100 Years of Relativity Space-Time Structure: Einstein and Beyond ...

Receiving Gravitational Waves 243In almost the same sense as the early table-top interferometers were prototypesof larger instruments, so too did the proposals for kilometer-scaleinterferometers have a prototype. This was the report called “A Study of aLong Baseline Gravitational Wave Antenna System”, submitted to the U.S.National Science Foundation in October 1983. 21 (It has since its presentationbeen called the “Blue Book” because of the color of the cheap papercover in which it was bound.) It was prepared as the product of a planningexercise funded by the National Science Foundation starting in 1981. Themost novel feature is that, in addition to sections describing the physicsof gravitational wave detection, it also contains extensive sections writtenby industrial consultants from Stone & Webster Engineering Corporationand from Arthur D. Little, Inc. These latter contributors were essential,because this document contains, for the first time anywhere, an extensivediscussion of the engineering details specific to the problems of the constructionand siting of a large interferometer. The report was presented bythe MIT and Caltech groups at a meeting of the NSF’s Advisory Councilfor Physics late in 1983. While not a formal proposal, it served as a sort of“white paper”, suggesting the directions that subsequent proposals might(and in large measure did) take.The industrial study was undertaken with the aim of identifying whatdesign trade-offs would allow for a large system to be built at minimum cost,and to establish a rough estimate of that cost (along with cost scaling laws)so that the NSF could consider whether it might be feasible to proceed witha full-scale project. Before such an engineering exercise could be meaningful,though, it was necessary to define what was meant by “full-scale”. The BlueBook approaches this question by first modeling the total noise budget as afunction of frequency, then evaluating the model as a function of arm lengthsranging from 50 meters (not much longer than the Caltech prototype) to50 km. The design space embodied in this model was then explored in aprocess guided by three principles:• “The antenna should not be so small that the fundamental limitsof performance can not be attained with realistic estimates of technicalcapability.” This was taken to mean that the length oughtto be long enough that one could achieve shot noise limited performancefor laser power of 100 W, without being limited insteadby displacement noise sources, over a band of interesting frequencies.The length resulting from this criterion strongly depended onwhether one took that band to begin around 1 kHz (in which case