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P. L. Bender (University of Colorado), C. J. Hogan (University of Washington)
The Laser Interferometer Space Antenna (LISA) mission is being planned as a joint ESA-NASA mission to carry out detailed gravitational wave observations at frequencies from a few microHz to a few Hz. Laser heterodyne measurements will be made between 3 spacecraft separated by 5 million km distances in order to determine small changes in the baselines defined by freely floating test masses in the spacecraft. 6 main beat signals are potentially available for analysis. Armstrong et al. recently have pointed out that different combinations of these signals can be analysed, including one called the Sagnac observable that is quite insensitive to gravitational waves below about 30 mHz but gives a valuable measure of the instrumental noise. Tinto et al. have proposed using the Sagnac observable to calibrate the instrumental noise and permit reliable studies of the confusion noise generated by binaries. We will discuss the advantages of using the Sagnac calibration approach plus strong smoothing of the resulting average gravitational wave spectrum for the study of astrophysical and primordial backgrounds. This approach gives essentially the same sensitivity as having two similar antennas to cross-correlate, a method that has been investigated recently by Ungarelli and Vecchio for space missions. Several types of astrophysical backgrounds will be discussed, with the main emphasis on the background due to extragalactic close white dwarf binaries.