is because the weight growth during the definition phase is not sufficiently documented to be shown. In many cases, however, the weight growth during the definition phase has been substantial and had a definite impact on the total weight growth. The Mercury spacecraft as shown in figure IV-A-5-1 grew about 30 percent throughout the acquisition phase. The Gemini spacecraft is generally considered a second-generation vehicle based on Mercury although it still grew about 18 percent. The Apollo Command Module grew over 50 percent primarily because of new technology that had to be developed to go into and return from deep space. It should be pointed out that the above three spacecraft represent essentially all dry weight so that it was not the addition of propellant that caused the weight growths. The Apollo Lunar Module grew over 20 percent in dry weight and over 50 percent in gross weight. However, a substantial portion of the gross weight growth was caused by increases in propellant. Aircraft appear to have the lowest average weight growth of aerospace vehicles. The low average value of 5 percent is primarily due to the low level of advanced technology required as well as established design techniques. This has been a big factor in the design and fabrication of the Space Shuttle Orbiter to date. Although a 10 percent weight growth was chosen for the Space Shuttle Orbiter, it appears that this will be exceeded. The shaded values of figure IV-A-5-1 represent an average of around 40 percent growth. Since the SPS is still in the definition phase, an additional 10 percent for a total of 50 percent weight growth allowance is felt to be realistic at least until the acquisition phase is begun.
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