ET Project - Introduction I. Introduction This report was written under a grant from the Space Studies Institute of Princeton, N.J. The scope of the project is to research all the proposed on-orbit applications of the External Tank (ET) and write a report detailing the results of the research. The report is intended first for presentation to the National Commission on Space and second to provide an overview of current and past External Tank applications studies. The list of references in the back of the report, with the listing of those contacted during the research, will hopefully provide a source of additional information to those interested in the ET and its applications in space. I wish to thank all those listed on the pages following for their time, help, patience, and comments in completing this work. II. Why do we need the External Tank? The ET is the only portion of the Space Transportation System (STS) currently expended on each flight. A typical launch will retain the ET for the SSME burn of over eight minutes and then jettison it for a controlled reentry in either the Indian or Pacific Ocean. An alternate launch trajectory called a direct injection can allow a shuttle to take an ET, an average of 15,000 pounds of residual cryogenics (16), and up to 2,000 pounds additional payload into a typical space station orbit (68). In other words, it costs nothing to deliver a 69,000 pound, factory tested, aluminium pressure vessel into low earth orbit (LEO). In an era of launch costs running about $2,000 per pound to LEO(69), this is clearly a resource worth utilizing in future space based operations. Each and every shuttle launch can deliver a tank to orbit. This can amount to several hundred tanks over a ten year period. The economic analysis of tank utilization on-orbit typically compares costs between a ground built and launched structure and a similar structure built on orbit out of the ET or parts supplied by the ET. These studies alone make ET applications on-orbit extremely attractive. There are additional benefits that the ET can provide in orbit which can not be provided by a ground based item. These make the ET a better choice for almost every manned space operation currently envisioned. Why do we need the ET? We need it because it
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